Arcturus Therapeutics 10-Q 13 May 19 2019 Q1 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	3 Months Ended
	Mar. 31, 2019	May 07, 2019
Document And Entity Information [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Mar. 31, 2019
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	Q1
Trading Symbol	ARCT
Entity Registrant Name	Arcturus Therapeutics Ltd.
Entity Central Index Key	0001566049
Current Fiscal Year End Date	--12-31
Entity Filer Category	Non-accelerated Filer
Entity Small Business	true
Entity Emerging Growth Company	false
Entity Common Stock, Shares Outstanding		10,761,523

CONDENSED CONSOLIDATED BALANCE

CONDENSED CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Current assets:
Cash and cash equivalents	$ 31,220	$ 36,709
Accounts receivable	4,457	4,481
Prepaid expenses and other current assets	929	638
Total current assets	36,606	41,828
Property and equipment, net	2,016	1,975
Operating lease right-of-use asset	5,690
Equity-method investment		288
Non-current restricted cash	107	107
Total assets	44,419	44,198
Current liabilities:
Accounts payable	4,118	2,398
Accrued liabilities	2,766	3,907
Deferred revenue	7,728	6,272
Total current liabilities	14,612	12,577
Deferred revenue, net of current portion	8,025	7,534
Long-term debt	9,945	9,911
Operating lease liability, net of current portion	5,483
Deferred rent		534
Total liabilities	38,065	30,556
Shareholders' equity
Ordinary shares: NIS 0.07 par value; 30,000 shares authorized, 10,762 issued, 10,719 outstanding and 43 held in treasury at March 31, 2019; NIS 0.07 par value; 30,000 shares authorized, 10,762 issued, 10,719 outstanding and 43 held in treasury at December 31, 2018	214	214
Additional paid-in capital	58,701	58,302
Accumulated deficit	(52,561)	(44,874)
Total shareholders' equity	6,354	13,642
Total liabilities and shareholders' equity	$ 44,419	$ 44,198

CONDENSED CONSOLIDATED BALANC_2

CONDENSED CONSOLIDATED BALANCE SHEETS (Parenthetical) - ₪ / shares	Mar. 31, 2019	Dec. 31, 2018
Statement Of Financial Position [Abstract]
Common stock, par value	₪ 0.07	₪ 0.07
Common stock, shares authorized	30,000,000	30,000,000
Treasury shares	43,000	43,000
Common stock, shares issued	10,762,000	10,762,000
Common stock, shares outstanding	10,719,000	10,719,000

CONDENSED CONSOLIDATED STATEMEN

CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE LOSS - USD ($) shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Statement Of Income And Comprehensive Income [Abstract]
Collaboration revenue	$ 4,350	$ 2,367
Operating expenses:
Research and development, net	7,324	3,941
General and administrative	3,534	5,098
Total operating expenses	10,858	9,039
Net loss from operations	(6,508)	(6,672)
Loss from equity-method investment	(288)
Finance (expense) income, net	(88)	101
Net loss	$ (6,884)	$ (6,571)
Net loss per share, basic and diluted	$ (0.68)	$ (0.66)
Weighted-average shares outstanding, basic and diluted	10,095	10,028
Comprehensive loss:
Net loss	$ (6,884)	$ (6,571)
Unrealized loss on short-term investments		(2)
Comprehensive loss	$ (6,884)	$ (6,573)

CONDENSED CONSOLIDATED STATEM_2

CONDENSED CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY - USD ($) shares in Thousands, $ in Thousands	Total	Ordinary Shares [Member]	Additional Paid-In Capital [Member]	Accumulated Other Comprehensive Loss [Member]	Accumulated Deficit [Member]
Balance at Dec. 31, 2017	$ 33,794	$ 212	$ 56,674	$ (3)	$ (23,089)
Balance (in shares) at Dec. 31, 2017		10,699
Net loss	(6,571)				(6,571)
Unrealized loss on short-term investments	(2)			(2)
Share-based compensation	26		26
Issuance of common shares upon exercise of share options	304	$ 1	303
Issuance of common shares upon exercise of share option (in shares)		39
Balance at Mar. 31, 2018	27,551	$ 213	57,003	$ (5)	(29,660)
Balance (in shares) at Mar. 31, 2018		10,738
Balance at Dec. 31, 2018	13,642	$ 214	58,302		(44,874)
Balance (in shares) at Dec. 31, 2018		10,762
Net loss	(6,884)				(6,884)
Share-based compensation	399		399
Effect of adoption of ASC 606	(803)				(803)
Balance at Mar. 31, 2019	$ 6,354	$ 214	$ 58,701		$ (52,561)
Balance (in shares) at Mar. 31, 2019		10,762

CONDENSED CONSOLIDATED STATEM_3

CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
OPERATING ACTIVITIES:
Net loss	$ (6,884)	$ (6,571)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	172	111
Share-based compensation expense	399	26
Non-cash interest expense	34
Loss from equity-method investment	288
Changes in operating assets and liabilities
Accounts receivable	24	(697)
Prepaid expense and other assets	(291)	371
Accounts payable	1,586	852
Accrued liabilities	(1,891)	(46)
Right of use asset and liability, net	8
Deferred revenue	1,144	5,593
Net cash used in operating activities	(5,411)	(361)
INVESTING ACTIVITIES:
Proceeds from maturities of short-term investments		19,294
Purchases of short-term investments		(7,707)
Acquisition of property and equipment	(78)	(362)
Net cash (used in) provided by investing activities	(78)	11,225
FINANCING ACTIVITIES:
Proceeds from exercise of share options		294
Net cash provided by financing activities		294
NET (DECREASE) INCREASE IN CASH, CASH EQUIVALENTS AND RESTRICTED CASH	(5,489)	11,158
Cash, cash equivalents and restricted cash at beginning of the period	36,816	25,238
Cash, cash equivalents and restricted cash at end of the period	31,327	36,396
Supplemental disclosure of cash flow information
Cash paid for interest	167
Non-cash investing activities
Purchase of property and equipment in accounts payable	$ 134	$ 320

