Document And Entity Information	12 Months Ended
Document And Entity Information	Dec. 31, 2017 shares
Document And Entity Information [Abstract]
Entity Registrant Name	Arcturus Therapeutics Ltd.
Entity Central Index Key	0001566049
Current Fiscal Year End Date	--12-31
Entity Filer Category	Non-accelerated Filer
Trading Symbol	ARCT
Entity Common Stock, Shares Outstanding	10,699,271
Document Type	20-F
Amendment Flag	false
Document Period End Date	Dec. 31, 2017
Document Fiscal Period Focus	FY
Document Fiscal Year Focus	2017
Entity Well-known Seasoned Issuer	No
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes

CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Current assets:
Cash and cash equivalents	$ 24,965	$ 8,345
Restricted cash	166
Short-term investments	23,608
Accounts receivable	480	3,633
Prepaid expenses and other current assets	1,059	353
Intangible asset held for sale	590
Total current assets	50,868	12,331
Property and equipment, net	1,049	1,335
Other assets	107	70
Total assets	52,024	13,736
Current liabilities:
Accounts payable	1,790	3,357
Accrued liabilities	2,793	1,061
Deferred revenue	6,457	4,183
Convertible promissory notes and accrued interest		133
Total current liabilities	11,040	8,734
Deferred revenue, net of current portion	7,190	3,410
Other liabilities		15
Total liabilities	18,230	12,159
Commitments and contingencies (Note 13)
Shareholders’ equity:
Ordinary shares: NIS 0.07 par value; 30,000 shares authorized, 10,699 issued, 10,656 outstanding and 43 held in treasury at December 31, 2017; $0.0001 par value, 2,801 issued and outstanding at December 31, 2016	212
Additional paid-in capital	56,674	13,764
Accumulated other comprehensive loss	(3)
Accumulated deficit	(23,089)	(12,187)
Total shareholders’ equity	33,794	1,577
Total liabilities and shareholders’ equity	52,024	13,736
Series Seed Preferred Stock [Member]
Shareholders’ equity:
Preferred stock value	0	0
Series A Preferred Stock
Shareholders’ equity:
Preferred stock value	$ 0	$ 0

CONSOLIDATED BALANCE SHEETS (Parenthetical)	Dec. 31, 2017 $ / shares shares	Dec. 31, 2017 ₪ / shares shares	Dec. 31, 2016 $ / shares shares
Common stock, par value \| (per share)		₪ 0.07	$ 0.0001
Common stock, shares authorized	30,000,000	30,000,000
Treasury shares	43,000	43,000	0
Common stock, shares issued	10,699,000	10,699,000	2,801,000
Common stock, shares outstanding	10,656,000	10,656,000	2,801,000
Series Seed Preferred Stock [Member]
Preferred stock, par value \| $ / shares	$ 0.0001		$ 0.0001
Preferred stock, shares authorized	0	0	1,284,000
Preferred stock, shares issued	0	0	1,284,000
Preferred stock, shares outstanding	0	0	1,284,000
Series A Preferred Stock
Preferred stock, par value \| $ / shares	$ 0.0001		$ 0.0001
Preferred stock, shares authorized	0	0	2,564,000
Preferred stock, shares issued	0	0	1,481,000
Preferred stock, shares outstanding	0	0	1,481,000

CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE LOSS - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Statement Of Income And Comprehensive Income [Abstract]
Revenue in conjunction with strategic alliances and collaborations	$ 12,998	$ 20,382	$ 6,138
Operating expenses:
Research and development, net	15,918	17,934	5,476
General and administrative	7,572	3,448	2,574
Total operating expenses	23,490	21,382	8,050
Net loss from operations	(10,492)	(1,000)	(1,912)
Finance (expense) income, net	(409)	(536)	11
Net loss before taxes	(10,901)	(1,536)	(1,901)
Income tax expense	(1)	(35)	(1)
Net loss	$ (10,902)	$ (1,571)	$ (1,902)
Net loss per share, basic and diluted	$ (3.53)	$ (0.77)	$ (0.94)
Weighted-average shares outstanding, basic and diluted	3,087	2,032	2,016
Comprehensive loss:
Net loss	$ (10,902)	$ (1,571)	$ (1,902)
Unrealized loss on short-term investments	(3)
Comprehensive loss	$ (10,905)	$ (1,571)	$ (1,902)

STATEMENTS OF CHANGES IN SHAREHOLDERS' EQUITY (DEFICIT) - USD ($) $ in Thousands	Total	Series Seed Preferred Stock [Member]	Series A Preferred Stock	Ordinary Shares [Member]	Additional Paid-In Capital [Member]	Accumulated Other Comprehensive Loss [Member]	Accumulated Deficit [Member]
Balance at Dec. 31, 2014	$ (1,845)				$ 6,869		$ (8,714)
Balance (in shares) at Dec. 31, 2014		1,284	960	2,784
Net loss	(1,902)						(1,902)
Shares issued in conjunction with share option exercise	17				17
Shares issued in conjunction with share option exercise (in shares)				17
Share-based compensation	99				99
Balance at Dec. 31, 2015	(3,631)				6,985		(10,616)
Balance (in shares) at Dec. 31, 2015		1,284	960	2,801
Net loss	(1,571)						(1,571)
Share-based compensation	300				300
Issuance of preferred shares upon convertible promissory note maturity including debt conversion expense	6,479				6,479
Issuance of preferred shares upon convertible promissory note maturity including debt conversion (in shares)			521
Balance at Dec. 31, 2016	1,577				13,764		(12,187)
Balance (in shares) at Dec. 31, 2016		1,284	1,481	2,801
Net loss	(10,902)						(10,902)
Unrealized loss on short-term investments	(3)					$ (3)
Shares issued in conjunction with share option exercise	$ 675				675
Shares issued in conjunction with share option exercise (in shares)	378,343			348
Share-based compensation	$ 2,170				2,170
Issuance of shares upon exercise of warrants	160				160
Issuance of shares upon exercise of warrants				189
Issuance of shares upon conversion of notes	5,957				5,957
Issuance of shares upon conversion of notes (in shares)				617
Conversion of Preferred Shares to Ordinary Shares (in shares)		(1,284)	(1,481)	2,765
Beneficial conversion expense from notes	348				348
Issuance of shares in connection with merger, net	33,812			$ 212	33,600
Issuance of shares in connection with merger, net of refund for fractional shares (in shares)				3,979
Balance at Dec. 31, 2017	$ 33,794			$ 212	$ 56,674	$ (3)	$ (23,089)
Balance (in shares) at Dec. 31, 2017				10,699

CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
OPERATING ACTIVITIES:
Net loss	$ (10,902)	$ (1,571)	$ (1,902)
Adjustments to reconcile net loss to net cash (used in) provided by operating activities:
Depreciation and amortization	410	294	192
Share-based compensation expense	2,170	300	99
Gain on sale of equipment			(11)
Interest expense on convertible promissory notes	150	295	251
Beneficial conversion expense from notes	348	250
Changes in operating assets and liabilities
Accounts receivable	3,153	(1,556)	(2,077)
Prepaid expenses and other assets	(202)	(314)	23
Accounts payable	(1,537)	2,536	240
Accrued liabilities	(104)	303	484
Deferred revenue	6,054	(3,398)	10,991
Net cash (used in) provided by operating activities	(460)	(2,861)	8,290
INVESTING ACTIVITIES:
Proceeds from maturities of short-term investments	10,577
Acquisition of property and equipment	(251)	(688)	(247)
Proceeds from sale of equipment	29		27
Net cash provided by (used in) investing activities	10,355	(688)	(220)
FINANCING ACTIVITIES:
Proceeds from issuance of convertible promissory notes	5,650		1,885
Proceeds from exercise of share options	711		17
Proceeds from exercise of warrants	160
Net cash received in the issuance of shares for the net assets of Alcobra Ltd.	477
Net cash provided by financing activities	6,998		1,902
NET INCREASE (DECREASE) IN CASH, CASH EQUIVALENTS AND RESTRICTED CASH	16,893	(3,549)	9,972
Cash, cash equivalents and restricted cash at beginning of year	8,345	11,894	1,922
Cash, cash equivalents and restricted cash at end of year	25,238	8,345	11,894
Supplemental cash flow information
Cash paid for taxes	35	12	1
Purchase of property and equipment included in accounts payable and accrued liabilities		127	$ 53
Issuance of Series A preferred shares upon note maturity		6,229
Convertible notes and accrued interest reclassified to accounts payable at maturity		$ 151
Fair value of assets acquired, excluding cash, cash equivalents and restricted cash	35,241
Less liabilities assumed	(1,906)
Net assets acquired, excluding cash, cash equivalents and restricted cash	33,335
Conversion of notes to Ordinary Shares	$ 5,957

Organization	12 Months Ended
Organization	Dec. 31, 2017
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Organization	NOTE 1. Organization Description of Business Arcturus Therapeutics Ltd. and subsidiaries (referred to as the “Company”) is a nucleic acid medicines company with enabling technologies – UNA Oligomer chemistry and LUNAR^® lipid-mediated delivery. The company remains domiciled in Israel subsequent to the merger described herein. Reverse Merger On November 15, 2017, Alcobra Ltd. acquired Arcturus Therapeutics, Inc. pursuant to a merger between the companies (the “merger”). Prior to the merger, Alcobra Ltd.’s net assets consisted of cash, investments and nominal non-operating assets. Upon consummation of the merger, Alcobra Ltd. adopted the business plan of Arcturus Therapeutics, Inc. In connection with the merger, Alcobra Ltd. agreed to acquire all of the outstanding common stock of Arcturus Therapeutics, Inc. in exchange for the issuance of an aggregate 6,631,712 of Alcobra Ltd.’s Ordinary Shares, par value 0.07 NIS per share (the “Ordinary Shares”), after giving effect to a 1-for-7 reverse split effected immediately prior to the merger. As a result of the merger, Arcturus Therapeutics, Inc. became a wholly-owned subsidiary of Alcobra Ltd. While Alcobra Ltd. was the legal acquirer in the transaction, Arcturus Therapeutics, Inc. was deemed the accounting acquirer. Immediately after giving effect to the merger, on November 15, 2017, Alcobra Ltd. changed its name to Arcturus Therapeutics Ltd. (“Arcturus” or the “Company”). On November 16, 2017, the Company commenced trading under the symbol “ARCT.” The Company’s principal executive offices are located in San Diego, California. In accordance with the authoritative literature, a transaction where a private company merges into a public company with no operations and nominal net assets should be accounted for as a capital transaction rather than a business combination. Consequently, the reverse merger was accounted for as an issuance of shares by the Company for the net assets of Alcobra Ltd., accompanied by a recapitalization. Excess of considerations paid over net assets acquired and other merger-related costs were recorded as a charge to additional paid-in capital as discussed in Note 6. While Alcobra Ltd. was the legal acquirer in the merger, Arcturus was deemed the accounting acquirer. As a result, the financial statements of the Company prior to the merger date are the historical financial statements of Arcturus whereas the financial statements of the Company after the merger date reflect the results of the operations of Arcturus and Alcobra Ltd. on a combined basis. All historical information presented herein has been retroactively restated to reflect the effect of the merger shares exchange ratio, reverse stock split and change to the authorized number of Ordinary Shares in accordance with Accounting Standards Codification Topic 260, “Earnings Per Share”. Liquidity The Company’s activities since inception have consisted principally of performing research and development activities and raising capital. The Company’s activities are subject to significant risks and uncertainties, including failing to secure additional funding before the Company achieves sustainable revenues and profit from operations. Historically, the Company’s primary source of financing has been through the sale of its securities, through issuance of convertible promissory notes and through collaboration agreements. Research and development activities have required significant capital investment since the Company’s inception. We expect our operations to continue to require cash investment to pursue the Company’s research and development activities, including preclinical studies, formulation development, clinical trials and related drug manufacturing. The Company has a limited operating history, and is preclinical with no revenues from sales of its products, and the sales and income potential of the Company’s business and market are unproven. The Company has experienced net losses since its inception and as of December 31, 2017 has an accumulated deficit of $23.1 million . The Company acquired $36.4 million in cash, cash equivalents and short-term investments in conjunction with the merger, however, the Company expects to continue to incur additional losses for the next several years, and over that period the Company may need to raise additional debt or equity financing or enter into additional partnerships to fund its development. The ability of the Company to transition to profitability is dependent on developing products and product revenues to support the level of expenses. If the Company is not able to achieve its planned revenue growth or incurs costs in excess of its forecasts, it may be required to reduce discretionary spending, may not be able to continue the development of all of its products or may be required to delay part of its development programs, which could have a material adverse effect on the Company’s ability to achieve its intended business objectives. There can be no assurances that additional financing will be secured or, if secured, will be on favorable terms. The Company's management and board of directors are of the opinion that its current financial resources will be sufficient to continue the development of the Company's products for at least twelve months from the filing of this Annual Report. In order to support our long-term plans, we intend to seek additional capital through equity and/or debt financings, collaborative or other funding arrangements with partners or through other sources of financing. Should we seek additional financing from outside sources, we may not be able to raise such financing on terms acceptable to us or at all. If we are unable to raise additional capital when required or on acceptable terms, we may be required to scale back or discontinue the advancement of product candidates, reduce headcount, liquidate our assets, file for bankruptcy, reorganize, merge with another entity, or cease operations. If we are unable to maintain sufficient financial resources, our business, financial condition and results of operations will be materially and adversely affected. There can be no assurance that the Company will be able to obtain the needed financing on acceptable terms or at all.

Summary of Significant Accounting Policies

12 Months Ended

Dec. 31, 2017

Accounting Policies [Abstract]

Summary of Significant Accounting Policies

NOTE 2. Summary of Significant Accounting Policies

Basis of Presentation and Principles of Consolidation

The accompanying consolidated financial statements include the accounts of Arcturus Therapeutics Ltd. and its subsidiaries. All intercompany accounts and transactions have been eliminated in consolidation. These financial statements are prepared in conformity with accounting principles generally accepted in the United States (U.S. GAAP), which requires management to make estimates and assumptions regarding the valuation of certain debt and equity instruments, the intangible asset, share-based compensation, accruals for liabilities, income taxes, revenue and deferred revenue, expense accruals, and other matters that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of revenues and expenses during the reporting period. In the opinion of management, all adjustments, consisting of normal recurring accruals and other adjustments related to our merger, considered necessary for a fair presentation have been included. Actual results could materially differ from those estimates.

Segment Information

Operating segments are identified as components of an enterprise about which separate discrete financial information is available for evaluation by the chief operating decision-maker in making decisions regarding resource allocation and assessing performance. The Company and its chief operating decision-maker view the Company’s operations and manage its business in one operating segment which is the research and development of medical applications for our nucleic acid-focused technology.

Reclassification of Prior Year’s Presentation

Certain prior year amounts have been reclassified for consistency with the current period presentation. This reclassification had no effect on the reported results of operations.

Foreign Currency Translation

The functional currency of the Company is the U.S. dollar. Monetary accounts maintained in currencies other than the dollar are remeasured into U.S. dollars in accordance with Accounting Standards Codification (“ASC”) Topic 830, “Foreign Currency Matters”. Translation gains or losses were immaterial for the years ended December 31, 2017, 2016 and 2015.

Cash and Cash Equivalents

Cash equivalents are short-term highly liquid investments that are readily convertible to cash with original maturities of three months or less at the date of purchase to be cash equivalents.

Restricted cash

Restricted cash represents cash required to be set aside as security for lease payments and to maintain a letter of credit for the benefit of the landlord for the Company’s offices. At December 31, 2017, the Company had restricted cash of $166,000 and $107,000 in conjunction with property leases in Israel and San Diego, California, respectively. The restricted cash related to the Israel facility is classified as current as it expected to be received by the Company within 12 months. The restricted cash related to the San Diego facility is included in the balance of other assets and classified as a non-current asset as it is expected to be received at the end of the lease term in 2025. There was no restricted cash at December 31, 2016.

Short-term Bank Deposits

Short-term bank deposits are deposits with maturities of more than three months and up to one year when acquired. Short-term bank deposits are presented at their cost, including accrued interest and are included in the balance of short-term investments in the consolidated balance sheet.