Description of Business, Basis

Description of Business, Basis of Presentation and Summary of Significant Accounting Policies	3 Months Ended
	Mar. 31, 2019
Accounting Policies [Abstract]
Description of Business, Basis of Presentation and Summary of Significant Accounting Policies	Note 1. Description of Business, Basis of Presentation and Summary of Significant Accounting Policies Description of Business Arcturus Therapeutics Ltd. and its subsidiaries (referred to as the “Company”) is a RNA medicines company focused on significant opportunities in rare, liver, and respiratory diseases. The Company’s key proprietary technology has the potential to address the major hurdles in RNA development, namely the effective and safe delivery of RNA therapeutics to disease-relevant target tissues. Basis of Presentation The accompanying condensed consolidated financial statements include the accounts of Arcturus Therapeutics Ltd. and its subsidiaries and are unaudited. All intercompany accounts and transactions have been eliminated in consolidation. These condensed consolidated financial statements have been prepared in accordance with U.S. generally accepted accounting principles (“GAAP”) for interim financial information. Accordingly, they do not include all of the information and footnotes required by GAAP for complete financial statements. In management’s opinion, the accompanying condensed consolidated financial statements reflect all adjustments, consisting of normal recurring adjustments, considered necessary for a fair presentation of the results for the interim periods presented. Interim financial results are not necessarily indicative of results anticipated for the full year. These condensed consolidated financial statements should be read in conjunction with the audited financial statements and footnotes included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2018. These condensed consolidated financial statements are prepared in accordance with GAAP with United States Dollars (“USD”) as the functional currency, which requires management to make estimates and assumptions regarding the valuation of certain debt and equity instruments, the disclosure of contingent assets and liabilities at the date of the financial statements and Unless the context otherwise requires, references to the “Company” and “Arcturus” refer to Arcturus Therapeutics Ltd. and its subsidiaries. Going Concern The Company’s activities since inception have consisted principally of performing research and development activities, general and administration 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. The Company is a pre-clinical bioscience company that is dependent on obtaining external equity and debt financings to fund its operations. Historically, the Company’s primary sources of financing have been through the sale of its securities, through issuance of debt and through collaboration agreements. The Company raised $10.0 million in gross proceeds from a long-term debt agreement entered into on October 12, 2018 with Western Alliance Bank (Note 5). In addition, on October 15, 2018, the Company entered into a Sales Agreement (the “Sales Agreement”) with Leerink Partners LLC (“Leerink”), pursuant to which it may sell from time to time, at its option, up to an aggregate of $30.0 million of the Company’s Ordinary Shares through Leerink, as sales agent. Research and development activities have required significant capital investment since the Company’s inception. The Company expects its 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 experienced net losses since its inception and as of March 31, 2019 has an accumulated deficit of $52.6 million. Recent Developments The Company has initiated a process to redomicile from an Israeli limited company to a Delaware corporation (the “Redomiciliation”). The Redomiciliation is subject to the approval of the Company’s shareholders via proxy vote, the Tel-Aviv District Court (the “Israeli Court”) approval and approval of the listing of the shares in the Delaware corporation by the NASDAQ Stock Market LLC (“Nasdaq”), among other conditions precedent. On February 11, 2019, the Company filed an application with the Israeli Court to approve the convening of a general shareholders meeting of the Company for the approval of the Redomiciliation pursuant to Sections 350 and 351 of the Israeli Companies Law (the “Companies Law”). Following the Israeli Court approval dated March 13, 2019, the Company filed with the SEC a registration statement on Form S-4 (the “Form S-4”), which included a joint proxy statement/prospectus for the convening of the general shareholder meeting, scheduled to be held on May 17, 2019, as described in the Form S-4. If the general shareholders meeting results in the approval of the Redomiciliation, the Company will then approach the Israeli Court and request its approval of the Redomiciliation. In connection with the Redomiciliation, the Company entered into a share exchange agreement (the “Exchange Agreement”) with a special-purpose company, Arcturus Therapeutics Holdings Inc. (“NewCo”). In furtherance of the Redomiciliation, and pursuant to the terms of the Exchange Agreement, the holders of Ordinary Shares of the Company as of a future record date and the holders of options to purchase Ordinary Shares of the Company as of the same record date will transfer their Ordinary Shares of the Company and options to purchase Ordinary Shares of the Company, respectively, to NewCo and, in exchange thereof, will receive one share of common stock of NewCo for each ordinary share of the Company and an option to purchase one share of common stock of NewCo in exchange for each ordinary share of the Company underlying the existing option to be so exchanged, respectively. The Company intends the common stock of NewCo to be listed on NASDAQ. Upon consummation of the transactions contemplated by the Share Exchange Agreement, it is expected that the Company’s Ordinary Shares will be delisted from trading on NASDAQ, and the Company is expected to become a private company (as defined in the Companies Law) wholly-owned by NewCo. Pursuant to the Exchange Agreement, and as disclosed in the Form S-4, the Company also has the right, exercisable in its sole discretion and subject to the conditions precedent set forth therein, to transfer all of the shares of Arcturus Therapeutics Inc. (“Arcturus Sub”), a wholly-owned subsidiary of the Company, to NewCo through a reduction of the Company’s equity and the distribution of a dividend-in-kind, such that Arcturus Sub and the Company shall each become a wholly-owned and direct subsidiary of NewCo. The Company will determine if it will proceed with this second step prior to December 31, 2019. 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 the Company’s nucleic acid-focused technology. Revenue Recognition Effective January 1, 2019, the Company adopted ASU 2014-09, Revenue from Contracts with Customers (Topic 606) , or Topic 606, The terms of the Company’s collaborative research and development agreements include 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, option exercise fees, other contingent payments for the achievement of defined collaboration objectives and certain preclinical, clinical, regulatory and sales-based events, as well as royalties on sales of commercialized products. Arrangements that include up-front payments are recorded as deferred revenue upon receipt or when due and may require deferral of revenue recognition to a future period until the Company perform obligations under these arrangements. The Company records research funding as accounts receivable when the right to consideration is unconditional. The event-based milestone payments represent variable consideration, and the Company uses the most likely amount method to estimate this variable consideration because the Company will either receive the milestone payment or will not, which makes the potential milestone payment a binary event. The most likely amount method requires the Company to determine the likelihood of earning the milestone payment. Given the high degree of uncertainty around achievement of these milestones, the Company determines the milestone amounts to be fully constrained and does not recognize revenue until the uncertainty associated with these payments is resolved. The Company will recognize revenue from sales-based royalty payments when or as the sales occur. The Company will re-evaluate the transaction price in each reporting period as uncertain events are resolved and other changes in circumstances occur. A performance obligation is a promise in a contract to transfer a distinct good or service to the collaborative partner and is the unit of account in Topic 606. A contract’s transaction price is allocated to each distinct performance obligation based on relative standalone selling price and recognized as revenue when, or as, the performance obligation is satisfied. Under Topic 606, the Company elected to use the practical expedients permitted related to adoption, which does not require the Company to disclose certain information regarding certain remaining performance obligations as of the end of the reporting period. Topic 606 is applicable for revenue recognized in accordance with the p See Note 2, “Collaboration Revenue” for specific details surrounding the Company’s collaboration arrangements. Leases In February 2016, the FASB issued ASU 2016-02, Leases (Topic 842), which requires lessees to recognize most leases on the balance sheet as lease liabilities with corresponding right-of-use assets and to disclose key information about leasing arrangements. The Company adopted Topic 842 on its effective date in the first quarter of 2019 using a modified retrospective approach. The Company elected the available package of practical expedients upon adoption, which allowed it to carry forward historical assessment of whether existing agreements contained a lease and the classification of existing operating leases. The Company continues to report its financial position as of December 31, 2018 under the former lease accounting standard (Topic 840) in the condensed consolidated balance sheet The adoption impact was due to the recognition of an operating lease liability with a corresponding right-of-use asset based on the present value of remaining minimum lease payments. A reduction of the right-of-use asset was recorded to reflect the balance of the deferred rent obligation and there was no impact to retained earnings. Research and Development, Net Research and development costs are expensed as incurred. 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. Statement of Cash Flows The following table provides a reconciliation of cash and cash equivalents and restricted cash reported within the condensed consolidated balance sheet to the total of the same such amounts shown in the condensed consolidated statement of cash flows: (in thousands) March 31, 2019 March 31, 2018 Cash and cash equivalents $ 31,220 $ 36,289 Non-current restricted cash 107 107 Total cash, cash equivalents and restricted cash shown in the statement of cash flows $ 31,327 $ 36,396 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 treas ury-stock method. Dilutive ordinary shares are comprised of share options. No dividends were declared or paid during the reported periods. Recently Adopted Accounting Pronouncements Revenue from Contracts with Customers In May 2014, the Financial Accounting Standards Board (FASB) issued Topic 606, which supersedes nearly all existing revenue recognition guidance under GAAP. The FASB subsequently issued amendments to Topic 606 that have the same effective date and transition date. The Company adopted this new guidance, effective January 1, 2019, using the modified retrospective transition method, in which the standard is applied as of the date of initial adoption. The Company recorded the cumulative effect of initially applying the standard as an adjustment to the opening balance of accumulated deficit. The adoption of the new revenue recognition guidance resulted in an increase of $0.8 million to deferred revenue and an increase of $0.8 million to accumulated deficit as of January 1, 2019. The change in revenue was due to a change in how the Company accounts for changes in the measure of progress and changes to the transaction price and for the recognition of revenue. Under Topic 605, the Company accounted for changes to the measure of progress and changes to the transaction price prospectively. Topic 606 requires companies to account for a change to the measure of progress or a change to the transaction price as a cumulative catch-up in the period of change. There were no other impacts upon the adoption of Topic 606. The Company will apply the standard to all new contracts initiated on or after the effective date. Under prior guidance, collaboration revenue recognized would have been $4.1 million for the three months ended March 31, 2019, which is $0.3 million lower than the amount recognized under current guidance. Leases In February 2016, the FASB issued Accounting Standards Update ("ASU") 2016-02, Leases (Topic 842) In July 2018, the FASB issued ASU 2018-11, Leases (Topic 842): Targeted Improvements provides entities an optional transition method to apply the new guidance as of the adoption date, rather than as of the earliest period presented. In transition, entities may also elect a package of practical expedients that must be applied in its entirety to all leases commencing before the effective date, unless the lease was modified, to not reassess (a) the existence of a lease, (b) lease classification or (c) determination of initial direct costs, which effectively allows entities to carryforward accounting conclusions under previous U.S. GAAP. The Company adopted ASU 2016-02, using the optional transition method and electing the package of practical expedients described above on January 1, 2019. Due to the adoption, the Company recognized a new lease liability on the Company's consolidated balance sheet for its operating lease of office and lab space of $6.2 million on January 1, 2019, with a corresponding right-of-use asset of $5.7 million based on the present value of the remaining minimum rental payments. See Note 11 for further discussion.

Collaboration Revenue

Collaboration Revenue	3 Months Ended
	Mar. 31, 2019
Collaboration Agreements [Abstract]
Collaboration Revenue	Note 2. Collaboration Revenue 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, reimbursement for research and development activities, option exercise fees, other contingent payments for the achievement of defined collaboration objectives and certain preclinical, clinical, regulatory and sales-based events, as well as royalties on sales of commercialized products. 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 or second 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 presents changes during the three months ended March 31, 2019 in the balances of contract assets, including receivables from collaborative partners, and contract liabilities, including deferred revenue, as compared to what was disclosed in the Company’s Annual Report. (in thousands) Contract Assets Balance at December 31, 2018 $ 4,480 Additions 3,611 Deductions (3,634 ) Balance at March 31, 2019 $ 4,457 (in thousands) Contract Liabilities Balance at December 31, 2018 $ 13,806 Additions for advanced billings 5,868 Additions for performance obligations to be satisfied in current and future periods in connection with Topic 606 adoption 803 Deductions for performance obligations satisfied in current period (4,724 ) Balance at March 31, 2019 $ 15,753 The following paragraphs provide information regarding the nature and purpose of the Company’s most significant collaboration arrangements. Collaboration Partner – Janssen In October 2017 the Company entered into a research collaboration and license agreement with Janssen (the “2017 Agreement”). The 2017 Agreement allocated discovery, development, funding obligations, and ownership of related intellectual property among the Company and Janssen. The Company received an upfront payment of $7.7 million and may receive preclinical, development and sales milestone payments of $56.5 million, as well as royalty payments on any future licensed product sales. Janssen began reimbursing the Company for research costs during the first quarter of 2019 upon the completion of the first of three research periods. Janssen may also pay option exercise fees within the $1.0 million to $5.0 million range per target. Janssen 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 2017 Agreement includes an exclusivity period. Accounting Analysis under ASC 606 In evaluating the 2017 Agreement in accordance with ASC Topic 606, the Company concluded that the contract counterparty, Janssen, is a customer. The Company identified the following performance obligations as of the inception of the Agreement: (i) research services, (ii) license to use Arcturus technology and (iii) participation in the Joint Research Committee. The Company concluded that the performance obligations are highly interrelated and consequently do not have any value on a standalone basis. Accordingly, they are determined to represent a single performance obligation. The Company concluded that Janssen’s options to select additional collaboration targets and to license rights to selected targets are not priced at a discount and therefore do not represent performance obligations for which the transaction price would be allocated. At inception of the contract, the transaction price included the $7.7 million upfront consideration received and budgeted reimbursable out-of-pocket costs of $18.2 million. None of the development and commercialization milestones were included in the transaction price, as all milestone amounts were fully constrained. As part of its evaluation of the constraint, the Company considered numerous factors, including that receipt of the milestones is outside the control of the Company and contingent upon success in future clinical trials and the collaborator’s efforts. Any consideration related to sales-based royalties will be recognized when the related sales occur, provided that the reported sales are reliably measurable, and the Company has no remaining performance obligations, as such sales were determined to relate predominantly to the license granted to Janssen and therefore have also been excluded from the transaction price. As of March 31, 2019, the remaining transaction price of $24.2 million is expected to be recognized over the remaining research period of 12 months. The Company will re-evaluate the transaction price in each reporting period as uncertain events are resolved and other changes in circumstances occur. For the three months ended March 31, 2019, no adjustments were made to the transaction price. As the Company determined that only a single performance obligation exists, no allocation of the transaction price is necessary. The transaction price is recorded as deferred revenue in the Company’s balance sheet and is recognized as revenue under the proportional performance method of revenue recognition in accordance with the Company’s established budget of costs to be incurred. Total deferred revenue as of March 31, 2019 and December 31, 2018 for Janssen was $6.3 million and $6.5 million, respectively. The Company recognized revenue of $0.5 million and $0.1 million for the three months ended March 31, 2019 and 2018, respectively. No transition adjustment was necessary upon adoption of Topic 606. Collaboration Partner – Ultragenyx In October 2015 the Company entered into a research collaboration and license agreement with Ultragenyx (the “Ultragenyx Agreement”), whereby Arcturus grants to Ultragenyx a co-exclusive license under Arcturus technology and shall be in effect only during the reserve target exclusivity term as discuss in the following paragraphs. During the initial phase of the collaboration, the Company will design and optimize therapeutics for certain rare disease targets. Ultragenyx has the option under the Ultragenyx Agreement to add additional rare disease targets during the collaborative development period. Additionally, during the collaborative development period, the Company will participate with Ultragenyx in a joint steering committee. The Ultragenyx Agreement also includes an initial exclusivity period with an option to extend this period. For each program, Ultragenyx will reimburse the Company for all internal and external development costs incurred, pursuant to the Ultragenyx Agreement, and if Ultragenyx achieves certain, clinical, regulatory and sales milestones, then the Company is eligible to receive royalty payments. As part of the Ultragenyx Agreement, Ultragenyx paid an upfront fee of $10.0 million and agreed to certain research and development funding obligations. The Company is also entitled to certain additional payments upon exercise of the Ultragenyx expansion option or exclusivity extension (if any), and for costs incurred by the Company in conducting the activities assigned 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, Ultragenyx 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 Ultragenyx exercises its option, Ultragenyx will pay the Company a one-time option exercise fee that increases based upon the number of development targets selected by Ultragenyx. The agreement includes potential milestone payments for selected targets from Ultragenyx to the Company. The current potential milestone payment for the remaining targets as of March 31, 2019 is $139.0 million. Ultragenyx will pay royalties as a single-digit percentage of net sales on a product-by-product and country-by-country basis during the applicable royalty term. As of March 31, 2019, the Company has not yet reached the clinical phase of the contract. In 2018, the Company signed an amendment with Ultragenyx, that may reduce option exercise fees, milestone payments and/or royalty rates dependent on whether a development target or product is not covered by a patent directed to a chemistry methodology to increase mRNA half-life. During 2017, the Company entered into an amendment with Ultragenyx to add one year to the exclusivity period for the reserved 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 allows Ultragenyx the opportunity to review and comment on its filings and prosecution efforts of pending Company patents that relate to Ultragenyx chemistry. During the fourth quarter of 2018, Ultragenyx extended the exclusivity on a specified number of reserved targets for an additional year with an annual reserve target list maintenance fee of $1.5 million. Accounting Analysis under ASC 606 In evaluating the Ultragenyx agreement in accordance with ASC Topic 606, the Company concluded that the contract counterparty, Ultragenyx, is a customer. The Company identified the following performance obligations as of the inception of the Agreement: (i) research services, (ii) license to use Arcturus technology, (iii) exclusivity and (iv) participation in the Joint Steering Committee. The Company concluded that the performance obligations are highly interrelated and consequently do not have any value on a standalone basis. Accordingly, they are determined to represent a single performance obligation. The Company concluded that Ultragenyx’s options to extend exclusivity and options to select additional collaboration targets and to license rights to selected targets are not priced at a discount and therefore do not represent performance obligations for which the transaction price would be allocated. At inception of the contract, the transaction price included only the upfront consideration received. The Company concluded that the reimbursement of labor and expenses qualifies for the practical expedient under Topic 606, which allows the Company to recognize revenue in the amount for which it has a right to invoice if the Company’s right to consideration is an amount that corresponds directly to the value to the customer of the performance completed to date. Therefore under the practical expedient the Company is not required to determine the transaction price, allocate the transaction price and determine the timing of revenue recognition for the reimbursement of labor and expenses. None of the development and commercialization milestones were included in the transaction price, as all milestone amounts were fully constrained. As part of its evaluation of the constraint, the Company considered numerous factors, including that the consideration is outside the control of the Company and contingent upon success in future clinical trials, approval from the Food and Drug Administration (“FDA”) and the collaborator’s efforts. Any consideration related to sales-based royalties will be recognized when the related sales occur, provided that the reported sales are reliably measurable and the Company has no remaining performance obligations, as such sales were determined to relate predominantly to the license granted to Ultragenyx and therefore have also been excluded from the transaction price. The Company will re-evaluate the transaction price in each reporting period as uncertain events are resolved and other changes in circumstances occur. For the three months ended March 31, 2019, no adjustments were made to the