Short-term Investments

The Company accounts for short-term investments in accordance with ASC No. 320, Investments- Debt and Equity Securities. Management determines the appropriate classification of its investments at the time of purchase and reevaluates such determinations at each balance sheet date.

The Company has classified all of its debt securities and certificates of deposit as available-for-sale securities. Available-for-sale securities are carried at fair value, with the unrealized gains and losses reported in accumulated other comprehensive (gain)loss in shareholders' equity (deficit). Realized gains and losses on sales of investments are included in interest income and are derived using the specific identification method for determining the cost of securities.

The amortized cost of debt securities is adjusted for amortization of premiums and accretion of discounts to maturity. Such amortization together with interest and dividends on securities are included in interest income.

The Company recognizes an impairment charge when a decline in the fair value of its investments in securities below the amortized cost basis of such securities is judged to be other-than-temporarily impaired. Factors considered in making such a determination include the duration and severity of the impairment, the reason for the decline in value, the potential recovery period and if the entity has the intent to sell the security, or if it is more likely than not that it will be required to sell the security before recovery of its amortized cost basis. The Company did not recognize any other-than-temporary impairment charges on its marketable securities during the years ended December 31, 2017, 2016 or 2015.

Fair Value Measurements

Fair value is defined as the exit price, or the amount that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants as of the measurement date. A hierarchy has been established for inputs used in measuring fair value that maximizes the use of observable inputs and minimizes the use of unobservable inputs by requiring that the most observable inputs be used when available.

Observable inputs are inputs market participants would use in valuing the asset or liability developed based on market data obtained from sources independent of the Company. Unobservable inputs are inputs that reflect the Company’s assumptions about the factors market participants would use in valuing the asset or liability developed based upon the best information available under the circumstances. The hierarchy is broken down into three levels. Level 1 inputs are quoted prices (unadjusted) in active markets for identical assets or liabilities. Level 2 inputs include quoted prices for similar assets or liabilities in active markets, quoted prices for identical or similar assets or liabilities in markets that are not active, and inputs (other than quoted prices) that are observable for the asset or liability, either directly or indirectly. Level 3 inputs are unobservable inputs for the asset or liability. Categorization within the valuation hierarchy is based upon the lowest level of input that is significant to the fair value measurement.

Accounts Receivable

Accounts receivable are recorded at the net invoice value and are non-interest bearing. The Company considers receivables past due based on the contractual payment terms. The Company reserves specific receivables if collectability is no longer reasonably assured. Estimates for allowances for doubtful accounts are determined based on existing contractual obligations, historical payment patterns, and individual customer circumstances. The Company reevaluates such reserves on a regular basis and adjusts its reserves as needed. Once a receivable is deemed to be uncollectible, such balance is charged against the reserve. No reserves have been recorded as of December 31, 2017 or 2016.

Concentration of Credit Risk and Significant Customers

The Company is exposed to credit risk from cash and investment balances at banks in excess of amounts insured by the Federal Deposit Insurance Corporation, including deposits held in two large banks located in Israel and by a U.S. based brokerage. The Company mitigates its exposure by investing in certificates of deposit in banks that have a credit rating of at least Baa1/BBB+ and corporate debentures that carry a rating of at least A2/A. The Company’s investment policy is approved by the Board of Directors and limits the amount that the Company may invest in any one type of investment or issuer, thereby reducing credit risk concentrations. The Company has not experienced any losses on deposits since inception.

There was one customer that comprised the total accounts receivable balance at December 31, 2017. One customer individually represented 88% of the Company’s accounts receivable balance at December 31, 2016.

For the year ended December 31, 2017, there were three customers that collectively represented 92% of the Company’s total revenue. For the years ended December 31, 2016 and 2015, there were two customers that represented 95% and 99% of the Company’s total revenue, respectively.

Intangible asset held for sale

The Company’s intangible asset represents capitalized in-process research and development (IPR&D) acquired in conjunction with the merger in 2017 (see Note 6 to the consolidated financial statements).

Property and Equipment, net

Property and equipment are stated at cost, net of accumulated depreciation and amortization. The cost of property and equipment is depreciated or amortized using the straight-line method over the respective useful lives of the assets, ranging from three to five years. Leasehold improvements are amortized using the straight-line method over the shorter of the estimated useful life of the asset or the lease term. Long-lived assets, including property and equipment are reviewed for impairment whenever events or circumstances indicate that the carrying amount of these assets may not be recoverable. The determinants used for this evaluation include management’s estimate of the asset’s ability to generate positive income from operations and positive cash flow in future periods, as well as the strategic significance of the assets to the Company’s business objectives. The Company did not recognize any impairment losses for the years ended December 31, 2017, 2016 or 2015.

Comprehensive Loss

Comprehensive loss is defined as the change in equity during a period from transactions and other events and circumstances from non-owner sources. Comprehensive loss represents unrealized losses on the Company’s marketable securities. The income tax effect related to unrealized losses was immaterial for December 31, 2017.

Revenue Recognition

The Company enters into arrangements with pharmaceutical and biotechnology partners that may involve multiple deliverables. The Company’s arrangements may contain upfront payments, license fees for research and development arrangements, research and development funding or reimbursement, milestone payments, option fees, exclusivity fees and royalties on future sales of our products. Each deliverable in the arrangement is evaluated at the inception of the arrangement to determine whether it meets the criteria to be accounted for as a separate unit of accounting or whether it should be combined with other deliverables. When deliverables are separable, consideration received is allocated to the separate units of accounting based on the relative selling price method and the appropriate revenue recognition principles are applied to each unit. Revenue is recognized separately for each unit of accounting when all four of the following criteria are met: (i) persuasive evidence that an arrangement exists; (ii) delivery of the products and/or services has occurred; (iii) the selling price is fixed or determinable; and (iv) collectability is reasonably assured. Deliverables in an arrangement that do not meet this separation criteria are treated as a single unit of accounting, generally applying applicable revenue recognition guidance for the final deliverable to the combined unit of accounting. In the instances in which the Company has received payment from customers in advance of recognizing revenue, the Company records the amounts as deferred revenue on the consolidated balance sheet. Amounts not expected to be recognized within the next 12 months are classified as non-current deferred revenue. As discussed further under Note 3, Strategic Alliances and Collaboration Agreements, total deferred revenue for the year ended December 31, 2017 and 2016 was comprised of $7.6 million and $0.4 million for Collaboration Partner A, respectively; $5.8 million and $6.2 million for Collaboration Partner B, respectively; negligible amount and $0.2 million for Collaboration Partner C, respectively; and $0.2 million and $0.8 million for Other, respectively. Deferred revenue includes unamortized upfront fees under these collaboration agreements.

Funded Research. Some of the Company’s research and development costs are funded or reimbursed by partners in accordance with collaboration agreements. Amounts received as compensation related to the Company’s research and development efforts are recognized as revenue when the above criteria have been met.

Upfront Fees. When the Company determines that deliverables in an arrangement do not meet the separation criteria discussed above, the deliverables are treated as a single unit of accounting. In such cases, upfront fees received for collaborative agreements are recognized on a straight-line basis, unless evidence suggests that the revenue is earned or obligations are fulfilled in a different pattern, over the expected performance period under each respective arrangement. When the performance period is not specified, the Company makes its best estimate of the period over which the Company expects to fulfill its performance obligations under an arrangement. Any amounts received under the arrangement in advance of performance are recorded as deferred revenue and recognized as revenue as the Company completes its performance obligations.

Milestones. The Company applies the milestone method of accounting to recognize revenue from milestone payments when earned, as evidenced by written acknowledgement from the collaborator or other persuasive evidence that the milestone has been achieved and the payment is non-refundable, provided that the milestone event is substantive. A milestone event is defined as an event (i) that can only be achieved based in whole or in part on either our performance or on the occurrence of a specific outcome resulting from our performance; (ii) for which there is substantive uncertainty at the inception of the arrangement that the event will be achieved; and (iii) that would result in additional payments being due to the Company. Events for which the occurrence is either contingent solely upon the passage of time or the result of a counterparty’s performance are not considered to be milestone events. A milestone event is substantive if all of the following conditions are met: (i) the consideration is commensurate with either the Company’s performance to achieve the milestone, or the enhancement of the value to the delivered item(s) as a result of a specific outcome resulting from the Company’s performance to achieve the milestone; (ii) the consideration relates solely to past performance; and (iii) the consideration is reasonable relative to all the deliverables and payment terms (including other potential milestone consideration) within the arrangement.

The Company assesses whether a milestone is substantive at the inception of each arrangement. If a milestone is deemed non-substantive, the Company will account for that milestone payment using a method consistent with the related units of accounting for the arrangement over the estimated performance period.

Research and Development Costs, net

Research and development costs are expensed as incurred. Non-refundable advance payments are expensed when services are initiated. These expenses result from the Company's independent research and development efforts as well as efforts associated with collaboration arrangements. Research and development costs include salaries and personnel-related costs, consulting fees, fees paid for contract research and manufacturing services, the costs of laboratory supplies, equipment and facilities and other external costs are shown net of any royalty bearing grants.

Royalty Bearing Grant

Royalty-bearing grants from Cystic Fibrosis Foundation Therapeutics, Inc. (CFFT) amounted to $0.3 million and $0.2 million during the years ended December 31, 2017 and 2016, respectively. Royalty-bearing grants from CFFT for certain research and development projects are recognized on the basis of related costs incurred, and are included as a deduction from research and development expenses.

Share-Based Compensation

The Company recognizes share-based compensation for equity awards granted to employees, officers, and directors as an expense on the statements of operations. Share-based compensation is recognized over the requisite service period of the individual awards, which generally equals the vesting period. Share options have a ten-year life and generally vest 25% on the first anniversary of the grant and in 1/48th equal installments on each monthly anniversary thereafter, such that options are fully vested on the four-year anniversary of the date of grant.

The fair value of share options is estimated using a Black-Scholes valuation model on the date of grant. This method requires certain assumptions be used as inputs, such as the fair value of the underlying common shares, expected term of the option before exercise, expected volatility of the Company’s Ordinary Shares, expected dividend yield, and a risk-free interest rate. The Company has limited historical share option activity and therefore estimates the expected term of share options granted using the simplified method, which represents the average of the contractual term of the share option and its weighted-average vesting period. The expected volatility of share options is based upon the historical volatility of a number of publicly traded companies in similar stages of clinical development. We have not declared or paid any dividends and do not currently expect to do so in the foreseeable future. The risk-free interest rates used are based on the implied yield currently available in United States Treasury securities at maturity with a term equivalent to the expected term of the share options. The effect of forfeited awards is recorded when the forfeiture occurs.

Share-based awards to non-employees are remeasured at each reporting date and compensation costs are recognized as services are rendered, generally on a straight-line basis. The Company believes that the fair value of these awards is more reliably measurable than the fair value of the services rendered.

Ordinary Shares Valuation

Prior to the merger and due to the absence of an active market for the Company’s ordinary shares, the Company utilized third-party valuations which utilized methodologies in accordance with the framework of the American Institute of Certified Public Accountants Technical Practice Aid, Valuation of Privately-Held Company Equity Securities Issued as Compensation, to estimate the fair value of its Ordinary Shares.

Prior to 2017, the income and market approach and the Option-Pricing-Method, as appropriate, were used to value the Ordinary Shares of the Company at the option grant dates. A discount for lack of marketability was also incorporated in determining the value of the Ordinary Shares.

During 2017, the Company relied on the Guideline Transaction Method (Return on Invested Capital) to estimate the value the Ordinary Shares of the Company at the option grant dates. The Company conducted a search for development stage and preclinical trials stage biotechnology therapeutics companies which initially received capital and later were acquired in merger and acquisitions transactions. Under this method, the Company estimated its range of business enterprise value (“BEV”).

Similar Transactions: The Company conducted a search for development stage and preclinical trials stage biotechnology therapeutics companies using the Dow Jones VentureSource™ database of private venture-backed companies and selected private target companies similar to the Company.

Range of Multiple Observed: Using the total deal consideration and the total capital raised prior to the acquisition, the Company estimated the total deal consideration/capital raised multiple;

Multiples Selection: The Company selected multiples of 1.00x and 1.50x for the low and high estimates, respectively. The Company selected multiples between the minimum and lower (first) quartile of the dataset due to the Company's stage of product development and the inherent survivorship bias of the dataset. These multiplies were applied to the Company’s total productive invested capital as of the Valuation Date.

Discount for Lack of Control (“DLOC”): The BEV range estimated from the Guideline Transaction Method reflects a controlling interest. In order to estimate a BEV on a minority interest basis, the Company applied a discount for lack of control to the indicated equity value after accounting for any debt.

After estimating a range of BEV, the Company added cash and cash equivalents to derive an estimated range of the Market Value of Invested Capital (“MVIC”). The Company than adjusted this value for debt and estimated the value of the Company’s equity.

After estimating the Company’s equity value, the Company allocated the value to the various equity classes and debt comprising the Company’s capitalization table using the Option-Pricing Method. Under the OPM, each equity class was modeled as having a call option with a distinct claim on the total value of the Company. Each option’s exercise price was based on the Company’s total value available for each participating security holder. The characteristics of each class of ownership determined the claim on the total value for that class of ownership. By constructing a series of options in which the exercise prices were set at incremental levels of value corresponding to the values necessary for each level of equity to participate, we determined the incremental option value of each series. When multiplied by the percentage of ownership of each equity class participating under that series, the result was the incremental value allocated to each class under that series. The Company used the Black Scholes option-pricing model within the equity allocation.

In making the final determination, the Company determined a discount for lack of marketability.

For awards issued near the merger date, a market approach was utilized based upon publicly available prices for Alcobra Ltd. Significant changes to the key assumptions underlying the factors used could have resulted in different fair values of ordinary shares at each valuation date.

Statement of cash flows

The following table provides a reconciliation of cash and cash equivalents and restricted cash reported within the balance sheet to the total of the same such amounts shown in the statement of cash flows:

	As of December 31,
(in thousands)	2017		2016		2015
Cash and cash equivalents	$	24,965	$	8,345	$	11,894
Restricted cash		166		-		-
Restricted cash (included in other assets)		107		-		-
Total cash, cash equivalents and restricted cash shown in the statement of cash flows	$	25,238	$	8,345	$	11,894

Income Tax Expense

The Company records deferred tax assets and liabilities for the expected future tax consequences of temporary differences between the Company’s financial statement carrying amounts and the tax basis of assets and liabilities using enacted tax rates expected to be in effect in the years in which the differences are expected to reverse. A valuation allowance is provided to reduce the net deferred tax assets to the amount that will more likely than not be realized. The effect of a change in tax rates on deferred tax assets and liabilities is recognized in the provision for income taxes in the period that includes the enactment date.

The Company also assesses the probability that the positions taken or expected to be taken in its income tax returns will be sustained by taxing authorities. A “more likely than not” (more than 50 percent) recognition threshold must be met before a tax benefit can be recognized. Tax positions that are more likely than not to be sustained are reflected in the Company’s financial statements. Tax positions are measured as the largest amount of tax benefit that is greater than 50 percent likely of being realized upon settlement with a taxing authority that has full knowledge of all relevant information. The difference between the benefit recognized for a position and the tax benefit claimed on a tax return is referred to as an unrecognized tax benefit. Potential interest and penalties associated with such uncertain tax positions are recorded as a component of income tax expense.

Net Loss per Share

Basic net loss per share is calculated by dividing the net loss by the weighted-average number of Ordinary Shares outstanding for the period, without consideration for ordinary share equivalents. Diluted net loss per share is calculated by dividing the net loss by the weighted-average number of Ordinary Shares and dilutive ordinary share equivalents outstanding for the period determined using the treasury-stock method. Dilutive Ordinary Shares are comprised of convertible preferred stock, convertible notes, share options and warrants. Dilutive securities that were not included in the calculation of diluted net loss per share because they were anti-dilutive totaled 3,057,000, 2,800,000 and 3,843,000 potential shares at December 31, 2017, 2016 and 2015, respectively.