transaction price. As the Company determined that only a single performance obligation exists, no allocation of the transaction price is necessary. The upfront payment was recorded as deferred revenue in the Company’s balance sheet upon receipt and is currently being recognized as revenue on a straight-line basis over the estimated 47-month research period, which approximates the timing in which performance obligations are satisfied. As of March 31, 2019, the research period is expected to end by September 30, 2019. Upon execution of the 2017 amendment, the $2.0 million payment was added to the transaction price and through the transition to Topic 606 a cumulative catch-up entry was made. The exclusivity extension fee received by the Company during the fourth quarter of 2018 was recorded as deferred revenue and is being recognized as revenue on a straight-line basis over the one-year period that the exclusivity is provided. Total deferred revenue as of March 31, 2019 and December 31, 2018 for Ultragenyx was $2.4 million and $2.7 million, respectively. The Company recognized revenue of $1.4 million and $1.5 million for the three months ended March 31, 2019 and 2018, respectively. Upon adoption of Topic 606, the Company reversed $0.8 million of previously recorded revenue related to Ultragenyx through an increase to deferred revenue and a decrease to beginning retained earnings. The adjustment was due to a change in the way the Company accounts for updates to the research period over which revenue is recognized as well as accounting for adjustments to the transaction price for exclusivity extensions, such as the $2.0 million amendment. Under Topic 605, the Company accounted for these changes prospectively and under Topic 606 the Company accounts for the changes as a change in estimate recorded as a cumulative catch-up in the period in which the change occurred. Collaboration Partner – CureVac In January 2018, the Company entered into a Development and Option Agreement with CureVac, (the “Development and Option Agreement”). Under the terms of the Development and Option Agreement, the parties have agreed to conduct joint preclinical development programs once CureVac makes a payment to pull down a target on the basis of which CureVac is granted options for taking a license on pre-agreed license terms to develop and commercialize certain products incorporating the Company’s patents and know-how related to delivery technology (the LUNAR® platform) (the “Arcturus Delivery Technology”), and CureVac patents and know-how related to mRNA technology. Subject to certain restrictions, the parties will have an undivided one-half interest in the patents and know-how developed jointly by the parties during the course of the Development and Option Agreement. Pursuant to the terms of the Development and Option Agreement, CureVac will have a number of target options to co-develop from a reserved target list to enter into licenses under the Arcturus Delivery Technology with respect to the development, manufacture and commercialization of licensed products (which can include products identified for development by the Company unless the Company is permitted by the terms of the Development and Option Agreement to place such products on a restricted list). A separate notice and fee will be required for each license agreement. If the target to which the license agreement relates is chosen by the parties for co-development under the Co-Development Agreement (which is defined below and discussed in the following paragraph) the license agreement will terminate as such programs will be covered under the Co-Development Agreement discussed below, and therefore CureVac will be given a credit for any exercise fees, milestone payments already paid and all other payments made in relation to the license agreement towards future such payments incurred with respect to future licenses under the Arcturus Delivery Technology. Prior to expiration of the initial term of 8 years, the Agreement also includes an option to extend the term on an annual basis for up to 3 years and subject to payment by CureVac to Arcturus of a non-refundable annual extension fee. The agreement included potential milestone payments for selected targets from CureVac to the Company. The current potential milestone payment for the remaining target as of March 31, 2019 is $14.0 million for rare disease targets and $23.0 million for non-rare disease targets. CureVac will pay royalties as a percentage of net sales on a product-by-product and country-by-country basis during the applicable royalty term in the low single-digit range. As of March 31, 2019, the Company has not yet reached the clinical phase of the contract. Pursuant to a May 2018 amendment to the Development and Option Agreement (as amended and restated on September 28, 2018), the Company increased the number of targets available to CureVac under the Development and Option Agreement and agreed upon the license forms to be executed upon selection of the targets by CureVac. Concurrently with the Development and Option Agreement, the Company entered into a Co-Development and Co-Commercialization Agreement (the “Co-Development Agreement”). However, on February 11, 2019, the Company announced the termination of the obligations of CureVac for the preclinical development of ARCT-810, effective 180 days from February 5, 2019 and the re-assumption by the Company of the worldwide rights thereto. CureVac believes it is not obligated to continue funding any preclinical expenses for the OTC (which is defined in the following paragraph) program after February 5, 2019 and through the August 5, 2019 termination date as stated in the Co-Development Agreement. The Company does not believe that CureVac’s position is consistent with the terms of the Co-Development Agreement and is engaged with CureVac to determine a resolution. The Company is seeking a resolution in the manner set forth in the Co-Development Agreement. Arcturus will reassume 100% global rights for its flagship asset, clinical development candidate ARCT-810, a messenger RNA (mRNA) drug to treat ornithine transcarbamylase (“OTC”) deficiency. ARCT-810 was previously subject to equal cost sharing between Arcturus and CureVac under the Co-Development Agreement. CureVac elected not to continue its obligations for the preclinical development of ARCT-810 under and pursuant to the terms of the agreement. Under the terms of the Co-Development Agreement, the parties collaborated to develop and commercialize mRNA-based products for treating OTC deficiency, incorporating CureVac’s mRNA technology, the Arcturus’ mRNA technology and the Arcturus Delivery Technology. The overall collaboration with CureVac was managed by a joint steering committee. Pursuant to the Co-Development Agreement, the Company and CureVac shared equally the internal costs and third-party costs incurred to conduct preclinical development, subject to exceptions specified in the Co-Development Agreement for specified manufacturing costs and costs in the parties’ respective development plans, among others. The parties also continue to have the option to co-develop two mRNA programs for CureVac and one mRNA program for the Company. The Company concluded that the contracts should be accounted for on a combined basis due to their being negotiated and signed concurrently as well as the interoperability between the two agreements. Accounting Analysis under ASC 606 In evaluating the CureVac Development and Option Agreement and Co-Development Agreement in accordance with ASC Topic 606, the Company concluded that the contract counterparty, CureVac, is a customer. The Company identified the following performance obligations as of the inception of the Agreement: (i) research services, (ii) license to use Arcturus technology, (iii) exclusivity and (iv) participation in the Joint Steering Committee. The Company concluded that the performance obligations are highly interrelated and consequently do not have any value on a standalone basis. Accordingly, they are determined to represent a single performance obligation. The Company concluded that CureVac’s options to extend the research term and options to select additional collaboration targets and to license rights to selected targets are not priced at a discount and therefore do not represent performance obligations for which the transaction price would be allocated. At inception of the contract, the transaction price included only the $5.0 million upfront consideration received. The Company concluded that the reimbursement of labor and expenses within the Development and Option Agreement qualifies for the practical expedient under Topic 606 which allows the Company to recognize revenue in the amount for which it has a right to invoice if the Company’s right to consideration is an amount that corresponds directly to the value to the customer of the performance completed to date. Therefore under the practical expedient the Company is not required to determine the transaction price, allocate the transaction price and determine the timing of revenue recognition for the reimbursement of labor and expenses. None of the development and commercialization milestones were included in the transaction price, as all milestone amounts were fully constrained. As part of its evaluation of the constraint, the Company considered numerous factors, including that receipt of the milestones is outside the control of the Company and contingent upon success in future clinical trials and the collaborator’s efforts. Any consideration related to sales-based royalties will be recognized when the related sales occur, provided that the reported sales are reliably measurable and the Company has no remaining performance obligations, as such sales were determined to relate predominantly to the license granted to CureVac and therefore have also been excluded from the transaction price. As it relates to the Co-Development Agreement, the incremental costs incurred by Arcturus can only be determined based on reported costs provided by CureVac which is outside the control of the Company, and therefore, fully constrained and recognized as incurred. The Company will re-evaluate the transaction price in each reporting period as uncertain events are resolved and other changes in circumstances occur. For the three months ended March 31, 2019, no adjustments were made to the transaction price. As the Company determined that only a single performance obligation exists, no allocation of the transaction price is necessary. The upfront payment of $5 million was recorded as deferred revenue in the Company’s balance sheet upon receipt and is currently being recognized as revenue on a straight-line basis over the eight-year contractual term. Total deferred revenue as of March 31, 2019 and December 31, 2018 for CureVac was $4.2 million and $4.4 million, respectively. The Company recognized revenue of $1.9 million and $0.2 million for the three months ended March 31, 2019 and 2018, respectively. No adjustment was necessary upon adoption of Topic 606