The calculation of the weighted-average number of shares outstanding excludes shares which have been issued upon the early exercise of share options and are subject to future vesting and unvested restricted stock totaling 702,000, 769,000 and 769,000 shares as of December 31, 2017, 2016 and 2015, respectively, and shares held in treasury totaling 43,000 at December 31, 2017. There were no treasury shares at December 31, 2016 or 2015.

The Company applies the two-class method as required by ASC Topic 260-10, “Earnings Per Share” (“ASC 260-10”), which requires the income or loss per share for each class of shares (ordinary and preferred shares) to be calculated assuming 100% of the Company’s earnings are distributed as dividends to each class of shares based on their contractual rights.

No dividends were declared or paid during the reported periods. According to the provisions of ASC 260-10, the Company’s preferred shares are not participating securities in losses and, therefore, are not included in the computation of net loss per share.

Recently Issued Accounting Pronouncements

In May 2014, the Financial Accounting Standards Board (FASB) amended the existing Accounting Standards Update (ASU) for revenue recognition No. 2014-09, Revenue from Contracts with Customers, which outlines a comprehensive revenue recognition model and supersedes most current revenue recognition guidance. ASU 2014-09 outlines a five-step process for revenue recognition that focuses on transfer of control, as opposed to transfer of risk and rewards, and also requires enhanced disclosures regarding the nature, amount, timing and uncertainty of revenues and cash flows from contracts with customers. Major provisions include determining which goods and services are distinct and require separate accounting (performance obligations), how variable consideration (which may include change orders and claims) is recognized, whether revenue should be recognized at a point in time or over time and ensuring the time value of money is considered in the transaction price.

The FASB subsequently issued amendments to ASU No. 2014-09 that have the same effective date and transition date. Due to the Company’s emerging growth company status, these new standards will become effective for the Company on January 1, 2019. This ongoing evaluation is dependent upon the resolution of certain questions relating to the application of the new revenue recognition guidance for collaboration agreements which will ultimately determine the impact, if any, the adoption of this standard may have on our financial statements.

In February 2016, the FASB issued ASU 2016-02, Leases, which outlines a comprehensive lease accounting model and supersedes the current lease guidance. The new accounting standard requires lessees to recognize lease liabilities and corresponding right-of-use assets for all leases with lease terms of greater than twelve months. It also changes the definition of a lease and expands the disclosure requirements of lease arrangements. The new accounting standard must be adopted using the modified retrospective approach and is effective for entities for annual reporting periods beginning after December 15, 2018, with early adoption permitted. Since the Company’s emerging growth company status will cease at December 31, 2018, this standard will become effective for the Company on January 1, 2019. The Company is currently evaluating the impact that the adoption of ASU 2016-02 will have on its consolidated financial statements and related disclosures.

Recently Adopted Accounting Pronouncements

Effective January 1, 2017, the Company adopted ASU No. 2017-09 Compensation – Stock Compensation (Topic 718): Scope of Modification Accounting (ASU No. 2017-09). ASU No. 2017-09 provides guidance about which changes to the terms or conditions of a share-based payment award require an entity to apply modification accounting. The Company’s adoption of ASU No. 2017-09 had no impact on the Company’s statements of financial position or results of operations and comprehensive loss.

In November 2016, the FASB issued ASU 2016-18, Restricted Cash, which requires entities to show the changes in the total of cash, cash equivalents, restricted cash and restricted cash equivalents in the statement of cash flows. As a result, entities will no longer present transfers between cash and cash equivalents and restricted cash and restricted cash equivalents in the statement of cash flows. This update is effective for annual periods beginning after December 15, 2017, and interim periods within those fiscal years with early adoption permitted. The Company adopted this pronouncement retrospectively effective in the December 31, 2017 consolidated financial statements. There was no effect on previously reported balances as a result of adoption of the standard.

In January 2017, the FASB issued ASU 2017-01, Business Combinations (Topic 805): “Clarifying the Definition of a Business” which clarifies the definition of a business and affects all companies and other reporting organizations that must determine whether they have acquired or sold a business. The amendments are intended to assist with the evaluation of whether transactions should be accounted for as acquisitions (or disposals) of assets or businesses. The guidance is effective for the Company for fiscal years beginning after December 15, 2018, and interim periods within those fiscal years and should be applied prospectively as of the beginning of the period of adoption. Early adoption is permitted under certain circumstances. The Company adopted ASU 2017-01 as of January 1, 2017 and the adoption did not have an impact on the Company’s accounting and disclosures.

Strategic Alliances and Collaboration Agreements

12 Months Ended

Dec. 31, 2017

Collaboration Agreements [Abstract]

Strategic Alliances and Collaboration Agreements

NOTE 3. Strategic Alliances and Collaboration Agreements

The Company has entered into license agreements and collaborative research and development arrangements with pharmaceutical and biotechnology companies. Under these arrangements, the Company is entitled to receive license fees, upfront payments, milestone payments when and if certain research or technology transfer milestones are achieved, development milestones and reimbursement for research and development activities. The Company's costs of performing these services are included within research and development expense. The Company’s milestone payments are typically defined by achievement of certain preclinical, clinical, and commercial success criteria. Preclinical milestones may include in vivo proof of concept in disease animal model(s), lead candidate identification, and completion of IND-enabling studies. Clinical milestones may include successful enrollment of the first patient in or completion of Phase I, II, and III clinical trials, and commercial revenue is often tiered based on net or aggregate sale amounts. The Company cannot guarantee the achievement of these milestones due to risks associated with preclinical and clinical activities required for development of nucleic acid medicine-based therapeutics.

The following table summarizes our revenues under strategic alliances and collaborations for the periods indicated (in thousands):

	Year Ended December 31,
(Dollars in thousands)	2017		2016		2015
Collaboration Partner A	$	4,862	$	12,008	$	5,123
Collaboration Partner B		5,639		7,395		979
Collaboration Partner C		1,403		28		-
Other		1,094		951		36
Total	$	12,998	$	20,382	$	6,138

The following paragraphs provide information on the nature and purpose of these collaboration arrangements.

Collaboration Partner A

In 2015 the Company entered into two agreements with Collaboration Partner A. The Company analyzed the form and substance of both of the agreements and concluded they should be evaluated as a single arrangement for accounting purposes.

The Company concluded that the license, research and development activities, exclusivity, and joint steering committed obligations under this collaboration should be considered a single unit of accounting in the arrangement and the up-front fee was deferred and was initially being recognized as revenue ratably over the expected 23-month period of the research activities. In 2016, the parties agreed to extend the period of performance of the research term by an additional 6 weeks and the Company correspondingly updated the amortization period of the remaining deferred revenue. The Company also reached certain milestones in 2015 and in 2016 that were determined, as of the inception of the agreement, to be substantive and the revenue related to these milestones was recognized when they were achieved.

As a result of the mid-2017 termination of the 2015 collaboration, the remaining deferred revenue associated with the upfront, non-refundable payment was recognized as revenue since all performance obligations associated with the 2015 agreement had been completed by the Company. Further, the Company recognized revenue of $4.9 million, $12.0 million, and $5.1 million during the years ended December 31, 2017, 2016 and 2015, respectively, primarily under the 2015 agreement. The revenue recognized included labor and expense reimbursements of $4.4 million, $9.5 million and $3.0 million, December 31, 2017, 2016 and 2015, respectively, with the remaining revenue representing the amortized portion of the upfront fee and milestone payment on the arrangement.

In late-2017, the Company and Collaboration Partner A entered into a new agreement. The Company reviewed the timing and nature of the arrangement upon the signing of the new agreement and determined that it was not linked to the prior agreements and should be considered as a standalone agreement.

The 2017 collaboration allocated discovery, development, funding obligations, and ownership of related intellectual property among the Company and Collaboration Partner A, with Collaboration Partner A making an upfront payment, and potential milestone payments and royalty payments to the Company. The Company received an upfront payment and may receive preclinical, development and sales milestone payments, as well as royalty payments on any future licensed product sales. Collaboration Partner A will reimburse the Company for development costs at a future defined period upon the achievement of the first research and development milestone and all commercialization costs associated with the program upon selection of a drug target. The 2017 collaboration agreement includes potential milestone payments from the Collaboration Partner A to the Company of $56.5 million. Collaboration Partner A may also pay option exercise fees within the $1.0 million to $5.0 million range per target. Collaboration Partner A will pay royalties on annual net sales of licensed products in the low to mid-single digits range, subject to reduction on a country-by-country and licensed-product-by-licensed-product basis and subject to certain events, such as expiration of program patents. In addition, the collaboration includes an exclusivity period.

As the license component of the contract has no stand-alone value, the license and the research and development activities, exclusivity, and joint steering committee obligations under this agreement should be considered as a single unit of accounting in the arrangement. The upfront fee will be deferred and recognized as revenue using the Proportional Performance Method as the Company determined that the performance obligations are fulfilled in a pattern other than straight-line due to the structure and nature of the collaborative arrangement. During the year-end December 31, 2017 the Company recognized an negligible amount related to the 2017 agreement for Collaboration Partner A.

Collaboration Partner B

In 2015 the Company entered into an agreement with Collaboration Partner B. During the initial phase of the collaboration, the Company will design and optimize therapeutics for certain rare disease targets. Collaboration Partner B has the option to add additional rare disease targets during the collaborative development period. Additionally, during the collaborative development period, the Company will participate with Collaboration Partner B in a joint steering committee. In addition, the collaboration includes an initial exclusivity period and an option to extend this period.

For each program, Collaboration Partner B will reimburse the Company for all internal and external development costs incurred and if Collaboration Partner B achieves certain, clinical, regulatory and sales milestones, then the Company is eligible to receive additional payments.

As part of the agreement, Collaboration Partner B paid an upfront fee and agreed to certain research and development funding obligations. The Company is also entitled to certain additional payments upon exercise of the Collaboration Partner B expansion option and/or exclusivity extension (if any), and for costs incurred by us in conducting the activities assigned to us under each collaboration development plan. In addition, on a development target-by-development target basis during the two-year period from the effective date of contract, Collaboration B will pay the Company a one-time milestone payment after the first optimized lead designation for the first product with respect of such development target. For each development target for which the Collaboration Partner B exercises its option, Collaboration Partner B will pay the Company a one-time option exercise fee based upon on the total number of development targets for which option exercises have been made by Collaboration Partner B. Subsequent to year end December 31, 2017, the Company signed an amendment with Collaboration Partner B, that may reduce milestone payments dependent on whether the Company does not incorporate a predefined chemistry methodology.

The agreement included total potential milestone payments for the initially selected targets from the Collaboration Partner B to the Company of $133.0 million. Collaboration Partner B will pay royalties as a percentage of net sales on a product-by-product and country-by-country basis during the applicable royalty term up to 10%. As of December 31, 2017, the Company has not yet reached the clinical phase of the contract.

The Company concluded that the license, research and development activities, exclusivity, and joint steering committed obligations under this agreement should be considered a single unit of accounting in the arrangement, the up-front fee will be deferred and recognized as revenue over the same period as the research activities. As a result, the upfront fee has been deferred and was initially being recognized as revenue ratably over the expected 29-month period of the research activities and was adjusted by an additional 11 months and 19 months during 2016 and 2017, respectively. As such, the Company updated the amortization period of the remaining deferred revenue.

The Company also determined that the milestone payments as defined in the agreement were not substantive as it will not have any outstanding performance obligations under the agreement when such payments may become due, and, therefore, do not meet the requirements for application of the Milestone Method of revenue recognition. Instead, revenue from the contingent milestone payments will be recognized if and when such payments become due, subject to satisfaction of all of the criteria necessary to recognize revenue at that time.

During 2017, the Company entered into an amendment with Collaboration Partner B to add one year to the exclusivity period for the two initial targets, in consideration for a one-time payment of $2.0 million. The extension of the exclusivity period did not change the length of the research and development period. Further, the amendment added language to allow Collaboration Partner B the opportunity to review and comment on its filings and prosecution efforts of pending Company Patents that relate to Collaboration Partner B Chemistry. Since the Company's performance obligations under the agreement are considered a single unit of accounting, the payment consideration was added to the unamortized portion of the upfront signing fee and recognized systematically, on a straight-line basis, over the remainder of the period that the research and development services are expected to occur.

The Company recognized revenue for Collaboration Partner B of $5.6 million, $7.4 million, and $1.0 million during the years ended December 31, 2017, 2016 and 2015, respectively. The revenue recognized included labor and expense reimbursements of $3.7 million, $3.8 million and $0.3 million, December 31, 2017, 2016 and 2015, respectively, with the remaining revenue representing the amortized portion of the upfront fee on the arrangement.

Collaboration Partner C

In 2016 the Company entered into a contract with Collaboration Partner C to perform certain discovery and development of RNA medicines for treatment of a disease. The agreement provides a non-exclusive license of the Company’s technology to Collaboration Partner C for the 18 month research program term, and the Company will not engage in similar research or development activities for two years after the end of the research term. In 2017 the Company and Collaboration Partner C amended the agreement to extend the agreement research program scope and term of 18 months from the Original Agreement effective date to 12 months from the Amendment Date (through September 2018.) Under the Agreement, the results specifically related to improvements to the Company products are owned by the Company, while all other Research Program results are owned by Collaboration Partner C.

The Collaboration Partner C Agreement remains in effect until Collaboration Partner C no longer has payment obligations. Collaboration Partner C may terminate the Agreement upon sixty days written notice. As part of the agreement, Collaboration Partner C paid an upfront fee of $0.1 million upon contract execution and agreed to provide the Company with funding for the discovery and development costs. The agreement included immaterial milestone payments that were met during 2017. The agreement provides for $3.7 million in regularly scheduled research funding payments through 2018. In addition, Collaboration Partner C has an option to negotiate with the Company to obtain a non-exclusive, sub-licensable worldwide license to use the Company’s background technology and its owned collaboration results. The Option may be exercised by Collaboration Partner C with written notice to the Company any time for a period commencing on the Effective Date and ending on one hundred and eighty (180) days after the date of Collaboration C receipt of the Final Report. The terms and conditions of any such license shall be negotiated in good faith and agreed upon in writing between the parties within twelve 12 months after the exercise of the option by Collaboration Partner C.

The Company concluded that the research funding, exclusivity and license fees were to be accounted for as a single unit of accounting and the upfront license fees were deferred and recognized as revenue over the same period as the research activities. The Company recognized revenue from Collaboration Partner C of $1.4 million and a negligible amount for the years ended December 31, 2017 and 2016, respectively. The revenue recognized includes expense reimbursements that are recognized as revenue when incurred as per the terms of the agreement and milestone payments.

Other Collaboration Agreements

In 2016 the Company entered into several other smaller agreements and recorded revenue and deferred revenue consistent with the revenue recognition practices described in the significant accounting policies footnote. Additionally, see Note 14 Related Party for the related party collaboration agreement.

Short-term Investments

12 Months Ended

Dec. 31, 2017

Investments Debt And Equity Securities [Abstract]

Short-term Investments

NOTE 4. Short-term Investments

The Company’s short-term investments consist of short-term bank deposits and marketable securities. Bank deposits with maturities of more than three months but less than one year are included in short-term bank deposits. Short-term deposits are stated at cost which approximates market values. As of December 31, 2017, the Company's bank deposits totaled $15.0 million, are in U.S. dollars and bear interest at a weighted average annual interest rate of 1.6%. There were no short-term bank deposits held by the Company at December 31, 2016.

The following is a summary of short-term investments at December 31, 2017:

	December 31, 2017
(Dollars in thousands)	Amortized cost		Gross unrealized gains		Gross unrealized losses			Fair value
Certificates of deposit	$	1,462	$	-	$	-		$	1,462
Corporate debt securities		7,149		-		(3	)		7,146
Total	$	8,611	$	-	$	(3	)	$	8,608

All short-term investments are held as available-for-sale and mature within twelve months of December 31, 2017. Management reviews unrealized losses individually and in the aggregate at each reporting period and has determined that none the balances are other than temporarily impaired based upon the brief duration of time that the investments have been at a loss position as of December 31, 2017. The Company had no short-term investments at December 31, 2016.

Fair Value Measurements

12 Months Ended

Dec. 31, 2017

Fair Value Disclosures [Abstract]

Fair Value Measurements

NOTE 5. Fair Value Measurements

The Company establishes the fair value of our assets and liabilities using the price that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date. The Company established a fair value hierarchy based on the inputs used to measure fair value.