Fair Value Measurements

Fair Value Measurements	3 Months Ended
	Mar. 31, 2019
Fair Value Disclosures [Abstract]
Fair Value Measurements	Note 3. Fair Value Measurements The Company establishes the fair value of its 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 establishes 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, accounts receivable, accounts payable, and accrued liabilities approximate their respective fair values due to their relative short maturities. The carrying amounts of long-term debt for the amount drawn on the Company’s debt facility approximates fair value as the interest rate is variable and reflects current market rates. As of March 31, 2019 and December 31, 2018, all assets measured at fair value on a recurring basis consisted of cash equivalents which were classified within Level 1 of the fair value hierarchy. The fair value of these financial instruments was measured based on quoted prices.

Balance Sheet Details

Balance Sheet Details	3 Months Ended
	Mar. 31, 2019
Balance Sheet Related Disclosures [Abstract]
Balance Sheet Details	Note 4 Prepaid expenses and other current assets consisted of the following as of March 31, 2019 and December 31, 2018: (in thousands) March 31, 2019 December 31, 2018 Prepaid expenses $ 807 $ 546 Other current assets 122 92 Total $ 929 $ 638 Property and equipment, net consisted of the following: (in thousands) March 31, 2019 December 31, 2018 Research equipment $ 2,854 $ 2,711 Computers and software 235 200 Office equipment and furniture 561 527 Leasehold improvements 35 34 Total 3,685 3,472 Less accumulated depreciation and amortization (1,669 ) (1,497 ) Property and equipment, net $ 2,016 $ 1,975 Depreciation and amortization expense was $172,000 and $111,000 Accrued liabilities consisted of the following as of March 31, 2019 and December 31, 2018: (in thousands) March 31, 2019 December 31, 2018 Accrued compensation $ 1,015 $ 974 Refundable fees received — 2,259 Current portion of operating lease liability 750 — Other accrued liabilities 1,001 674 Total $ 2,766 $ 3,907

Debt

Debt	3 Months Ended
	Mar. 31, 2019
Debt Disclosure [Abstract]
Debt	Note 5. Debt Long-term debt with Western Alliance Bank On October 12, 2018, the Company entered into a Loan and Security Agreement with Western Alliance Bank whereby the Company received gross proceeds of $10.0 million under a long-term debt agreement (the “Loan”). The Loan has a maturity date of October 1, 2022 and carries interest at the U.S. prime rate plus 1.25%. The loan has an interest-only period of 19 months, which could be extended by an additional 6 months if certain conditions are met, followed by an amortization period of 30 months, or 24 months if the interest-only period is extended. The Company paid a loan origination fee of $128,000 which was recorded as a debt discount and is being accreted over the term of the Loan. In addition, the Company is required to pay a fee of $350,000 upon certain change of control events. Upon maturity or prepayment, the Company will be required to pay a 3% fee, or a 2% fee if the U.S. Food and Drug Administration accepts certain Investigational New Drug (“IND”) applications prior to maturity. Because acceptance of an IND is outside of the Company’s control, management estimated that the Company will be liable for a fee of 3% of the principal balance, or $300,000 upon repayment or maturity, and such fee is accreted to the debt balance using the effective interest method over the term of the Loan. The Loan is collateralized by all of the assets of the Company, excluding intellectual property, which is subject to a negative pledge. The Loan contains customary conditions of borrowing, events of default and covenants, including covenants that restrict the Company’s ability to dispose of assets, merge with or acquire other entities, incur indebtedness and make distributions to holders of the Company’s capital stock. In addition, the Company is required to maintain at least 50% of its deposit and investment accounts, or $20 million, whichever is lower, with the Western Alliance Bank. The Loan also includes covenants which include the Company’s (1) nomination of a clinical candidate by December 31, 2018, which the Company is in compliance with, and (2) submission of a clinical candidate for Investigational New Drug application (“IND”), made to the U.S. Food and Drug Administration by December 31, 2019 and have it approved by January 31, 2020, provided that, if the Company has received net cash proceeds from sale, on or after October 12, 2018, of the Company’s equity securities in an amount of not less than $15,000,000, then the IND submission date shall be extended to May 31, 2020 and the approval date shall be extended to June 30, 2020. Should an event of default occur, including the occurrence of a material adverse effect, the Company could be liable for immediate repayment of all obligations under the Loan. As of March 31, 2019, the Company is in compliance with all covenants and conditions of the Loan.

Shareholders_ Equity

Shareholders’ Equity	3 Months Ended
	Mar. 31, 2019
Stockholders Equity Note [Abstract]
Shareholders’ Equity	Note 6. Shareholders’ Equity 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 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 622,667 Net Loss per Share Dilutive securities that were not included in the calculation of diluted net loss per share for the quarters ended March 31, 2019 and 2018 as they were anti-dilutive totaled 67,051 and 110,883, respectively. For the quarters ended March 31, 2019 and 2018, the calculation of the weighted-average number of shares outstanding excludes both unvested restricted Ordinary Shares of 622,667 and shares held in treasury of 43,000.

Share-Based Compensation

Share-Based Compensation	3 Months Ended
	Mar. 31, 2019
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Share-Based Compensation	Note 7. 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 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 38,751 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 share split in conjunction with the merger. 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. The Company generally issues new shares upon option exercise. There were 111,251 shares available for future issuance under the 2010 Plan as of March 31, 2019; however, the Company does not intend to issue additional shares under the 2010 Plan. In August 2018, the Company adopted the 2018 Omnibus Equity Incentive Plan (“2018 Plan”). Under the 2018 Plan, the Company is authorized to issue up to a maximum of 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 Three Months Ended March 31, 2019 2018 Expected life (in years) 6.1 7.3 Expected volatility 74.1 % 76.4 % Expected dividend yield — % — % Risk-free interest rate 2.51 % 1.87 % Grant date weighted average fair value $ 3.19 $ 7.94 The following table summarizes the Company’s share option activity Number of Shares Weighted Average Exercise Price Weighted- Average Remaining Contractual Term (Years) Aggregate Intrinsic Value (in thousands) Outstanding - December 31, 2018 1,189,433 $ 7.41 Granted 76,000 * $ 4.80 Exercised — $ — $ — Forfeited/cancelled (38,500 ) $ 8.08 Outstanding - March 31, 2019 1,226,933 $ 6.95 9.02 $ 1,254 Exercisable - March 31, 2019 330,661 $ 6.14 7.60 $ 558 Exercisable and expected to vest - March 31, 2019 1,226,933 $ 6.95 9.02 $ 1,254 * Total options granted during the first quarter of 2019 exclude 160,000 options granted to the Chief Executive Officer and Chief Financial Officer which remain subject to shareholder approval. At March 31, 2019, the total unrecognized compensation cost of $ 4.6 3.1 Share-based compensation expenses included in the Company’s condensed statements of operations and comprehensive loss for the three months ended March 31, 2019 and 2018 were: For the Three Months Ended March 31, (in thousands) 2019 2018 Research and development $ 152 $ 8 General and administrative 247 18 Total $ 399 $ 26 Share-based compensation expense for the three months ended March 31, 2019 excludes expense related to options granted to the Chief Executive Officer and Chief Financial Officer as option grants are subject to shareholder approval.

Leases

Leases	3 Months Ended
	Mar. 31, 2019
Leases [Abstract]
Leases	Note 8. Leases In October 2017, the Company entered into a non-cancellable operating lease agreement for office space adjacent to its previously occupied headquarters. The commencement of the lease began in March 2018 and the lease extends for approximately 84 months from the commencement date with a remaining lease term of six years. 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; however, the Company deemed the extension option not reasonably certain to be exercised and therefore excluded the option from the lease terms. The Company entered into an irrevocable standby letter of credit with the landlord for security 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 non-current restricted cash. Operating lease right-of-use asset and liability on the condensed consolidated balance sheets represent the present value of remaining lease payments over the remaining lease terms. The Company does not allocate lease payments to non-lease components; therefore, payments for common-area-maintenance and administrative services are not included in the operating lease right-of-use asset and liability. The Company uses its incremental borrowing rate to calculate the present value of the lease payments, as the implicit rate in the lease is not readily determinable. As of March 31, 2019, the payments of the operating lease liability were as follows: (in thousands) Remaining Lease Payments 2019 $ 932 2020 1,272 2021 1,310 2022 1,349 2023 1,390 Thereafter 1,745 Total remaining lease payments 7,998 Less: imputed interest (1,765 ) Total operating lease liability $ 6,233 Less: current portion of operating lease liability (750 ) Operating lease liability, net of current portion 5,483 Weighted-average remaining lease term 6 years Weighted-average discount rate 8.4 % Operating lease costs consist of the fixed lease payments included in operating lease liability and are recorded on a straight-line basis over the lease terms. Operating lease costs were $0.3 million for the three months ended March 31, 2019.

Related Party Transactions

Related Party Transactions	3 Months Ended
	Mar. 31, 2019
Related Party Transactions [Abstract]
Related Party Transactions	Note 9. Related Party Transactions Providence In March 2016, the Company entered into a Research Collaboration and License Agreement with a related party, Providence, whose CEO and President is also a shareholder of the Company, to identify and optimize microRNA modulators 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. In July 2018, the Providence Agreement was amended and restated to cover brain neoplasms, breast neoplasms and ovarian neoplasms. Each party is responsible for their own research costs under the agreement, and Providence is responsible for all 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 for FTEs at a specified rate. For the quarters ended March 31, 2019 and 2018, the Company has recognized revenue of $0.3 million and a negligible amount, respectively. Equity-Method Investment In June 2018, the Company completed the sale of its intangible asset related to the ADAIR technology. Pursuant to the asset purchase agreement for ADAIR, the Company received a 30% ownership interest in the common stock of a privately held company in consideration for the sale of the ADAIR technology. As this ownership interest is greater than 20% and one executive of the Company holds a seat on the investee’s board of directors, the Company has the ability to exercise significant influence over the operating and financial policies of this investee; therefore, the Company accounts for this investment as an equity-method investment. The Company has no requirement to invest further in this private company and the ownership percentage may be diluted in the future. The Company has recorded $0.6 million of its share of losses of the investee leaving no equity investment balance as of March 31, 2019.

Description of Business, Basi_2

Description of Business, Basis of Presentation and Summary of Significant Accounting Policies (Policies)	3 Months Ended
	Mar. 31, 2019
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation The accompanying condensed consolidated financial statements include the accounts of Arcturus Therapeutics Ltd. and its subsidiaries and are unaudited. All intercompany accounts and transactions have been eliminated in consolidation. These condensed consolidated financial statements have been prepared in accordance with U.S. generally accepted accounting principles (“GAAP”) for interim financial information. Accordingly, they do not include all of the information and footnotes required by GAAP for complete financial statements. In management’s opinion, the accompanying condensed consolidated financial statements reflect all adjustments, consisting of normal recurring adjustments, considered necessary for a fair presentation of the results for the interim periods presented. Interim financial results are not necessarily indicative of results anticipated for the full year. These condensed consolidated financial statements should be read in conjunction with the audited financial statements and footnotes included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2018. These condensed consolidated financial statements are prepared in accordance with GAAP with United States Dollars (“USD”) as the functional currency, which requires management to make estimates and assumptions regarding the valuation of certain debt and equity instruments, the disclosure of contingent assets and liabilities at the date of the financial statements and Unless the context otherwise requires, references to the “Company” and “Arcturus” refer to Arcturus Therapeutics Ltd. and its subsidiaries.
Going Concern	Going Concern The Company’s activities since inception have consisted principally of performing research and development activities, general and administration 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. The Company is a pre-clinical bioscience company that is dependent on obtaining external equity and debt financings to fund its operations. Historically, the Company’s primary sources of financing have been through the sale of its securities, through issuance of debt and through collaboration agreements. The Company raised $10.0 million in gross proceeds from a long-term debt agreement entered into on October 12, 2018 with Western Alliance Bank (Note 5). In addition, on October 15, 2018, the Company entered into a Sales Agreement (the “Sales Agreement”) with Leerink Partners LLC (“Leerink”), pursuant to which it may sell from time to time, at its option, up to an aggregate of $30.0 million of the Company’s Ordinary Shares through Leerink, as sales agent. Research and development activities have required significant capital investment since the Company’s inception. The Company expects its 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 experienced net losses since its inception and as of March 31, 2019 has an accumulated deficit of $52.6 million.
Recent Developments	Recent Developments The Company has initiated a process to redomicile from an Israeli limited company to a Delaware corporation (the “Redomiciliation”). The Redomiciliation is subject to the approval of the Company’s shareholders via proxy vote, the Tel-Aviv District Court (the “Israeli Court”) approval and approval of the listing of the shares in the Delaware corporation by the NASDAQ Stock Market LLC (“Nasdaq”), among other conditions precedent. On February 11, 2019, the Company filed an application with the Israeli Court to approve the convening of a general shareholders meeting of the Company for the approval of the Redomiciliation pursuant to Sections 350 and 351 of the Israeli Companies Law (the “Companies Law”). Following the Israeli Court approval dated March 13, 2019, the Company filed with the SEC a registration statement on Form S-4 (the “Form S-4”), which included a joint proxy statement/prospectus for the convening of the general shareholder meeting, scheduled to be held on May 17, 2019, as described in the Form S-4. If the general shareholders meeting results in the approval of the Redomiciliation, the Company will then approach the Israeli Court and request its approval of the Redomiciliation. In connection with the Redomiciliation, the Company entered into a share exchange agreement (the “Exchange Agreement”) with a special-purpose company, Arcturus Therapeutics Holdings Inc. (“NewCo”). In furtherance of the Redomiciliation, and pursuant to the terms of the Exchange Agreement, the holders of Ordinary Shares of the Company as of a future record date and the holders of options to purchase Ordinary Shares of the Company as of the same record date will transfer their Ordinary Shares of the Company and options to purchase Ordinary Shares of the Company, respectively, to NewCo and, in exchange thereof, will receive one share of common stock of NewCo for each ordinary share of the Company and an option to purchase one share of common stock of NewCo in exchange for each ordinary share of the Company underlying the existing option to be so exchanged, respectively. The Company intends the common stock of NewCo to be listed on NASDAQ. Upon consummation of the transactions contemplated by the Share Exchange Agreement, it is expected that the Company’s Ordinary Shares will be delisted from trading on NASDAQ, and the Company is expected to become a private company (as defined in the Companies Law) wholly-owned by NewCo. Pursuant to the Exchange Agreement, and as disclosed in the Form S-4, the Company also has the right, exercisable in its sole discretion and subject to the conditions precedent set forth therein, to transfer all of the shares of Arcturus Therapeutics Inc. (“Arcturus Sub”), a wholly-owned subsidiary of the Company, to NewCo through a reduction of the Company’s equity and the distribution of a dividend-in-kind, such that Arcturus Sub and the Company shall each become a wholly-owned and direct subsidiary of NewCo. The Company will determine if it will proceed with this second step prior to December 31, 2019.
Segment Information	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 the Company’s nucleic acid-focused technology.
Revenue Recognition	Revenue Recognition Effective January 1, 2019, the Company adopted ASU 2014-09, Revenue from Contracts with Customers (Topic 606) , or Topic 606, The terms of the Company’s collaborative research and development agreements include 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, option exercise fees, other contingent payments for the achievement of defined collaboration objectives and certain preclinical, clinical, regulatory and sales-based events, as well as royalties on sales of commercialized products. Arrangements that include up-front payments are recorded as deferred revenue upon receipt or when due and may require deferral of revenue recognition to a future period until the Company perform obligations under these arrangements. The Company records research funding as accounts receivable when the right to consideration is unconditional. The event-based milestone payments represent variable consideration, and the Company uses the most likely amount method to estimate this variable consideration because the Company will either receive the milestone payment or will not, which makes the potential milestone payment a binary event. The most likely amount method requires the Company to determine the likelihood of earning the milestone payment. Given the high degree of uncertainty around achievement of these milestones, the Company determines the milestone amounts to be fully constrained and does not recognize revenue until the uncertainty associated with these payments is resolved. The Company will recognize revenue from sales-based royalty payments when or as the sales occur. The Company will re-evaluate the transaction price in each reporting period as uncertain events are resolved and other changes in circumstances occur. A performance obligation is a promise in a contract to transfer a distinct good or service to the collaborative partner and is the unit of account in Topic 606. A contract’s transaction price is allocated to each distinct performance obligation based on relative standalone selling price and recognized as revenue when, or as, the performance obligation is satisfied. Under Topic 606, the Company elected to use the practical expedients permitted related to adoption, which does not require the Company to disclose certain information regarding certain remaining performance obligations as of the end of the reporting period. Topic 606 is applicable for revenue recognized in accordance with the p See Note 2, “Collaboration Revenue” for specific details surrounding the Company’s collaboration arrangements.
Leases	Leases In February 2016, the FASB issued ASU 2016-02, Leases (Topic 842), which requires lessees to recognize most leases on the balance sheet as lease liabilities with corresponding right-of-use assets and to disclose key information about leasing arrangements. The Company adopted Topic 842 on its effective date in the first quarter of 2019 using a modified retrospective approach. The Company elected the available package of practical expedients upon adoption, which allowed it to carry forward historical assessment of whether existing agreements contained a lease and the classification of existing operating leases. The Company continues to report its financial position as of December 31, 2018 under the former lease accounting standard (Topic 840) in the condensed consolidated balance sheet The adoption impact was due to the recognition of an operating lease liability with a corresponding right-of-use asset based on the present value of remaining minimum lease payments. A reduction of the right-of-use asset was recorded to reflect the balance of the deferred rent obligation and there was no impact to retained earnings.
Research and Development, net	Research and Development, Net Research and development costs are expensed as incurred. 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.
Statement of Cash Flows	Statement of Cash Flows The following table provides a reconciliation of cash and cash equivalents and restricted cash reported within the condensed consolidated balance sheet to the total of the same such amounts shown in the condensed consolidated statement of cash flows: (in thousands) March 31, 2019 March 31, 2018 Cash and cash equivalents $ 31,220 $ 36,289 Non-current restricted cash 107 107 Total cash, cash equivalents and restricted cash shown in the statement of cash flows $ 31,327 $ 36,396
Net Loss per Share	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 treas ury-stock method. Dilutive ordinary shares are comprised of share options. No dividends were declared or paid during the reported periods.
Recently Adopted Accounting Pronouncements	Recently Adopted Accounting Pronouncements Revenue from Contracts with Customers In May 2014, the Financial Accounting Standards Board (FASB) issued Topic 606, which supersedes nearly all existing revenue recognition guidance under GAAP. The FASB subsequently issued amendments to Topic 606 that have the same effective date and transition date. The Company adopted this new guidance, effective January 1, 2019, using the modified retrospective transition method, in which the standard is applied as of the date of initial adoption. The Company recorded the cumulative effect of initially applying the standard as an adjustment to the opening balance of accumulated deficit. The adoption of the new revenue recognition guidance resulted in an increase of $0.8 million to deferred revenue and an increase of $0.8 million to accumulated deficit as of January 1, 2019. The change in revenue was due to a change in how the Company accounts for changes in the measure of progress and changes to the transaction price and for the recognition of revenue. Under Topic 605, the Company accounted for changes to the measure of progress and changes to the transaction price prospectively. Topic 606 requires companies to account for a change to the measure of progress or a change to the transaction price as a cumulative catch-up in the period of change. There were no other impacts upon the adoption of Topic 606. The Company will apply the standard to all new contracts initiated on or after the effective date. Under prior guidance, collaboration revenue recognized would have been $4.1 million for the three months ended March 31, 2019, which is $0.3 million lower than the amount recognized under current guidance. Leases In February 2016, the FASB issued Accounting Standards Update ("ASU") 2016-02, Leases (Topic 842) In July 2018, the FASB issued ASU 2018-11, Leases (Topic 842): Targeted Improvements provides entities an optional transition method to apply the new guidance as of the adoption date, rather than as of the earliest period presented. In transition, entities may also elect a package of practical expedients that must be applied in its entirety to all leases commencing before the effective date, unless the lease was modified, to not reassess (a) the existence of a lease, (b) lease classification or (c) determination of initial direct costs, which effectively allows entities to carryforward accounting conclusions under previous U.S. GAAP. The Company adopted ASU 2016-02, using the optional transition method and electing the package of practical expedients described above on January 1, 2019. Due to the adoption, the Company recognized a new lease liability on the Company's consolidated balance sheet for its operating lease of office and lab space of $6.2 million on January 1, 2019, with a corresponding right-of-use asset of $5.7 million based on the present value of the remaining minimum rental payments. See Note 11 for further discussion.