The three levels of the fair value hierarchy are as follows:

Level 1: Quoted prices in active markets for identical assets or liabilities.

Level 2: Inputs, other than the quoted prices in active markets, that are observable either directly or indirectly.

Level 3: Unobservable inputs in which little or no market data exists, and are therefore determined using estimates and assumptions developed by the Company, which reflect those that a market participant would use.

The carrying value of cash, restricted cash, short-term bank deposits, accounts receivable, accounts payable, and accrued liabilities approximate their respective fair values due to their relative short maturities.

The following table presents our fair value hierarchy for assets measured at fair value on a recurring basis as of December 31, 2017 (in thousands):

	December 31, 2017
	Fair value measurements using input type
	Level 1		Level 2		Level 3		Total
Cash equivalents	$	2,024	$	-	$	-	$	2,024
Certificates of deposit		-		1,462		-		1,462
Corporate debt securities		-		7,146		-		7,146
Total financial assets	$	2,024	$	8,608	$	-	$	10,632

There were no assets measured at fair value on a recurring basis at December 31, 2016.

The fair value of certain financial instruments was measured and classified within Level 1 of the fair value hierarchy based on quoted prices. Certain financial instruments classified within Level 2 of the fair value hierarchy include the types of instruments that trade in markets that are not considered to be active, but are valued based on quoted market prices, broker or dealer quotations, or alternative pricing sources with reasonable levels of price transparency.

Certain non-financial assets are measured at fair value, usually with Level 3 inputs including the discounted cash flow method or cost method, on a nonrecurring basis in accordance with authoritative guidance. These represent nonfinancial assets initially measured at fair value in connection with our merger. The Company utilized significant management judgment to forecast the occurrence of future equity events with a high probability of success using the market valuation method. In general, non-financial assets, including our intangible asset and property and equipment, are remeasured at fair value when there is an indication of impairment and are recorded at fair value only when any impairment is recognized.

- Definition

The entire disclosure for the fair value of financial instruments (as defined), including financial assets and financial liabilities (collectively, as defined), and the measurements of those instruments as well as disclosures related to the fair value of non-financial assets and liabilities. Such disclosures about the financial instruments, assets, and liabilities would include: (1) the fair value of the required items together with their carrying amounts (as appropriate); (2) for items for which it is not practicable to estimate fair value, disclosure would include: (a) information pertinent to estimating fair value (including, carrying amount, effective interest rate, and maturity, and (b) the reasons why it is not practicable to estimate fair value; (3) significant concentrations of credit risk including: (a) information about the activity, region, or economic characteristics identifying a concentration, (b) the maximum amount of loss the entity is exposed to based on the gross fair value of the related item, (c) policy for requiring collateral or other security and information as to accessing such collateral or security, and (d) the nature and brief description of such collateral or security; (4) quantitative information about market risks and how such risks are managed; (5) for items measured on both a recurring and nonrecurring basis information regarding the inputs used to develop the fair value measurement; and (6) for items presented in the financial statement for which fair value measurement is elected: (a) information necessary to understand the reasons for the election, (b) discussion of the effect of fair value changes on earnings, (c) a description of [similar groups] items for which the election is made and the relation thereof to the balance sheet, the aggregate carrying value of items included in the balance sheet that are not eligible for the election; (7) all other required (as defined) and desired information.

+ References + Details

Reverse Merger with Alcobra Ltd.

12 Months Ended

Dec. 31, 2017

Business Combinations [Abstract]

Reverse Merger with Alcobra Ltd.

NOTE 6. Reverse Merger with Alcobra Ltd.

As described in Note 1 “Organization”, the reverse merger completed between Arcturus and Alcobra Ltd. was accounted for as a issuance of shares by the Company for the net assets of Alcobra Ltd., accompanied by a recapitalization. Arcturus was considered the acquirer for accounting and financial reporting purposes and acquired the assets and assumed the liabilities of Alcobra Ltd., and Arcturus gained control of the combined company after the merger. The annual consolidated financial statements of the Company reflect the operations of the acquirer for accounting purposes together with a deemed issuance of shares, equivalent to the shares held by the former stockholders of the legal acquirer and a recapitalization of the equity of the accounting acquirer. The annual consolidated financial statements include the accounts of the Company since the effective date of the reverse capitalization and the accounts of Arcturus Therapeutics, Inc. since inception.

The following summarizes the estimated fair value of the assets and liabilities acquired at the date of the merger:


(in thousands)
Cash and cash equivalents	$	2,032
Restricted cash		179
Short-term investments		34,188
Prepaid and other assets		434
Property, plant and equipment – held for sale		29
Intangible asset-held for sale		590
Total assets acquired		37,452
Accounts payable and accrued expenses		(1,906	)
Net assets acquired	$	35,546

The estimated fair value of total considerations paid was $40,841,000 based on the shares and options of Alcobra Ltd. outstanding on the merger date as adjusted per the merger agreement of 3,997,000 multiplied by the closing price of $10.22 on the date of the merger. The excess of the fair value of the consideration paid over the fair value of the net assets acquired as detailed above was $5,295,000, which was recorded as a charge to additional paid in capital in the equity section of the balance sheet. The Company also incurred direct merger-related costs totaling $1,734,000, which offset proceeds received from the transaction and were recorded as a reduction to additional paid in capital in the Company’s consolidated balance sheet.

Assets acquired in the merger included an intangible asset consisting of in-process research and development for proprietary drug technology called ADAIR. At the closing date of the reverse merger, we entered into an agreement with Amiservice to which we agreed to transfer certain intellectual property related to ADAIR in exchange for a minority equity stake in a company to be formed by Amiservice for the purpose of acquiring the ADAIR assets. The agreement is subject to certain closing conditions that have not been met. The Company determined that the asset met the classification criteria as held for sale in accordance with related accounting guidance when acquired and remained held for sale at December 31, 2017. There was also property, plant and equipment acquired in the merger which has been sold as of December 31, 2017. To determine the fair value of the ADAIR asset, the Company utilized an independent valuation consultant who valued the asset using a market approach valuation method. In conjunction with this valuation, management judgment was required to forecast the occurrence of future events that would trigger the closing of the ADAIR sale agreement. The asset will be evaluated at each future reporting date to evaluate whether it continues to be held for sale and for any potential impairment of its carrying value.

Balance sheet details

12 Months Ended

Dec. 31, 2017

Balance Sheet Related Disclosures [Abstract]

Balance Sheet Details

NOTE 7. Balance sheet details

Prepaid expenses and other current assets consisted of the following as of December 31, 2017 and December 31, 2016:

	December 31,
(in thousands)	2017		2016
Prepaid expenses	$	704	$	242
Other current assets		355		111
Total	$	1,059	$	353

Accrued liabilities consisted of the following as of December 31, 2017 and December 31, 2016:

	December 31,
(in thousands)	2017		2016
Accrued compensation	$	1,812	$	369
Other accrued liabilities		981		692
Total	$	2,793	$	1,061

Property and Equipment, Net

12 Months Ended

Dec. 31, 2017

Property Plant And Equipment [Abstract]

Property and Equipment, Net

NOTE 8. Property and Equipment, Net

Property and equipment, net consisted of the following:

	December 31,
(in thousands)	2017			2016
Research equipment	$	1,620		$	1,495
Computers and software		97			98
Office equipment and furniture		255			255
Leasehold improvements		44			44
Total		2,016			1,892
Less accumulated depreciation and amortization		(967	)		(557	)
Property and equipment, net	$	1,049		$	1,335

Depreciation and amortization expense was $410,000, $294,000 and $192,000 for the years ended December 31, 2017, 2016 and 2015, respectively.

Convertible Promissory Notes	12 Months Ended
Convertible Promissory Notes	Dec. 31, 2017
Debt Disclosure [Abstract]
Convertible Promissory Notes	NOTE 9. Convertible Promissory Notes In 2014 and 2015, the Company sold unsecured convertible promissory notes to investors, including members of the Board of Directors and beneficial owners of more than 5% of our capital stock, in the aggregate principal amount of $5.9 million. The notes were amended to extend the maturity date to December 31, 2016 and gave the holders the option to elect repayment or conversion upon maturity. The notes carried interest at a rate of 5% per annum, with interest payments deferred until conversion or maturity. In December 2016, the Company and the holders of a majority of the outstanding principal amount of the notes, modified the conversion price upon maturity of the notes which was deemed to represent an induced conversion for accounting purposes. On December 31, 2016, the notes matured and holders of $5,670,000 in outstanding principal and $560,000 of accrued interest elected to convert their outstanding balance into 521,415 shares of Series A Preferred Stock. Upon conversion of the notes, the Company recorded debt conversion expense of $250,000 within other expense in the consolidated statement of operations and comprehensive loss. The holders of $135,000 in outstanding principal elected repayment. The holders of $120,000 in outstanding principal remained outstanding as of December 31, 2016. In March 2017, the maturity date of the notes that remained outstanding was extended to December 31, 2017. During 2017, the Company sold unsecured convertible promissory notes in the aggregate principal amount of $5,675,000. The notes were scheduled to mature on February 28, 2019 and contained conversion provisions upon specified events. The notes carried interest at a rate of 5% per annum, with interest payments deferred until conversion or maturity. In September 2017, the convertible note agreements were amended in order to include an automatic conversion and beneficial conversion feature upon the closing of the merger agreement. On November 15, 2017 and in connection with the merger, holders of all of the Company's convertible promissory notes converted $5,795,000 of principal value and $162,000 of accrued interest of into 616,824 Ordinary Shares at an average conversion rate of $10.19 per share. Additionally, the Company recognized additional expense of $348,000 as a result of the beneficial conversion feature received by the noteholders upon settlement per terms of the amended note agreements, which was charged to other expense included in the consolidated statements of operations and comprehensive loss. The Company recognized interest expense related to the notes of $150,000, $295,000 and $251,000 during the years ended December 31, 2017, 2016 and 2015, respectively.

Shareholders’ Equity	12 Months Ended
Shareholders’ Equity	Dec. 31, 2017
Stockholders Equity Note [Abstract]
Shareholders’ Equity	NOTE 10. Shareholders’ Equity Preferred stock Series Seed Preferred Stock In April 2013, the Company sold and issued in a private placement 1,284,402 shares of Series Seed Preferred (“SSP”) stock at $1.02 per share. Each share of SSP stock granted the investor 0.15 fully vested warrants to purchase shares of ordinary shares at a strike price of $1.02 per share over a term no longer than ten years from the date of issue . Series A Preferred Stock In December 2013 and January 2014, the Company sold and issued 959,641 shares of Series A Preferred stock at $5.46 per share in a private placement. Upon the December 2016 maturity of the Notes, holders of $6,228,989 in outstanding principal and accrued interest elected conversion of their Notes into 521,449 shares of Series A Preferred stock at prices per share ranging from $11.60 to $12.97. Conversion of Series Seed and Series A Preferred Stock On November 15, 2017, the 2,765,492 outstanding shares of Series Seed and Series A preferred stock converted into the same number of Ordinary Shares immediately prior to the closing of the merger. Warrants Warrants were issued in connection with the issuance of the SSP stock. As of December 31, 2016, there were 192,647 warrants outstanding to purchase shares of our Ordinary Shares at $1.02 per share. In 2017 and in conjunction with the merger, all outstanding warrants were exercised for 188,980 Ordinary Shares (after subtraction of shares for net exercise, when selected). The Company received proceeds of $160,000 in conjunction with the warrant exercises in 2017. Ordinary Shares Merger and reverse stock split The Company completed the merger with Alcobra Ltd. on November 15, 2017 as described in footnote 6 to the consolidated financial statements. In connection with the merger, all outstanding shares of Arcturus Therapeutics, Inc. were exchanged for the Company’s Ordinary Shares at a rate of .293 Ordinary Shares of the Company’s stock for each share of Arcturus Therapeutics, Inc. common stock. Also on November 15, 2017 and prior to and in connection with the merger, Alcobra Ltd. effected a 1-for-7 reverse stock split of Ordinary Shares and changed Ordinary Shares authorized to 30,000,000 shares. All historical information presented herein has been retroactively restated to reflect the effect of the merger exchange ratio, reverse stock split and change to the authorized number of Ordinary Shares in accordance with Accounting Standards Codification Topic 260, “Earnings Per Share”. Restricted Ordinary Shares In March 2013, the founders of the Company purchased 2,783,686 Ordinary Shares of stock for $0.0068 per share. Of the shares purchased, 1,538,353 were subject to a repurchase option whereby the Company has an option for two months after date of termination of service as to repurchase any or all of the unvested shares at the original purchase price per share. The repurchase option shall be deemed to be automatically exercised by the Company as of the end of the two-month period unless the Company notifies the purchaser that it does not intend to exercise its option. The shares will be vested (1) 25% after obtaining suitable siRNA license; (2) 25% after in vivo proof-of-concept achieved; (3) 25% after a regulatory agency new drug application (such as an Investigational New Drug application) is filed and accepted by the applicable regulatory agency; and (4) 25% after human biological proof-of-concept is achieved. The Company met the first two milestones during 2013 and 2014. In 2017, the ordinary shares purchase agreements were amended to clarify vesting conditions resulting in a modification expense being recorded related to one of the awards totaling $1,495,000. As of December 31, 2017 and 2016 there were 622,667 and 769,176 Ordinary Shares which unvested and were subject to the repurchase option, respectively.

Share-Based Compensation

12 Months Ended

Dec. 31, 2017

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Share-Based Compensation

NOTE 11. Share-Based Compensation

Arcturus Therapeutics, Inc. had one stock compensation plan prior to the merger, the 2013 Equity Incentive Plan (the “2013” Plan) which provides for the granting of options, warrants, restricted stock awards, restricted stock units, and other equity-based compensation to the Company’s directors, employees and consultants. In connection with the merger and as required in the 2013 Plan, all outstanding options in the 2013 Plan converted into options to purchase shares of Alcobra Ltd.’s Ordinary Shares, as renamed Arcturus Therapeutics Ltd., and the applicable share amounts and exercise prices were adjusted to reflect the exchange ratio. The 2013 Plan has been extinguished and no additional grants shall be made from the 2013 Plan. Options granted under the 2013 Plan generally expire ten years from the date of grant. There are no shares available for future issuance under the 2013 Plan at December 31, 2017.

Prior to the merger, Alcobra Ltd. granted options to officers, directors, advisors, management and other key employees through the 2010 Incentive Option Plan (the “2010 Plan"). Substantially all options that were outstanding under the 2010 Plan became fully vested upon the closing of the merger. The value of these options was included as a component of the purchase price recorded in conjunction with the merger. The number of shares subject to and the exercise prices applicable to these outstanding options were adjusted in connection with the 1- for- 7 reverse stock-split. Options granted under the 2010 Plan generally expire ten years from the date of grant. Upon merger, the 2013 Plan was assumed by the 2010 Plan and the Company intends for the 2010 Plan to be its primary stock compensation plan for future awards. The Company generally issues new shares upon option exercise. There are 465,558 shares available for future issuance under the 2010 Plan as of December 31, 2017.

Share Options

The following table presents the weighted-average assumptions used in the Black-Scholes valuation model by the Company in calculating the fair value of share options granted:

	For the Year Ended December 31,
	2017			2016			2015
Expected life (in years)	7.3				5.8			6.1
Expected volatility		76.4	%		83.4	%		76.1	%
Expected dividend yield		—	%		—	%		—	%
Risk-free interest rate		1.87	%		1.51	%		1.64	%
Grant date weighted average fair value	$	7.94		$	1.23		$	3.65

The following table summarizes the Company’s share option activity for the year ended December 31, 2017:

	Number of Shares			Weighted- Average Exercise Price		Weighted- Average Remaining Contractual Term (Years)		Aggregate Intrinsic Value (in thousands)
Outstanding – December 31, 2016		413,752		$	2.15
Granted		91,562		$	1.02
Acquired in conjunction with merger with Alcobra Ltd.		418,667		$	26.37
Exercised		(378,343	)	$	2.61			$	504
Forfeited/cancelled		(201,583	)	$	39.90
Outstanding – December 31, 2017		344,055		$	8.70		6.1	$	1,181
Exercisable – December 31, 2017		268,888		$	3.25		5.4	$	709
Exercisable and expected to vest – December 31, 2017		344,055		$	8.70		6.1	$	1,181

At December 31, 2017, the total unrecognized compensation cost of $217,000 will be recognized over the weighted-average remaining service period of approximately 2.8 years. The fair value of the options vested during the years ended December 31, 2017, 2016 and 2015 was $669,000, $171,000 and $177,000, respectively.

During 2017, the Company granted options for 58,600 shares to two board of directors members at an exercise price below fair value at the grant date. The awards were subject to performance conditions based on closing the reverse merger with Alcobra Ltd. and execution of a facility lease. All of the options vested during 2017, and related expense of $568,000 is included in general and administrative expense for the year ended December 31, 2017 related to the awards. There were no options granted that were subject to performance conditions for the years ended December 31, 2016 and 2015.

Options granted that were exercised prior to vesting are subject to repurchase by the Company at the lower of the original issue price or fair value and will vest according to the respective option agreement. A portion of the Company’s share options have been exercised prior to vesting and are not outstanding. As of December 31, 2017, exercisable and expected to vest included 35,595 options which were still subject to future vesting (and which may be repurchased by the Company in the event the option holder ceases to provide services to the Company).

Share-based compensation expenses included in the Company’s statements of operations and comprehensive loss for the years ended December 31, 2017, 2016 and 2015 were:

	For the Year Ended December 31,
(in thousands)	2017		2016		2015
Research and development	$	38	$	217	$	62
General and administrative		2,132		83		37
Total	$	2,170	$	300	$	99

Stock-based compensation expense for the year ended December 31, 2017 includes $1,495,000 of expense related to a modification of a restricted Ordinary Shares agreement as discussed in Note 10.

Income Taxes

12 Months Ended

Dec. 31, 2017

Income Tax Disclosure [Abstract]

Income Taxes

NOTE 12. Income Taxes

A reconciliation of income (loss) before income taxes for domestic and foreign locations for the years ended December 31, 2017, 2016 and 2015 is as follows:

	For the Year Ended December 31,
(In thousands)	2017			2016			2015
United States	$	(10,820	)	$	(1,536	)	$	(1,901	)
Foreign		(81	)		-			-
Total current tax expense	$	(10,901	)	$	(1,536	)	$	(1,901	)

The company accounts for income taxes in accordance with ASC 740-10, Accounting for Uncertainty in Income Taxes. The impact of an uncertain income tax position on the income tax return must be recognized at the largest amount that is more likely than not to be sustained upon audit by the relevant taxing authority. An uncertain tax position will not be recognized if it has less than 50% likelihood of being sustained.

The following table summarizes our gross unrecognized tax benefits (in millions):

	December 31,
	2017		2016		2015
Beginning balance of unrecognized tax benefits	$	0.4	$	0.4	$	0.4
Settlement of prior period tax positions		—		—		—
Increase for prior period tax positions		—		—		—
Increase for current period tax positions		—		—		—
Ending balance of unrecognized tax benefits	$	0.4	$	0.4	$	0.4

Included in the balance of unrecognized tax benefits at December 31, 2017, 2016 and 2015 is $0.4 million, $0.4 million and $0.4 million respectively that could impact our effective tax rate, if recognized. None of the unrecognized tax benefits currently impact our effective tax rate due to the full valuation allowance we have recorded against our deferred tax assets.

The company is subject to taxation and files income tax returns in the United States, California and Israel. Currently, no historical years are under examination. The Company's tax years from 2013 to date are subject to examination by the Israeli, U.S. and state taxing authorities due to the carryforward of unutilized net operating losses and research and development credits. The Company's policy is to recognize interest expense and penalties related to income tax matters as income tax expense. As of December 31, 2017, there are unrecognized tax benefits of $0.2 million and $0.2 million for the United States and California. There was no tax related interest or penalties recognized for the years ended December 31, 2017, 2016 or 2015.

We do not anticipate any material changes to our unrecognized tax benefits within the next twelve months.

The significant components of deferred income taxes at December 31, 2017, 2016 and 2015 are as follows:

	December 31,
(in thousands)	2017			2016			2015
Deferred tax assets:
Net operating loss ⁽¹⁾	$	25,101		$	1,752		$	3,774
Tax credits		35			30			6
Accrued liabilities		227			187			98
Deferred revenue		1,162			2,430			—
Depreciation and amortization		—			—			106
Share-based compensation		90			221			100
Total gross deferred tax assets		26,615			4,620			4,084
Deferred tax liabilities:
Depreciation and amortization		(96	)		(15	)		—
Valuation allowance		(26,519	)		(4,605	)		(4,084	)
Net deferred tax asset	$	—		$	—		$	—

(1)

Included in the deferred tax assets for net operating losses are pre-acquisition Alcobra, Inc. and Alcobra Ltd. federal, state and foreign losses of $0.2 million, $0.1 million and $20.8 million respectively, that the Company is uncertain that the net operating losses will be available for use in the future.

The Company has established a valuation allowance against net deferred tax assets due to the uncertainty that such assets will be realized. Due primarily to the acquisition of Alcobra Ltd. net operating losses, the valuation allowance has increased by $21.9 million between December 31, 2016 and December 31, 2017. The Company periodically evaluates the recoverability of the deferred tax assets. At such time as it is determined that it is more likely than not that deferred tax assets will be realizable, the valuation allowance will be reduced.

At December 31, 2017, the Company had federal and state net operating losses, or NOL, carryforwards of approximately $15.6 million and $15.4 million, respectively. The federal NOL carryforwards begin to expire in 2034, and the state NOL carryforwards begin to expire in 2034. The Company has foreign NOL carryforwards of approximately $90.2 million that do not expire and can be carried forward indefinitely.

At December 31, 2017, the Company had federal and state research and development credit carryforwards of approximately $0.2 million and $0.2 million, respectively. The federal credit carryforwards begin to expire in 2033, and the state credits carry forward indefinitely.

The Company has also incurred research and development expenses of $15.9 million and $17.9 million for the years ended December 31, 2017 and 2016, respectively. The Company believes that a portion of these expenditures will yield additional federal and California tax credits; however, the potential credits under the tax laws have not yet been calculated.

Pursuant to Internal Revenue Code of 1986, as amended (the Code) Sections 382 and 383, annual use of the Company’s federal and California net operating loss and research and development credit carryforwards may be limited in the event a cumulative change in ownership of more than 50% occurs within a three-year period. The Company has not completed a Code Section 382 analysis regarding the limitation of net operating loss carryforwards and other tax attributes. There is a risk that changes in ownership have occurred since Company's formation. If a change in ownership were to have occurred, the NOL carryforwards and other tax attributes could be limited or restricted. If limited, the related asset would be removed from the deferred tax asset schedule with a corresponding reduction in the valuation allowance. Due to the existence of the valuation allowance, limitations created by future ownership changes, if any, related to the Company’s operations in the U.S. will not impact the Company’s effective tax rate.

A reconciliation of the federal statutory income tax rate to the Company’s effective income tax rate is as follows:

	For the Year Ended December 31,
	2017			2016			2015
Federal statutory income tax rate		34.0	%		34.0	%		34.0	%
State income taxes, net of federal benefit		4.4	%		3.1	%		5.0	%
Tax credits		—	%		1.5	%		—	%
Tax Cuts and JOBS Act		(22.0	%)		—	%		—	%
Change in tax rate		(8.3	%)		—	%		—	%
Change in valuation allowance		1.8	%		(33.8	%)		(34.4	%)
Other		(1.6	%)		—	%		—	%
Permanent differences		(8.3	%)		(7.1	%)		(4.6	%)
Provision for income taxes		—	%		(2.3	%)		—	%

On December 22, 2017, the President of the United States signed into law the Tax Cuts and Jobs Act (the "Act"). The Act amends the Internal Revenue Code to reduce tax rates and modify policies, credits, and deductions for individuals and businesses. For businesses, the Act reduces the corporate tax rate from a maximum of 35% to a flat 21% rate. The rate reduction is effective on January 1, 2018. As a result of the rate reduction, the company has reduced the deferred tax asset balance as of December 31, 2017 by $2.4 million. Due to the company's full valuation allowance position, the company has also reduced the valuation allowance by the same amount.

On December 22, 2017, Staff Accounting Bulletin No. 118 ("SAB 118") was issued to address the application of US GAAP in situations when a registrant does not have the necessary information available, prepared, or analyzed (including computations) in reasonable detail to complete the accounting for certain income tax effects of the Act. In accordance with SAB 118, the Company has recognized the provisional tax impacts of the revaluation of the deferred tax assets and liabilities as of December 31, 2017. There was no deferred tax benefit of expense with respect to the remeasurement of certain deferred tax assets and liabilities due to the full valuation allowance against net deferred tax assets. Additional analysis of the law and the impact to the company will be performed and any impact will be recorded in the respective quarter in 2018.

Commitments and Contingencies

12 Months Ended

Dec. 31, 2017

Commitments And Contingencies Disclosure [Abstract]

Commitments and Contingencies

NOTE 13. Commitments and Contingencies

CFFT Funding agreement

The Company has received royalty bearing grants sponsored by CFFT. Should the awards result in a successful product, the Company will pay CFFT a specified payment amount in installments following commercialization based on a formula that is six times the total award amount, plus a payment equal to the awarded payments, within sixty days after aggregate net sales of the product exceed certain thresholds. Further, in the event of a license, sale or other transfer of the product or the Company’s development program technology (including a change of control transaction), the Company will pay CFFT a percentage of such transfer payments actually received by the Company or the Company’s shareholders (subject to a royalty cap). As of December 31, 2017, the Company has received $0.5 million in grants and has not had a successful product utilizing CFFT grants.

Operating Leases

The Company leases approximately 10,335 square feet of office and lab space for its corporate headquarters in San Diego, California under a non-cancelable operating lease. The lease term was from November 2014 to February 2018 and included an option to extend for one additional term of three years. Monthly rental payments were due under the lease and there were escalating rent payments during the term of the lease. In October 2017, the lease was amended in conjunction with the lease of an adjacent office space and extended the lease through five days after the date of occupancy of the adjacent office space, which occurred in March 2018.

In October 2017, the Company entered into a new lease for approximately 24,705 square feet in office space adjacent to its previously occupied headquarters, whose terms provide that the lease will begin on the “Commencement Date” commensurate with delivery of the premises by the landlord (which occurred in March 2018) and will extend for approximately 84 months from the commencement date. Monthly rental payments are due under the lease and there are escalating rent payments during the term of the lease. The Company is also responsible for its proportional share of operating expenses of the building and common areas. In conjunction with the new lease, the Company will receive free rent for four months and received a tenant improvement allowance of $74,000. The lease may be extended for one five year period at then current market rate with annual escalations. The Company entered into an irrevocable standby letter of credit with the landlord for the security deposit of $96,000 upon executing the lease which is included (along with additional funds required to secure the letter of credit) in the balance of other assets as of December 31, 2017.

The Company also leases office space in Pennsylvania under a non-cancelable operating lease which expires in October 2018. This space was subleased beginning in October 2017 through the remaining term of the lease. Sublease income was immaterial for the year ended December 31, 2017, and there was no sublease income in 2016 or 2015.

For operating leases, minimum lease payments, including minimum scheduled rent increases, are recognized as rent expense on a straight-line basis over the lease term. Leasehold improvement incentives paid to the Company by the landlord are recorded as a deferred rent and amortized as a reduction of rent expense over the lease term. Rent expense totaled $334,000, $330,000 and $330,000 for the years ended December 31, 2017, 2016 and 2015, respectively.

Future minimum payments under leases and lease commitments with initial terms greater than one year were as follows at December 31, 2017 (in thousands):

2018	$	556
2019		1,234
2020		1,271
2021		1,310
2022		1,349
Thereafter		3,138
Total	$	8,858

The Company has purchase commitments of $1.5 million related to non-cancellable purchase orders at December 31, 2017.

Related Party Transactions	12 Months Ended
Related Party Transactions	Dec. 31, 2017
Related Party Transactions [Abstract]
Related Party Transactions	Note 14. Related Party Transactions During 2016, the Company entered into a Research Collaboration and License Agreement with a related party, Providence Therapeutics, Inc. (“Providence”) whose CEO and President is also a stockholder of the Company, to identify and optimize microRNA modulators and/or mimetics for the treatment of neoplastic diseases. In April 2017, the Providence Agreement was amended to include mRNA for the treatment of neoplastic disease. As part of the agreement, the Company granted Providence the exclusive rights to research, develop, manufacture and commercialize such products and Providence made an upfront payment of $500,000 which is being amortized over the research term. Each party is responsible for their own research costs under the agreement, and Providence is responsible for all of the development costs through the completion of Phase 2 clinical trials. The Company is entitled to share in future product revenue of each product provided the Company shares in the product’s post Phase 2 costs. Separately, Providence has agreed to pay a specified rate for the use of the Company’s employees. For the years ended December 31, 2017 and 2016, the Company has recognized $1.0 million and $0.5 million, respectively, in revenue related to the amortization of the upfront payment and revenue related to the use of Company employees and expense reimbursements. There were no outstanding accounts receivable related to this agreement as of December 31, 2017 and 2016. During 2017, the Company stock agreement for the President and CEO of Providence was modified to remove the vesting conditions of the original grant and the Company recognized $1.5 million in related stock compensation expense. As of December 31, 2017 and 2016, the President and CEO of Providence held a 5.7% and 10% ownership interest in the Company.