Description of Business, Basi_3

Description of Business, Basis of Presentation and Summary of Significant Accounting Policies (Tables)	3 Months Ended
	Mar. 31, 2019
Accounting Policies [Abstract]
Schedule of Cash and Cash Equivalents and Restricted Cash	The following table provides a reconciliation of cash and cash equivalents and restricted cash reported within the condensed consolidated balance sheet to the total of the same such amounts shown in the condensed consolidated statement of cash flows: (in thousands) March 31, 2019 March 31, 2018 Cash and cash equivalents $ 31,220 $ 36,289 Non-current restricted cash 107 107 Total cash, cash equivalents and restricted cash shown in the statement of cash flows $ 31,327 $ 36,396

Collaboration Revenue (Tables)

Collaboration Revenue (Tables)	3 Months Ended
	Mar. 31, 2019
Collaboration Agreements [Abstract]
Summary of Changes in Balances of Contract Assets and Contract Liability	The following table presents changes during the three months ended March 31, 2019 in the balances of contract assets, including receivables from collaborative partners, and contract liabilities, including deferred revenue, as compared to what was disclosed in the Company’s Annual Report. (in thousands) Contract Assets Balance at December 31, 2018 $ 4,480 Additions 3,611 Deductions (3,634 ) Balance at March 31, 2019 $ 4,457 (in thousands) Contract Liabilities Balance at December 31, 2018 $ 13,806 Additions for advanced billings 5,868 Additions for performance obligations to be satisfied in current and future periods in connection with Topic 606 adoption 803 Deductions for performance obligations satisfied in current period (4,724 ) Balance at March 31, 2019 $ 15,753

Balance Sheet Details (Tables)

Balance Sheet Details (Tables)	3 Months Ended
	Mar. 31, 2019
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 March 31, 2019 and December 31, 2018: (in thousands) March 31, 2019 December 31, 2018 Prepaid expenses $ 807 $ 546 Other current assets 122 92 Total $ 929 $ 638
Summary of Components of Property and Equipment	Property and equipment, net consisted of the following: (in thousands) March 31, 2019 December 31, 2018 Research equipment $ 2,854 $ 2,711 Computers and software 235 200 Office equipment and furniture 561 527 Leasehold improvements 35 34 Total 3,685 3,472 Less accumulated depreciation and amortization (1,669 ) (1,497 ) Property and equipment, net $ 2,016 $ 1,975
Schedule of Accrued Liabilities	Accrued liabilities consisted of the following as of March 31, 2019 and December 31, 2018: (in thousands) March 31, 2019 December 31, 2018 Accrued compensation $ 1,015 $ 974 Refundable fees received — 2,259 Current portion of operating lease liability 750 — Other accrued liabilities 1,001 674 Total $ 2,766 $ 3,907

Share-Based Compensation (Table

Share-Based Compensation (Tables)	3 Months Ended
	Mar. 31, 2019
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 Three Months Ended March 31, 2019 2018 Expected life (in years) 6.1 7.3 Expected volatility 74.1 % 76.4 % Expected dividend yield — % — % Risk-free interest rate 2.51 % 1.87 % Grant date weighted average fair value $ 3.19 $ 7.94
Summary of Share Option Activity	The following table summarizes the Company’s share option activity Number of Shares Weighted Average Exercise Price Weighted- Average Remaining Contractual Term (Years) Aggregate Intrinsic Value (in thousands) Outstanding - December 31, 2018 1,189,433 $ 7.41 Granted 76,000 * $ 4.80 Exercised — $ — $ — Forfeited/cancelled (38,500 ) $ 8.08 Outstanding - March 31, 2019 1,226,933 $ 6.95 9.02 $ 1,254 Exercisable - March 31, 2019 330,661 $ 6.14 7.60 $ 558 Exercisable and expected to vest - March 31, 2019 1,226,933 $ 6.95 9.02 $ 1,254 * Total options granted during the first quarter of 2019 exclude 160,000 options granted to the Chief Executive Officer and Chief Financial Officer which remain subject to shareholder approval.
Schedule of Share-based Compensation Expenses	Share-based compensation expenses included in the Company’s condensed statements of operations and comprehensive loss for the three months ended March 31, 2019 and 2018 were: For the Three Months Ended March 31, (in thousands) 2019 2018 Research and development $ 152 $ 8 General and administrative 247 18 Total $ 399 $ 26

Leases (Tables)

Leases (Tables)	3 Months Ended
	Mar. 31, 2019
Leases [Abstract]
Payments of Operating Lease Liability	As of March 31, 2019, the payments of the operating lease liability were as follows: (in thousands) Remaining Lease Payments 2019 $ 932 2020 1,272 2021 1,310 2022 1,349 2023 1,390 Thereafter 1,745 Total remaining lease payments 7,998 Less: imputed interest (1,765 ) Total operating lease liability $ 6,233 Less: current portion of operating lease liability (750 ) Operating lease liability, net of current portion 5,483 Weighted-average remaining lease term 6 years Weighted-average discount rate 8.4 %

Description of Business, Basi_4

Description of Business, Basis of Presentation and Summary of Significant Accounting Policies (Details Textual)	Jan. 01, 2019USD ($)	Oct. 12, 2018USD ($)	Mar. 31, 2019USD ($)Segment	Feb. 08, 2019shares	Dec. 31, 2018USD ($)	Oct. 15, 2018USD ($)
Summary Of Significant Accounting Policy [Line Items]
Accumulated deficit			$ (52,561,000)		$ (44,874,000)
Number of ordinary share of Newco in exchange for each ordinary share | shares				1
Number of operating segment for research and developement | Segment			1
Operating lease liability			$ 6,233,000
Operating lease right-of-use asset			5,690,000
Office and Lab Space [Member]
Summary Of Significant Accounting Policy [Line Items]
Operating lease liability	$ 6,200,000
Operating lease right-of-use asset	5,700,000
Calculated under Revenue Guidance in Effect before Topic 606 [Member]
Summary Of Significant Accounting Policy [Line Items]
Collabration revenue			4,100,000
Difference between Revenue Guidance in Effect before and after Topic 606 [Member]
Summary Of Significant Accounting Policy [Line Items]
Collabration revenue			$ 300,000
ASC 606 [Member]
Summary Of Significant Accounting Policy [Line Items]
Increase in deferred revenue due to adoption of new revenue recogition	800,000
Increase in accumulated deficit	$ 800,000
Loan and Security Agreement [Member] | Western Alliance Bank [Member] | Term Loan [Member]
Summary Of Significant Accounting Policy [Line Items]
Gross proceeds from long-term debt agreement		$ 10,000,000
Sales Agreement [Member] | Leerink Partners LLC [Member] | Maximum [Member]
Summary Of Significant Accounting Policy [Line Items]
Aggregate amount of ordinary shares sold						$ 30,000,000

Schedule of Cash and Cash Equiv

Schedule of Cash and Cash Equivalents and Restricted Cash (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018	Mar. 31, 2018	Dec. 31, 2017
Accounting Policies [Abstract]
Cash and cash equivalents	$ 31,220	$ 36,709	$ 36,289
Non-current restricted cash	107	107	107
Total cash, cash equivalents and restricted cash shown in the statement of cash flows	$ 31,327	$ 36,816	$ 36,396	$ 25,238