Litigation	12 Months Ended
Litigation	Dec. 31, 2017
Loss Contingency Information About Litigation Matters [Abstract]
Litigation	Note 15. Litigation Israel Litigation On or about February 25, 2018, Joseph Payne, a current Director and former CEO of the Company, filed an action in the District Court at Tel Aviv – Yafo against the Company, its board of directors, Dr. Chivukula, and certain officers alleging that the separation agreement the Company entered into with a resigning officer, Dr. Chivukula, was unlawful and void, and seeking a restraining order and temporary remedies against the Company. Later that same day, in response to the plaintiff’s ex parte request, the court issued a temporary restraining order, ordering the Company to preserve the status quo until the court could consider the matter further. On March 1, 2018, the Company filed a request for clarification of and partial relief from this order. On March 5, 2018, the court ruled on the Company’s request, clarifying its temporary restraining order was limited to the remedies sought in the February 25, 2018 motion. On March 12, 2018, the Company filed an opposition to plaintiff's motion for a restraining order. On March 28, 2018, plaintiff filed a motion seeking to extend the temporary restraining order and asking for various remedies related to a then-scheduled May 7, 2018 Extraordinary General Meeting of the Company’s shareholders that the Company noticed on March 11, 2018, including remedies that might affect the agenda of the Extraordinary General Meeting and therefore the language of the proxy, and seeking to restrain certain conduct, including any changes in the Company's share capital, until such Extraordinary General Meeting. The court ordered the Company to file its answer to this motion by April 15, 2018. On April 8, 2018, the Company filed a notice with the court informing it that, inter alia, due to the fact that Mr. Payne chose to delay his submission of the motion to “expand” the temporary remedies and to question the agenda of the Extraordinary General Meeting – on Friday, April 6, 2018, the Company's Board convened and approved the postponement of the date of the Extraordinary General Meeting, until the court issues a decision on Mr. Payne's motion to 'expand' the temporary remedies. Later that day (April 8, 2018), Mr. Payne moved for another temporary restraining order seeking to prevent the board from delaying the Extraordinary General Meeting. The Company responded to the motion to extend the temporary restraining on April 15, 2018. On May 13, 2018, the court issued its ruling in the motion to expand the temporary remedies. The court set the agenda of the Extraordinary General Meeting, and ordered the Company to convene a Board meeting within seven days, and to summon an Extraordinary General Meeting within 35 days from that date. In addition, the court ruled that the motion regarding the changes in the Company's share capital will be decided in a hearing scheduled for May 23, 2018. On April 18, 2018, the Company sent notice of a board meeting scheduled for April 20, 2018 to approve a private placement transaction. On April 20, 2018, Mr. Payne obtained a temporary restraining order stating that any such approval by the board may be vacated by the court. On April 22, 2018, the Company filed an opposition to the temporary restraining order, on April 25, 2018 the court held an emergency hearing on the temporary restraining order. On April 26, 2018 Mr. Payne and Dr. Chivukula filed a reply to the Company's opposition, and on April 27, 2018 certain other shareholders filed position statements with the court supporting Mr. Payne. On April 27, 2018, the Company filed a notice. On April 29, 2018, the court ruled that the temporary restraining order would stay in place. On May 2, 2018, the Company submitted a motion to amend the protocol of the hearing that took place on April 25, 2018 and to reconsider the decision of April 29, 2018. The Company therefore asked the court to direct that cross- examinations will be held on the hearing scheduled for May 9, 2018, and afterwards the court will reconsider the decision of April 29, 2018. The court ordered Mr. Payne to answer the Company's motions from May 2, 2018 by May 6, 2018. On May 6, 2018, the court ordered the Company to respond to Mr. Payne’s answer to the Company's motions from May 2, 2018 by May 8, 2018. Because of the proximity to the day set for hearing, the Company asked the court to schedule another hearing for the cross- examinations. On May 13, 2018, the court denied the Company's motion to amend the protocol of the hearing that took place on April 25, 2018, but granted the Company's motion to reconsider the decision of April 29, 2018 and ordered that cross- examinations will be held on May 23, 2018. Chivukula Arbitration On March 21, 2018, the Company filed an arbitration demand before JAMS in San Diego, CA, seeking to arbitrate the validity of the separation agreement and related claims between the Company and Dr. Chivukula. On or about April 10, 2018, Dr. Chivukula filed an objection to the arbitration. On or about April 12, 2018, the Company responded to his objection. On April 20, 2018 JAMS preliminarily rejected the basis for Dr. Chivukula’s objection to the arbitration and appointed Mr. Charles H. Dick, Jr. as the arbitrator. No arbitration date has been scheduled. California State Court Litigation On March 27, 2018, the Company and Arcturus Therapeutics, Inc. filed an action in the Superior Court of the State of California, San Diego County captioned Arcturus Therapeutics Ltd.; Arcturus Therapeutics, Inc. v. Joseph E. Payne, Case No. 37-2018-00015271-CU-BC-CTL alleging that Mr. Payne (1) breached his confidentiality and employment agreements, (2) breached his fiduciary duties to the plaintiffs during his service as President and CEO of the plaintiffs and as a director of the plaintiffs’ respective boards of directors, (3) interfered with contractual relations by encouraging Dr. Chivukula, a resigning officer, to breach the consulting agreement entered into by and between Dr. Chivukula and Arcturus Therapeutics, Inc. and the voting trust agreement entered into by and between Dr. Chivukula and the Company, and (4) interfered with prospective business advantage by encouraging Company shareholders to vote against the ratification of the appointment of Ernst & Young LLP in the United States as the Company’s independent auditor. The lawsuit seeks injunctive and monetary relief. Discovery requests have been served on Mr. Payne. The deadline for Mr. Payne to respond to the complaint and the discovery requests is May 15, 2018. A civil case management conference has been set for August 31, 2018. California Federal Court Litigation On April 19, 2018, the Company filed an action in the United States District Court, Southern District of California captioned Arcturus Therapeutics, Inc. v. Joseph E. Payne; Peter Farrell; Andrew Sassine; Bradley Sorenson; James Barlow; and Does 1 through 100, Case No. 18cv766-MMA(NLS) alleging that the Defendants have violated and continue to violate Section 13(d) of the Exchange Act, 15 U.S.C. §78m(d), and Regulation 13D by failing to disclose in Schedule 13D filings the existence of group agreements to buy, sell, or vote shares of the Company and effect a change in the composition of the Company’s board of directors. The lawsuit seeks injunctive relief. On April 24, 2018, the Company filed a motion seeking a Temporary Restraining Order, Preliminary Injunction, and Expedited Discovery. On April 25, 2018, the court denied the Company’s request for a Temporary Restraining Order but scheduled a hearing for the Company’s motion for a Preliminary Injunction and Expedited Discovery for May 21, 2018.

- Definition

Tabular disclosure of the loss contingencies that were reported in the period or disclosed as of the balance sheet date.

+ References

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+ Details

Subsequent Events	12 Months Ended
Subsequent Events	Dec. 31, 2017
Subsequent Events [Abstract]
Subsequent Events	Note 16. Subsequent Events In preparing the financial statements as of December 31, 2016 and for the year then ended, the Company has evaluated subsequent events for recognition and measurement purposes through June 26, 2017, the date the independent auditors' report was originally issued and the audited annual financial statements were available for issuance. After the original issuance of the financial statements and through May 14, 2018, the Company has evaluated subsequent events or transactions that have occurred that may require disclosure in the accompanying financial statements. The Company has concluded that no events or transactions have occurred subsequent to December 31, 2016 that require disclosure. In January 2018, the Company entered into a collaboration agreement with CureVac AG, to jointly discover, develop and commercialize mRNA therapeutics. In February 2018, the Company appointed Mark Herbert as Interim President upon the termination of Joseph E. Payne as President and Chief Executive Officer (See Note 15 Litigation). Additionally, the Company appointed Dr. Christine Esau as Vice President of Research and Development, while announcing the stepping down of Dr. Chivukula as Chief Scientific Officer and Chief Operating Officer and will serve as a Scientific Advisor of the Company. In connection with Dr. Chivukula’s resignation, the Company entered into an agreement providing for cash payment of $335,000 and accelerated vesting of 183,137 Ordinary Shares. The agreement also provided for an additional $100,000 payment to be made for scientific advisory services to be provided for a period of six months following the separation date.

Summary of Significant Accounting Policies (Policies)

12 Months Ended

Dec. 31, 2017

Accounting Policies [Abstract]

Basis of Presentation and Principles of Consolidation

Segment Information

Reclassification of Prior Year's Presentation

Reclassification of Prior Year’s Presentation

Certain prior year amounts have been reclassified for consistency with the current period presentation. This reclassification had no effect on the reported results of operations.

Foreign Currency Translation

Cash and Cash Equivalents

Cash equivalents are short-term highly liquid investments that are readily convertible to cash with original maturities of three months or less at the date of purchase to be cash equivalents.

Restricted Cash

Restricted cash

Statement of cash flows

	As of December 31,
(in thousands)	2017		2016		2015
Cash and cash equivalents	$	24,965	$	8,345	$	11,894
Restricted cash		166		-		-
Restricted cash (included in other assets)		107		-		-
Total cash, cash equivalents and restricted cash shown in the statement of cash flows	$	25,238	$	8,345	$	11,894

Short-term Bank Deposits

Short-term Investments

Fair Value Measurements

Accounts Receivable

Concentration of Credit Risk and Significant Customers

Intangible asset held for sale

Property and Equipment, net

Comprehensive Loss

Revenue Recognition

Research and Development Costs, net

Royalty Bearing Grant

Share-Based Compensation

Ordinary Shares Valuation

Range of Multiple Observed: Using the total deal consideration and the total capital raised prior to the acquisition, the Company estimated the total deal consideration/capital raised multiple;

In making the final determination, the Company determined a discount for lack of marketability.

Income Tax Expense

Net Loss per Share

Recently Issued Accounting Pronouncements

Recently Adopted Accounting Pronouncements

Summary of Significant Accounting Policies (Tables)

12 Months Ended

Dec. 31, 2017

Accounting Policies [Abstract]

Schedule of Cash and Cash Equivalents and Restricted Cash

	As of December 31,
(in thousands)	2017		2016		2015
Cash and cash equivalents	$	24,965	$	8,345	$	11,894
Restricted cash		166		-		-
Restricted cash (included in other assets)		107		-		-
Total cash, cash equivalents and restricted cash shown in the statement of cash flows	$	25,238	$	8,345	$	11,894

Strategic Alliances and Collaboration Agreements (Tables)

12 Months Ended

Dec. 31, 2017

Collaboration Agreements [Abstract]

Summary of Revenues Under Strategic Alliances and Collaborations

The following table summarizes our revenues under strategic alliances and collaborations for the periods indicated (in thousands):

	Year Ended December 31,
(Dollars in thousands)	2017		2016		2015
Collaboration Partner A	$	4,862	$	12,008	$	5,123
Collaboration Partner B		5,639		7,395		979
Collaboration Partner C		1,403		28		-
Other		1,094		951		36
Total	$	12,998	$	20,382	$	6,138

Short-term Investments (Tables)

12 Months Ended

Dec. 31, 2017

Investments Debt And Equity Securities [Abstract]

Summary of Short-term Investments

The following is a summary of short-term investments at December 31, 2017:

	December 31, 2017
(Dollars in thousands)	Amortized cost		Gross unrealized gains		Gross unrealized losses			Fair value
Certificates of deposit	$	1,462	$	-	$	-		$	1,462
Corporate debt securities		7,149		-		(3	)		7,146
Total	$	8,611	$	-	$	(3	)	$	8,608

- Definition

Tabular disclosure of available-for-sale securities which includes, but is not limited to, changes in the cost basis and fair value, fair value and gross unrealized gain (loss), fair values by type of security, contractual maturity and classification, amortized cost basis, contracts to acquire securities to be accounted for as available-for-sale, debt maturities, transfers to trading, change in net unrealized holding gain (loss) net of tax, continuous unrealized loss position fair value, aggregate losses qualitative disclosures, other than temporary impairment (OTTI) losses or other disclosures related to available for sale securities.

+ References + Details

Fair Value Measurements (Tables)

12 Months Ended

Dec. 31, 2017

Fair Value Disclosures [Abstract]

Schedule of Financial Assets Measured at Fair Value on a Recurring Basis

The following table presents our fair value hierarchy for assets measured at fair value on a recurring basis as of December 31, 2017 (in thousands):

	December 31, 2017
	Fair value measurements using input type
	Level 1		Level 2		Level 3		Total
Cash equivalents	$	2,024	$	-	$	-	$	2,024
Certificates of deposit		-		1,462		-		1,462
Corporate debt securities		-		7,146		-		7,146
Total financial assets	$	2,024	$	8,608	$	-	$	10,632

- Definition

Tabular disclosure of financial instruments measured at fair value, including those classified in shareholders' equity measured on a recurring or nonrecurring basis. Disclosures include, but are not limited to, fair value measurements recorded and the reasons for the measurements, level within the fair value hierarchy in which the fair value measurements are categorized and transfers between levels 1 and 2. Nonrecurring fair value measurements are those that are required or permitted in the statement of financial position in particular circumstances.

+ References + Details

Reverse Merger with Alcobra Ltd. (Tables)

12 Months Ended

Dec. 31, 2017

Business Combinations [Abstract]

Summary of Fair Value of Assets and Liabilities Acquired

The following summarizes the estimated fair value of the assets and liabilities acquired at the date of the merger:


(in thousands)
Cash and cash equivalents	$	2,032
Restricted cash		179
Short-term investments		34,188
Prepaid and other assets		434
Property, plant and equipment – held for sale		29
Intangible asset-held for sale		590
Total assets acquired		37,452
Accounts payable and accrued expenses		(1,906	)
Net assets acquired	$	35,546

Balance Sheet Details (Tables)

12 Months Ended

Dec. 31, 2017

Balance Sheet Related Disclosures [Abstract]

Schedule of Prepaid Expenses and Other Current Assets

Prepaid expenses and other current assets consisted of the following as of December 31, 2017 and December 31, 2016:

	December 31,
(in thousands)	2017		2016
Prepaid expenses	$	704	$	242
Other current assets		355		111
Total	$	1,059	$	353

Schedule of Accrued Liabilities

Accrued liabilities consisted of the following as of December 31, 2017 and December 31, 2016:

	December 31,
(in thousands)	2017		2016
Accrued compensation	$	1,812	$	369
Other accrued liabilities		981		692
Total	$	2,793	$	1,061

Property and Equipment, Net (Tables)

12 Months Ended

Dec. 31, 2017

Property Plant And Equipment [Abstract]

Summary of Components of Property and Equipment

Property and equipment, net consisted of the following:

	December 31,
(in thousands)	2017			2016
Research equipment	$	1,620		$	1,495
Computers and software		97			98
Office equipment and furniture		255			255
Leasehold improvements		44			44
Total		2,016			1,892
Less accumulated depreciation and amortization		(967	)		(557	)
Property and equipment, net	$	1,049		$	1,335

Share-Based Compensation (Tables)

12 Months Ended

Dec. 31, 2017

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Schedule of Weighted Average Assumptions Used in Black -Scholes Valuation Model

The following table presents the weighted-average assumptions used in the Black-Scholes valuation model by the Company in calculating the fair value of share options granted:

	For the Year Ended December 31,
	2017			2016			2015
Expected life (in years)	7.3				5.8			6.1
Expected volatility		76.4	%		83.4	%		76.1	%
Expected dividend yield		—	%		—	%		—	%
Risk-free interest rate		1.87	%		1.51	%		1.64	%
Grant date weighted average fair value	$	7.94		$	1.23		$	3.65

Summary of Share Option Activity

The following table summarizes the Company’s share option activity for the year ended December 31, 2017:

	Number of Shares			Weighted- Average Exercise Price		Weighted- Average Remaining Contractual Term (Years)		Aggregate Intrinsic Value (in thousands)
Outstanding – December 31, 2016		413,752		$	2.15
Granted		91,562		$	1.02
Acquired in conjunction with merger with Alcobra Ltd.		418,667		$	26.37
Exercised		(378,343	)	$	2.61			$	504
Forfeited/cancelled		(201,583	)	$	39.90
Outstanding – December 31, 2017		344,055		$	8.70		6.1	$	1,181
Exercisable – December 31, 2017		268,888		$	3.25		5.4	$	709
Exercisable and expected to vest – December 31, 2017		344,055		$	8.70		6.1	$	1,181

Schedule of Share-based Compensation Expenses

Share-based compensation expenses included in the Company’s statements of operations and comprehensive loss for the years ended December 31, 2017, 2016 and 2015 were:

	For the Year Ended December 31,
(in thousands)	2017		2016		2015
Research and development	$	38	$	217	$	62
General and administrative		2,132		83		37
Total	$	2,170	$	300	$	99

Income Taxes (Tables)

12 Months Ended

Dec. 31, 2017

Income Tax Disclosure [Abstract]

Summary of Reconciliation of Income (Loss) Before Income Taxes for Domestic and Foreign Locations

A reconciliation of income (loss) before income taxes for domestic and foreign locations for the years ended December 31, 2017, 2016 and 2015 is as follows:

	For the Year Ended December 31,
(In thousands)	2017			2016			2015
United States	$	(10,820	)	$	(1,536	)	$	(1,901	)
Foreign		(81	)		-			-
Total current tax expense	$	(10,901	)	$	(1,536	)	$	(1,901	)

Summary of Gross Unrecognized Tax Benefits

The following table summarizes our gross unrecognized tax benefits (in millions):

	December 31,
	2017		2016		2015
Beginning balance of unrecognized tax benefits	$	0.4	$	0.4	$	0.4
Settlement of prior period tax positions		—		—		—
Increase for prior period tax positions		—		—		—
Increase for current period tax positions		—		—		—
Ending balance of unrecognized tax benefits	$	0.4	$	0.4	$	0.4

Significant Components of Deferred Income Taxes

The significant components of deferred income taxes at December 31, 2017, 2016 and 2015 are as follows:

	December 31,
(in thousands)	2017			2016			2015
Deferred tax assets:
Net operating loss ⁽¹⁾	$	25,101		$	1,752		$	3,774
Tax credits		35			30			6
Accrued liabilities		227			187			98
Deferred revenue		1,162			2,430			—
Depreciation and amortization		—			—			106
Share-based compensation		90			221			100
Total gross deferred tax assets		26,615			4,620			4,084
Deferred tax liabilities:
Depreciation and amortization		(96	)		(15	)		—
Valuation allowance		(26,519	)		(4,605	)		(4,084	)
Net deferred tax asset	$	—		$	—		$	—

Reconciliation of Federal Statutory Income Tax Rate to Company's Effective Income Tax Rate

A reconciliation of the federal statutory income tax rate to the Company’s effective income tax rate is as follows:

	For the Year Ended December 31,
	2017			2016			2015
Federal statutory income tax rate		34.0	%		34.0	%		34.0	%
State income taxes, net of federal benefit		4.4	%		3.1	%		5.0	%
Tax credits		—	%		1.5	%		—	%
Tax Cuts and JOBS Act		(22.0	%)		—	%		—	%
Change in tax rate		(8.3	%)		—	%		—	%
Change in valuation allowance		1.8	%		(33.8	%)		(34.4	%)
Other		(1.6	%)		—	%		—	%
Permanent differences		(8.3	%)		(7.1	%)		(4.6	%)
Provision for income taxes		—	%		(2.3	%)		—	%

Commitments and Contingencies (Tables)

12 Months Ended

Dec. 31, 2017

Commitments And Contingencies Disclosure [Abstract]

Schedule of Future Minimum Payments Under Leases and Lease Commitments

Future minimum payments under leases and lease commitments with initial terms greater than one year were as follows at December 31, 2017 (in thousands):

2018	$	556
2019		1,234
2020		1,271
2021		1,310
2022		1,349
Thereafter		3,138
Total	$	8,858

Organization (Details Textual) $ / shares in Units, $ in Thousands	Nov. 15, 2017 ₪ / shares shares	Dec. 31, 2017 USD ($)	Dec. 31, 2017 ₪ / shares	Dec. 31, 2016 USD ($) $ / shares
Organization and Significant Accounting Policies [Line Items]
Business merger date	Nov. 15, 2017
Par value per share \| (per share)			₪ 0.07	$ 0.0001
Reverse split of ordinary shares	1-for-7
Reverse split of ordinary shares, ratio	0.1429
Accumulated deficit		$ (23,089)		$ (12,187)
Cash equivalents and short-term investments acquired		$ 36,400
Alcobra [Member]
Organization and Significant Accounting Policies [Line Items]
Stock issued during period, shares, acquisitions \| shares	6,631,712
Par value per share \| ₪ / shares	₪ 0.07

Summary of Significant Accounting Policies (Details Textual)	12 Months Ended
	Dec. 31, 2017 USD ($) Customer shares	Dec. 31, 2016 USD ($) Customer shares	Dec. 31, 2015 USD ($) Customer shares
Summary Of Significant Accounting Policy [Line Items]
Restricted cash, current	$ 166,000
Restricted cash, non-current	$ 107,000
Lease expiration year	2025
Restricted cash		$ 0
Reserves for accounts receivable	$ 0	0
Impairment losses	0	0	$ 0
Royalty-bearing grants from Cystic Fibrosis Foundation Therapeutics, Inc.	$ 300,000	$ 200,000
Share options expiration period	10 years
Vesting period	4 years
Vesting description	Share options have a ten-year life and generally vest 25% on the first anniversary of the grant and in 1/48th equal installments on each monthly anniversary thereafter, such that options are fully vested on the four-year anniversary of the date of grant.
Antidilutive securities excluded from computation of earnings per share \| shares	3,057,000	2,800,000	3,843,000
Treasury shares \| shares	43,000	0	0
Dividends declared	$ 0	$ 0	$ 0
Dividends paid	$ 0	$ 0	$ 0
Exercise of Share Options and Subject to Future Vesting and Unvested Restricted Stock [Member]
Summary Of Significant Accounting Policy [Line Items]
Antidilutive securities excluded from computation of earnings per share \| shares	702,000	769,000	769,000
First Year Anniversary of the Grant [Member]
Summary Of Significant Accounting Policy [Line Items]
Vesting percentage	25.00%
Collaboration Partner A [Member] \| Research Collaboration and Exclusive License Agreement [Member]
Summary Of Significant Accounting Policy [Line Items]
Deferred revenue	$ 7,600,000	$ 400,000
Collaboration Partner B [Member] \| Research Collaboration and Exclusive License Agreement [Member]
Summary Of Significant Accounting Policy [Line Items]
Deferred revenue	5,800,000	6,200,000
Collaboration Partner C [Member] \| Research Collaboration and Exclusive License Agreement [Member]
Summary Of Significant Accounting Policy [Line Items]
Deferred revenue		200,000
Other Collaboration [Member] \| Research Collaboration and Exclusive License Agreement [Member]
Summary Of Significant Accounting Policy [Line Items]
Deferred revenue	$ 200,000	$ 800,000
Minimum [Member]
Summary Of Significant Accounting Policy [Line Items]
Property and equipment, useful lives	3 years
Multiple applied for estimates	1.00
Maximum [Member]
Summary Of Significant Accounting Policy [Line Items]
Property and equipment, useful lives	5 years
Multiple applied for estimates	1.50
Credit Risk [Member] \| Account Receivable [Member]
Summary Of Significant Accounting Policy [Line Items]
Number of customers \| Customer	1	1
Concentration risk, percentage		88.00%
Credit Risk [Member] \| Revenue [Member]
Summary Of Significant Accounting Policy [Line Items]
Number of customers \| Customer	3	2	2
Concentration risk, percentage	92.00%	95.00%	99.00%

Schedule of Cash and Cash Equivalents and Restricted Cash (Details) - USD ($)	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Accounting Policies [Abstract]
Cash and cash equivalents	$ 24,965,000	$ 8,345,000	$ 11,894,000
Restricted cash	166,000
Restricted cash (included in other assets)	107,000
Total cash, cash equivalents and restricted cash shown in the statement of cash flows	$ 25,238,000	$ 8,345,000	$ 11,894,000	$ 1,922,000

Strategic Alliances and Collaboration Agreements - Summary of Revenues Under Strategic Alliances and Collaborations (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Revenue in conjunction with strategic alliances and collaborations	$ 12,998	$ 20,382	$ 6,138
Research Collaboration and Exclusive License Agreement [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Revenue in conjunction with strategic alliances and collaborations	12,998	20,382	6,138
Research Collaboration and Exclusive License Agreement [Member] \| Collaboration Partner A [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Revenue in conjunction with strategic alliances and collaborations	4,862	12,008	5,123
Research Collaboration and Exclusive License Agreement [Member] \| Collaboration Partner B [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Revenue in conjunction with strategic alliances and collaborations	5,639	7,395	979
Research Collaboration and Exclusive License Agreement [Member] \| Collaboration Partner C [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Revenue in conjunction with strategic alliances and collaborations	1,403	28
Research Collaboration and Exclusive License Agreement [Member] \| Other Collaboration [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Revenue in conjunction with strategic alliances and collaborations	$ 1,094	$ 951	$ 36

Strategic Alliances and Collaboration Agreements (Details Textual) $ in Thousands	12 Months Ended
	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($) Agreement
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Revenue in conjunction with strategic alliances and collaborations	$ 12,998	$ 20,382	$ 6,138
Research Collaboration and Exclusive License Agreement [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Revenue in conjunction with strategic alliances and collaborations	$ 12,998	$ 20,382	$ 6,138
Collaboration Partner A [Member] \| Research Collaboration and Exclusive License Agreement [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Number of collaboration agreements \| Agreement			2
Revenue recognition research activities period			23 months
License additional extension period		42 days
Revenue recognition, milestone	The Company also reached certain milestones in 2015 and in 2016 that were determined, as of the inception of the agreement, to be substantive and the revenue related to these milestones was recognized when they were achieved.
Revenue in conjunction with strategic alliances and collaborations	$ 4,862	$ 12,008	$ 5,123
Labor and expense reimbursements revenue	4,400	9,500	3,000
Revenue recognition potential milestone revenue recognized	56,500
Collaboration Partner A [Member] \| Research Collaboration and Exclusive License Agreement [Member] \| Minimum [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Option exercise revenue range per target	1,000
Collaboration Partner A [Member] \| Research Collaboration and Exclusive License Agreement [Member] \| Maximum [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Option exercise revenue range per target	$ 5,000
Collaboration Partner B [Member] \| Research Collaboration and Exclusive License Agreement [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Revenue recognition, milestone	Collaboration B will pay the Company a one-time milestone payment after the first optimized lead designation for the first product with respect of such development target.
Revenue in conjunction with strategic alliances and collaborations	$ 5,639	7,395	979
Labor and expense reimbursements revenue	3,700	$ 3,800	$ 300
Revenue recognition potential milestone revenue recognized	133,000
Revenue recognized as one time payment	$ 2,000
Collaboration Partner B [Member] \| Research Collaboration and Exclusive License Agreement [Member] \| Maximum [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Royalty payment percentage	10.00%
Collaboration Partner C [Member] \| Research Collaboration and Exclusive License Agreement [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Revenue recognition research activities period		18 months
License additional extension period		18 months
Revenue in conjunction with strategic alliances and collaborations	$ 1,403	$ 28
Upfront fee received		100
Regularly scheduled research funding payments		$ 3,700

Short-term Investments - (Details Textual) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Schedule Of Available For Sale Securities [Line Items]
Short-term bank deposits	$ 23,608
Short Term Deposit Weighted Average Interest Rate	1.60%
Short-term investments		$ 0
Bank Deposits
Schedule Of Available For Sale Securities [Line Items]
Short-term bank deposits	$ 15,000	$ 0

Summary of Short-term Investments (Details) $ in Thousands	Dec. 31, 2017 USD ($)
Schedule Of Available For Sale Securities [Line Items]
Amortized cost	$ 8,611
Gross unrealized gains	0
Gross unrealized losses	(3)
Fair value	8,608
Certificates of Deposit [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized cost	1,462
Gross unrealized gains	0
Gross unrealized losses	0
Fair value	1,462
Corporate Debt Securities [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized cost	7,149
Gross unrealized gains	0
Gross unrealized losses	(3)
Fair value	$ 7,146

Schedule of Financial Assets Measured at Fair Value on a Recurring Basis (Details) - Fair Value, Measurements, Recurring [Member] - USD ($)	Dec. 31, 2017	Dec. 31, 2016
Assets, Fair Value Disclosure [Abstract]
Cash equivalents	$ 2,024,000
Certificates of deposit	1,462,000
Corporate debt securities	7,146,000
Total financial assets	10,632,000	$ 0
Fair Value, Inputs, Level 1 [Member]
Assets, Fair Value Disclosure [Abstract]
Cash equivalents	2,024,000
Total financial assets	2,024,000
Fair Value, Inputs, Level 2 [Member]
Assets, Fair Value Disclosure [Abstract]
Certificates of deposit	1,462,000
Corporate debt securities	7,146,000
Total financial assets	$ 8,608,000

Reverse Merger with Alcobra Ltd. (Details 1) - USD ($) $ in Thousands	Dec. 31, 2017	Nov. 15, 2017
Business Acquisition [Line Items]
Intangible asset held for sale	$ 590
Alcobra [Member]
Business Acquisition [Line Items]
Cash and cash equivalents		$ 2,032
Restricted cash		179
Short-term investments		34,188
Prepaid and other assets		434
Property, plant and equipment – held for sale		29
Intangible asset held for sale		590
Total assets acquired		37,452
Accounts payable and accrued expenses		(1,906)
Net assets acquired		$ 35,546

Reverse Merger with Alcobra Ltd. (Details Textual)	12 Months Ended
Reverse Merger with Alcobra Ltd. (Details Textual)	Dec. 31, 2017 USD ($) $ / shares shares
Amiservice [Member]
Business Acquisition [Line Items]
Equity method investment, description	Assets acquired in the merger included an intangible asset consisting of in-process research and development for proprietary drug technology called ADAIR. At the closing date of the reverse merger, we entered into an agreement with Amiservice to which we agreed to transfer certain intellectual property related to ADAIR in exchange for a minority equity stake in a company to be formed by Amiservice for the purpose of acquiring the ADAIR assets. The agreement is subject to certain closing conditions that have not been met. The Company determined that the asset met the classification criteria as held for sale in accordance with related accounting guidance when acquired and remained held for sale at December 31, 2017
Alcobra [Member]
Business Acquisition [Line Items]
Total fair value of consideration paid	$ 40,841,000
Shares outstanding as on merger date \| shares	3,997,000
Closing price as on merger date \| $ / shares	$ 10.22
Charge to additional paid in capital	$ 5,295,000
Payments for merger related costs	$ 1,734,000

Balance Sheet Details - Schedule of Prepaid Expenses and Other Current Assets (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Prepaid Expenses And Other Current Assets [Abstract]
Prepaid expenses	$ 704	$ 242
Other current assets	355	111
Total	$ 1,059	$ 353

Balance Sheet Details - Schedule of Accrued Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Accrued Liabilities Current [Abstract]
Accrued compensation	$ 1,812	$ 369
Other accrued liabilities	981	692
Total	$ 2,793	$ 1,061

Property and Equipment, Net (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Property Plant And Equipment [Line Items]
Property and equipment, gross	$ 2,016	$ 1,892
Less accumulated depreciation and amortization	(967)	(557)
Property and equipment, net	1,049	1,335
Research equipment [Member]
Property Plant And Equipment [Line Items]
Property and equipment, gross	1,620	1,495
Computer and software [Member]
Property Plant And Equipment [Line Items]
Property and equipment, gross	97	98
Office equipment and furniture [Member]
Property Plant And Equipment [Line Items]
Property and equipment, gross	255	255
Leasehold improvements [Member]
Property Plant And Equipment [Line Items]
Property and equipment, gross	$ 44	$ 44

Convertible Promissory Notes (Details Textual) - USD ($)		12 Months Ended
	Nov. 15, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Aug. 31, 2015
Short Term Debt [Line Items]
Proceeds from convertible debt		$ 5,650,000		$ 1,885,000
Beneficial conversion expense from notes		348,000	$ 250,000
Conversion of notes to Ordinary Shares		5,957,000
Interest expense on convertible promissory notes		$ 150,000	295,000	$ 251,000
Series A Preferred Stock
Short Term Debt [Line Items]
Convertible promissory note, amount converted			$ 6,228,989
Number of shares issued upon the conversion of convertible promissory note			521,449
Second Notes [Member]
Short Term Debt [Line Items]
Convertible promissory note, maturity date				Dec. 31, 2016
Convertible promissory note, interest rate		5.00%
Convertible Promissory Notes [Member]
Short Term Debt [Line Items]
Conversion percentage of capital stock		5.00%			5.00%
Proceeds from convertible debt		$ 5,675,000			$ 5,900,000
Convertible promissory note, maturity date		Feb. 28, 2019
Convertible promissory note, amount converted	$ 5,795,000
Accrued interest	162,000
Beneficial conversion expense from notes	348,000
Repayments of convertible promissory notes			$ 135,000
Convertible promissory notes outstanding amount			120,000
Conversion of notes to Ordinary Shares	$ 616,824
Common stock average conversion rate	$ 10.19
Interest expense on convertible promissory notes		$ 150,000	295,000	$ 251,000
Convertible Promissory Notes [Member] \| Series A Preferred Stock
Short Term Debt [Line Items]
Convertible promissory note, amount converted			5,670,000
Accrued interest			$ 560,000
Number of shares issued upon the conversion of convertible promissory note			521,415
Beneficial conversion expense from notes			$ 250,000

Shareholders' Equity (Details Textual)		1 Months Ended				12 Months Ended
Shareholders' Equity (Details Textual)	Nov. 15, 2017 shares	Jan. 31, 2014 $ / shares shares	Dec. 31, 2013 $ / shares shares	Apr. 30, 2013 $ / shares shares	Mar. 31, 2013 $ / shares shares	Dec. 31, 2017 USD ($) Milestone shares	Dec. 31, 2016 USD ($) Milestone $ / shares shares	Dec. 31, 2015 USD ($)
Class Of Stock [Line Items]
Reverse split of ordinary shares	1-for-7
Reverse split of ordinary shares, ratio	0.1429
Common stock, shares authorized	30,000,000					30,000,000
Share based compensation expense \| $						$ 2,170,000	$ 300,000	$ 99,000
Restricted Common Stock [Member]
Class Of Stock [Line Items]
Stock issued during period					2,783,686
Share price of stock issued \| $ / shares					$ 0.0068
Shares subject to repurchase option					1,538,353
Share based compensation arrangement by share based payment award period from termination date of employee or consultant for repurchase of shares					2 months
Number of milestones achieved \| Milestone						2	2
Common shares, unvested						622,667	769,176
Share based compensation expense \| $						$ 1,495,000
First Year Anniversary of the Grant [Member]
Class Of Stock [Line Items]
Shares vesting percentage						25.00%
First Year Anniversary of the Grant [Member] \| Restricted Common Stock [Member]
Class Of Stock [Line Items]
Shares vesting percentage					25.00%
Vested After in Vivo Proof-of-concept Achieved [Member] \| Restricted Common Stock [Member]
Class Of Stock [Line Items]
Shares vesting percentage					25.00%
Vested After IND Application Completed [Member] \| Restricted Common Stock [Member]
Class Of Stock [Line Items]
Shares vesting percentage					25.00%
Vested After in Human Efficacy Achieved [Member] \| Restricted Common Stock [Member]
Class Of Stock [Line Items]
Shares vesting percentage					25.00%
Warrant
Class Of Stock [Line Items]
Warrant outstanding							192,647
Warrant price per share \| $ / shares							$ 1.02
Common shares issued upon warrant conversion						188,980
Proceeds from warrant exercised \| $						$ 160,000
Arcturus Therapeutics Inc [Member] \| Ordinary Shares [Member]
Class Of Stock [Line Items]
Stock conversion ratio	0.293
Series Seed Preferred Stock [Member]
Class Of Stock [Line Items]
Preferred stock, shares outstanding						0	1,284,000
Series Seed Preferred Stock [Member] \| Private Placement [Member]
Class Of Stock [Line Items]
Stock issued during period				1,284,402
Preferred stock price per share \| $ / shares				$ 1.02
Warrants issued for each share of stock granted the investor				0.15
Purchase shares of common stock at a strike price \| $ / shares				$ 1.02
Maximum maturity term of warrants				10 years
Series A Preferred Stock
Class Of Stock [Line Items]
Convertible promissory note, amount converted \| $							$ 6,228,989
Number of shares issued upon the conversion of convertible promissory note							521,449
Preferred stock, shares outstanding						0	1,481,000
Series A Preferred Stock \| Minimum [Member]
Class Of Stock [Line Items]
Debt conversion converted instrument price per share \| $ / shares							$ 11.60
Series A Preferred Stock \| Maximum [Member]
Class Of Stock [Line Items]
Debt conversion converted instrument price per share \| $ / shares							$ 12.97
Series A Preferred Stock \| Private Placement [Member]
Class Of Stock [Line Items]
Stock issued during period		959,641	959,641
Preferred stock price per share \| $ / shares		$ 5.46	$ 5.46
Series Seed and Series A preferred Stock [Member]
Class Of Stock [Line Items]
Preferred stock, shares outstanding	2,765,492
Preferred stock converted into common stock	2,765,492

Share-Based Compensation (Details Textual)		12 Months Ended
Share-Based Compensation (Details Textual)	Nov. 15, 2017	Dec. 31, 2017 USD ($) Director shares	Dec. 31, 2016 USD ($) shares	Dec. 31, 2015 USD ($) shares
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share options expiration period		10 years
Reverse split of ordinary shares	1-for-7
Reverse split of ordinary shares, ratio	0.1429
Compensation cost not yet recognized \| $		$ 217,000
Weighted-average remaining service period		2 years 9 months 18 days
fairr value of options vested \| $		$ 669,000	$ 171,000	$ 177,000
Number of Shares, Granted		91,562
Share based compensation expense \| $		$ 2,170,000	300,000	99,000
Exercisable and expected to vest options, subject to repuchase conditions		35,595
General and Administrative Expense
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share based compensation expense \| $		$ 2,132,000	$ 83,000	$ 37,000
Stock Options [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of board of directors \| Director		2
Performance Based Options
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of Shares, Granted			0	0
Performance Based Options \| Director [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of Shares, Granted		58,600
Performance Based Options \| General and Administrative Expense
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share based compensation expense \| $		$ 568,000
Restricted Common Stock [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share based compensation expense \| $		$ 1,495,000
2013 Equity Incentive Plan [Member] \| Stock Options [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares authorized for grant		0
Share options expiration period		10 years
Common stock reserved for future issuance		0
2010 Equity Incentive Plan [Member] \| Stock Options [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share options expiration period		10 years
Common stock reserved for future issuance		465,558

Share-Based Compensation (Details) - $ / shares	12 Months Ended
Share-Based Compensation (Details) - $ / shares	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Grant date weighted average fair value	$ 7.94	$ 1.23	$ 3.65
Stock Options [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected life (in years)	7 years 3 months 19 days	5 years 9 months 18 days	6 years 1 month 6 days
Expected volatility	76.40%	83.40%	76.10%
Risk-free interest rate	1.87%	1.51%	1.64%

Share-Based Compensation (Details 1) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2017 USD ($) $ / shares shares
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Number of Shares, Outstanding \| shares	413,752
Number of Shares, Granted \| shares	91,562
Number of Shares, Acquired in conjunction with merger with Alcobra Ltd. \| shares	418,667
Number of Shares, Exercised \| shares	(378,343)
Number of Shares, Forfeited/cancelled \| shares	(201,583)
Number of Shares, Outstanding \| shares	344,055
Number of Shares, Exercisable – December 31, 2017 \| shares	268,888
Number of Shares, Exercisable and expected to vest – December 31, 2017 \| shares	344,055
Weighted-Average Exercise Price, Outstanding \| $ / shares	$ 2.15
Weighted-Average Exercise Price, Granted \| $ / shares	1.02
Weighted-Average Exercise Price, Acquired in conjunction with merger with Alcobra Ltd. \| $ / shares	26.37
Weighted-Average Exercise Price, Exercised \| $ / shares	2.61
Weighted-Average Exercise Price, Forfeited/cancelled \| $ / shares	39.90
Weighted-Average Exercise Price, Outstanding \| $ / shares	8.70
Weighted-Average Exercise Price, Exercisable – December 31, 2017 \| $ / shares	3.25
Weighted-Average Exercise Price, Exercisable and expected to vest – December 31, 2017 \| $ / shares	$ 8.70
Weighted-Average Remaining Contractual Term (Years), Outstanding – December 31, 2017	6 years 1 month 6 days
Weighted-Average Remaining Contractual Term (Years), Exercisable – December 31, 2017	5 years 4 months 24 days
Weighted-Average Remaining Contractual Term (Years), Exercisable and expected to vest – December 31, 2017	6 years 1 month 6 days
Aggregate Intrinsic Value, Exercised \| $	$ 504
Aggregate Intrinsic Value, Outstanding – December 31, 2017 \| $	1,181
Aggregate Intrinsic Value, Exercisable – December 31, 2017 \| $	709
Aggregate Intrinsic Value, Exercisable and expected to vest – December 31, 2017 \| $	$ 1,181

Share-Based Compensation (Details 2) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share-based compensation expenses	$ 2,170	$ 300	$ 99
Research and Development [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share-based compensation expenses	38	217	62
General and Administrative [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share-based compensation expenses	$ 2,132	$ 83	$ 37

Income Taxes (Details 1) - USD ($) $ in Thousands	12 Months Ended
Income Taxes (Details 1) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
United States	$ (10,820)	$ (1,536)	$ (1,901)
Foreign	(81)
Total current tax expense	$ (10,901)	$ (1,536)	$ (1,901)

Income Taxes (Details Textual) - USD ($)		12 Months Ended
Income Taxes (Details Textual) - USD ($)	Jan. 01, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Income Taxes [Line Items]
Maximum percentage of likelihood of uncertain tax position recognized to be sustained		50.00%
Unrecognized tax benefits		$ 400,000	$ 400,000	$ 400,000	$ 400,000
Unrecognized tax benefits impacting effective tax rate		0	0	0
Tax related interest or penalties recognized		0	0	0
Research and Development Expenses		$ 15,918,000	$ 17,934,000	$ 5,476,000
Net Operating Loss and Research and Development Credit Carryforwards Limitations on Cumulative Change In Ownership Minimum Percentage		50.00%
Net Operating Loss and Research and Development Credit Carryforwards Limitations on Cumulative Change In Ownership Period		3 years
Federal statutory income tax rate		34.00%	34.00%	34.00%
Reduction in Deferred Tax Assets		$ 2,400,000
Maximum [Member]
Income Taxes [Line Items]
Federal statutory income tax rate		35.00%
Scenario Plan [Memebr]
Income Taxes [Line Items]
Federal statutory income tax rate	21.00%
Federal [Member]
Income Taxes [Line Items]
Net Operating Loss Carryforwards		$ 15,600,000
Operating Loss Carryforwards Expiration Year		2034
Federal [Member] \| Research and Development [Member]
Income Taxes [Line Items]
Credit Carryforward Amount		$ 200,000
Credit Carryforward Expiration Year		2033
State [Member]
Income Taxes [Line Items]
Net Operating Loss Carryforwards		$ 15,400,000
Operating Loss Carryforwards Expiration Year		2034
State [Member] \| Research and Development [Member]
Income Taxes [Line Items]
Credit Carryforward Amount		$ 200,000
Foreign [Member]
Income Taxes [Line Items]
Net Operating Loss Carryforwards		90,200,000
Alcobra [Member]
Income Taxes [Line Items]
Increase in valuation allowance, net operating losses		21,900,000
United States
Income Taxes [Line Items]
Unrecognized tax benefits		200,000
California
Income Taxes [Line Items]
Unrecognized tax benefits		$ 200,000

Income Taxes (Details 3 ) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Deferred tax assets:
Net operating loss (1)	$ 25,101	$ 1,752	$ 3,774
Tax credits	35	30	6
Accrued liabilities	227	187	98
Deferred revenue	1,162	2,430	0
Depreciation and amortization		0	106
Share-based compensation	90	221	100
Total gross deferred tax assets	26,615	4,620	4,084
Deferred tax liabilities:
Depreciation and amortization	(96)	(15)
Valuation allowance	(26,519)	(4,605)	(4,084)
Net deferred tax asset	$ 0	$ 0	$ 0

Income Taxes (Details 3 ) (Parenthetical) $ in Millions	Dec. 31, 2017 USD ($)
Income Tax Disclosure [Abstract]
Deferred tax assets pre acquisition, federal	$ 0.2
Deferred tax assets pre acquisition, state	0.1
Deferred tax assets pre acquisition, foreign	$ 20.8

Income Taxes (Details 4)	12 Months Ended
Income Taxes (Details 4)	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Federal statutory income tax rate	34.00%	34.00%	34.00%
State income taxes, net of federal benefit	4.40%	3.10%	5.00%
Tax credits	(0.00%)	1.50%	(0.00%)
Tax Cuts and JOBS Act	(22.00%)	0.00%	0.00%
Change in tax rate	(8.30%)	0.00%	0.00%
Change in valuation allowance	1.80%	(33.80%)	(34.40%)
Other	(1.60%)	0.00%	0.00%
Permanent differences	(8.30%)	(7.10%)	(4.60%)
Provision for income taxes	0.00%	(2.30%)	0.00%

Commitments and Contingencies (Details Textual)	1 Months Ended		12 Months Ended
Commitments and Contingencies (Details Textual)	Mar. 31, 2018	Oct. 31, 2017 USD ($) ft²	Dec. 31, 2017 USD ($) ft²	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Commitment And Contingencies [Line Items]
Operating lease expiration period year and month			Oct. 31, 2018
Sublease income				$ 0	$ 0
Operating lease rent expense			$ 334,000	$ 330,000	$ 330,000
Purchase commitments related to non-cancellable purchase orders			$ 1,500,000
October 2017 Lease Amendment [Member]
Commitment And Contingencies [Line Items]
Operating lease extended additional term		84 months
Lessor, operating lease, term of contract		4 months
Tenant improvement allowance		$ 74,000
Lessor leasing arrangements operating leases extended lease		15 years
Security deposit		$ 96,000
Property Subject to Operating Lease [Member] \| October 2017 Lease Amendment [Member]
Commitment And Contingencies [Line Items]
Leased area \| ft²		24,705
San Diego, California [Member]
Commitment And Contingencies [Line Items]
Leased area \| ft²			10,335
Operating lease initial period year and month			2014-11
Operating lease expiration period year and month			2018-02
Operating lease extended additional term			3 years
San Diego, California [Member] \| Subsequent Event [Member] \| October 2017 Lease Amendment [Member]
Commitment And Contingencies [Line Items]
Operating lease extended additional term	5 days
CFFT Grants [Member]
Commitment And Contingencies [Line Items]
Grants received			$ 500,000

Commitments and Contingencies (Details) $ in Thousands	Dec. 31, 2017 USD ($)
Commitments And Contingencies Disclosure [Abstract]
2018	$ 556
2019	1,234
2020	1,271
2021	1,310
2022	1,349
Thereafter	3,138
Total	$ 8,858

Related Party Transactions - Additional Information (Details Textual) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Related Party Transaction [Line Items]
Stock compensation expense recognized	$ 2,170,000	$ 300,000	$ 99,000
Providence Therapeutics, Inc [Member] \| Research Collaboration and License Agreement [Member]
Related Party Transaction [Line Items]
Upfront fee received		500,000
Revenue related to amortization of upfront payment	1,000,000	500,000
Accounts receivable, outstanding	0	$ 0
Stock compensation expense recognized	$ 1,500,000
Providence Therapeutics, Inc [Member] \| Research Collaboration and License Agreement [Member] \| President and Chief Executive Officer [Member]
Related Party Transaction [Line Items]
Ownership interest	5.70%	10.00%

Litigation (Details Textual)	12 Months Ended
Litigation (Details Textual)	Dec. 31, 2017
Israel Litigation [Member]
Loss Contingencies [Line Items]
Lawsuit filing date	February 25, 2018
Name of plaintiff	Joseph Payne, a current Director and former CEO of the Company
Name of defendant	Company, its board of directors, Dr. Chivukula, and certain officers
Allegations	The separation agreement the Company entered into with a resigning officer, Dr. Chivukula, was unlawful and void, and seeking a restraining order and temporary remedies against the Company
California State Court Litigation [Member}
Loss Contingencies [Line Items]
Lawsuit filing date	March 27, 2018
Name of plaintiff	Company and Arcturus Therapeutics, Inc
Name of defendant	Joseph E. Payne
Allegations	Payne (1) breached his confidentiality and employment agreements, (2) breached his fiduciary duties to the plaintiffs during his service as President and CEO of the plaintiffs and as a director of the plaintiffs’ respective boards of directors, (3) interfered with contractual relations by encouraging Dr. Chivukula, a resigning officer, to breach the consulting agreement entered into by and between Dr. Chivukula and Arcturus Therapeutics, Inc. and the voting trust agreement entered into by and between Dr. Chivukula and the Company, and (4) interfered with prospective business advantage by encouraging Company shareholders to vote against the ratification of the appointment of Ernst & Young LLP in the United States as the Company’s independent auditor.
California Federal Court Litigation [Member]
Loss Contingencies [Line Items]
Lawsuit filing date	April 19, 2018
Name of plaintiff	Arcturus Therapeutics, Inc
Name of defendant	Joseph E. Payne; Peter Farrell; Andrew Sassine; Bradley Sorenson; James Barlow
Allegations	Defendants have violated and continue to violate Section 13(d) of the Exchange Act, 15 U.S.C. §78m(d), and Regulation 13D by failing to disclose in Schedule 13D filings the existence of group agreements to buy, sell, or vote shares of the Company and effect a change in the composition of the Company’s board of directors.

Subsequent Events (Details Textual) - Subsequent Event [Member]	1 Months Ended
	Feb. 28, 2018 USD ($) shares
Subsequent Event [Line Items]
Cash payment	$ 335,000
Stock issued for services \| shares	183,137
Cash payment for scientific advisory services	$ 100,000

Fair Value Measurements - (Details Textual) - USD ($)	Dec. 31, 2017	Dec. 31, 2016
Fair Value, Measurements, Recurring [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets measured at fair value	$ 10,632,000	$ 0

Income Taxes (Details 2) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Reconciliation Of Unrecognized Tax Benefits Excluding Amounts Pertaining To Examined Tax Returns Roll Forward
Beginning balance of unrecognized tax benefits	$ 0.4	$ 0.4	$ 0.4
Ending balance of unrecognized tax benefits	$ 0.4	$ 0.4	$ 0.4