Collaboration Revenue - Summary

Collaboration Revenue - Summary of Changes in Balances of Contract Assets and Contract Liability (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2019USD ($)
Collaboration Agreements [Abstract]
Contract Assets, Balance	$ 4,480
Contract Assets, Additions	3,611
Contract Assets, Deductions	(3,634)
Contract Assets, Balance	4,457
Contract Liabilities, Balance	13,806
Contract Liabilities, Additions for advanced billings	5,868
Contract Liabilities, Additions for performance obligations to be satisfied in current and future periods in connection with Topic 606 adoption	803
Contract Liabilities, Deductions for performance obligations satisfied in current period	(4,724)
Contract Liabilities, Balance	$ 15,753

Collaboration Revenue (Details

Collaboration Revenue (Details Textual)	Feb. 11, 2019	Jan. 01, 2019USD ($)	Mar. 31, 2019USD ($)Performance	Dec. 31, 2018USD ($)	Mar. 31, 2018USD ($)	Dec. 31, 2017USD ($)
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Deferred revenue			$ 15,753,000	$ 13,806,000
Collaboration revenue			4,350,000		$ 2,367,000
ASC 606 [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Increase in deferred revenue due to adoption of new revenue recogition		$ 800,000
Research Collaboration And Exclusive License Agreement [Member] | Collaboration Partner Janssen [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Upfront payment received			7,700,000
Revenue recognition potential milestone revenue recognized			56,500,000
Research Collaboration And Exclusive License Agreement [Member] | Collaboration Partner Janssen [Member] | ASC 606 [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Upfront payment received			7,700,000
Reimbursable out-of-pocket costs			18,200,000
Remaining performance obligation			0
Adjustments to transaction price			$ 0
Number of performance obligation | Performance			1
Deferred revenue			$ 6,300,000	6,500,000
Collaboration revenue			500,000		100,000
Research Collaboration And Exclusive License Agreement [Member] | Collaboration Partner - Ultragenyx [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Revenue recognition potential milestone revenue recognized			139,000,000
Upfront fee received			$ 10,000,000
Revenue recognition, milestone			Ultragenyx 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.
Royalty payment term description			Ultragenyx will pay royalties as a single-digit percentage of net sales on a product-by-product and country-by-country basis during the applicable royalty term.
Revenue recognized as one time payment						$ 2,000,000
Annual maintenance fee				1,500,000
Research Collaboration And Exclusive License Agreement [Member] | Collaboration Partner - Ultragenyx [Member] | ASC 606 [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Remaining performance obligation			$ 0
Adjustments to transaction price			$ 0
Number of performance obligation | Performance			1
Deferred revenue			$ 2,400,000	$ 2,700,000
Collaboration revenue			$ 1,400,000		1,500,000
Revenue, practical expedient description			Therefore under the practical expedient the Company is not required to determine the transaction price, allocate the transaction price and determine the timing of revenue recognition for the reimbursement of labor and expenses. None of the development and commercialization milestones were included in the transaction price, as all milestone amounts were fully constrained.
Estimated period to recognize up front payment as revenue			47 months
Cumulative catch-up amount added to transaction price upon amendment			$ 2,000,000
Increase in deferred revenue due to adoption of new revenue recogition			800,000
Decrease in retained earnings due to adoption of new revenue recognition			$ 800,000
mRNA Technology [Member] | Collaboration Partner - CureVac [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Royalty payment term description			CureVac will pay royalties as a percentage of net sales on a product-by-product and country-by-country basis during the applicable royalty term in the low single-digit range
Development and option agreement date			Jan. 31, 2018
Expiration of initial term			8 years
Option to extend intial term on an annual basis			3 years
mRNA Technology [Member] | Collaboration Partner - CureVac [Member] | Rare Disease Targets [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Revenue recognition potential milestone revenue recognized			$ 14,000,000
mRNA Technology [Member] | Collaboration Partner - CureVac [Member] | Non-Rare Disease Targets [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Revenue recognition potential milestone revenue recognized			23,000,000
mRNA Technology [Member] | Collaboration Partner - CureVac [Member] | ASC 606 [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Remaining performance obligation			0
Adjustments to transaction price			$ 0
Number of performance obligation | Performance			1
Deferred revenue			$ 4,200,000		4,400,000
Collaboration revenue			1,900,000		$ 200,000
Upfront fee received			$ 5,000,000
Revenue, practical expedient description			Therefore under the practical expedient the Company is not required to determine the transaction price, allocate the transaction price and determine the timing of revenue recognition for the reimbursement of labor and expenses. None of the development and commercialization milestones were included in the transaction price, as all milestone amounts were fully constrained.
mRNA Technology [Member] | Collaboration Partner Cure Vac Entered Into Co Development Agreement
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Collaboration agreement termination date	Feb. 11, 2019
Percentage of global rights reassumed	100.00%
Minimum [Member] | Research Collaboration And Exclusive License Agreement [Member] | Collaboration Partner Janssen [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Option exercise revenue range per target						1,000,000
Maximum [Member] | Research Collaboration And Exclusive License Agreement [Member] | Collaboration Partner Janssen [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Option exercise revenue range per target						$ 5,000,000

Collaboration Revenue (Detail_2

Collaboration Revenue (Details Textual 1) - Research Collaboration And Exclusive License Agreement [Member] - Collaboration Partner Janssen [Member] - ASC 606 [Member] $ in Millions	Mar. 31, 2019USD ($)
Revenue Remaining Performance Obligation Expected Timing Of Satisfaction [Line Items]
Remaining performance obligation	$ 0
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date: 2019-04-01
Revenue Remaining Performance Obligation Expected Timing Of Satisfaction [Line Items]
Remaining research period	12 months
Remaining performance obligation	$ 24.2

Balance Sheet Details - Schedul

Balance Sheet Details - Schedule of Prepaid Expenses and Other Current Assets (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Prepaid Expenses And Other Current Assets [Abstract]
Prepaid expenses	$ 807	$ 546
Other current assets	122	92
Total	$ 929	$ 638

Balance Sheet Details - Summary

Balance Sheet Details - Summary of Components of Property and Equipment, Net (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Property Plant And Equipment [Line Items]
Property and equipment, gross	$ 3,685	$ 3,472
Less accumulated depreciation and amortization	(1,669)	(1,497)
Property and equipment, net	2,016	1,975
Research equipment [Member]
Property Plant And Equipment [Line Items]
Property and equipment, gross	2,854	2,711
Computer and software [Member]
Property Plant And Equipment [Line Items]
Property and equipment, gross	235	200
Office equipment and furniture [Member]
Property Plant And Equipment [Line Items]
Property and equipment, gross	561	527
Leasehold improvements [Member]
Property Plant And Equipment [Line Items]
Property and equipment, gross	$ 35	$ 34

Balance Sheet Details (Details

Balance Sheet Details (Details Textual) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Balance Sheet Related Disclosures [Abstract]
Depreciation and amortization	$ 172	$ 111

Balance Sheet Details - Sched_2

Balance Sheet Details - Schedule of Accrued Liabilities (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Accrued Liabilities Current [Abstract]
Accrued compensation	$ 1,015	$ 974
Refundable fees received		2,259
Current portion of operating lease liability	750
Other accrued liabilities	1,001	674
Total	$ 2,766	$ 3,907

Debt (Details Textual)

Debt (Details Textual) - Loan and Security Agreement [Member] - Western Alliance Bank [Member] - Long-term Debt [Member] - USD ($)	Oct. 12, 2018	Mar. 31, 2019
Debt Instrument [Line Items]
Gross proceeds from long-term debt agreement	$ 10,000,000
Loan maturity date	Oct. 1, 2022
Interest of the prime rate plus	1.25%
Loan interest payment terms		The loan has an interest-only period of 19 months, which could be extended by an additional 6 months if certain conditions are met, followed by an amortization period of 30 months, or 24 months if the interest-only period is extended.
Loan interest-only payment period	19 months
Loan interest-only payment period	6 months
Debt Instrument, amortization period	30 months
Debt Instrument, amortization period	24 months
Loan orgination fee paid	$ 128,000
Warrant fee payable	$ 350,000
Prepayment fee percentage	3.00%
Prepayment fee percentage	2.00%
Percentage of fee liable on principal balance	3.00%
Fee payable upon repayment	$ 300,000
Debt instrument, collateral		The Loan is collateralized by all of the assets of the Company, excluding intellectual property, which is subject to a negative pledge. The Loan contains customary conditions of borrowing, events of default and covenants, including covenants that restrict the Company’s ability to dispose of assets, merge with or acquire other entities, incur indebtedness and make distributions to holders of the Company’s capital stock. In addition, the Company is required to maintain at least 50% of its deposit and investment accounts, or $20 million, whichever is lower, with the Western Alliance Bank.
Debt instrument, collateral amount	20,000,000
Available sale of equity securities	$ 15,000,000
Minimum [Member]
Debt Instrument [Line Items]
Percentage required to be maintain in deposit and investment	50.00%

Shareholders' Equity (Details T

Shareholders' Equity (Details Textual)	1 Months Ended	3 Months Ended		12 Months Ended
	Mar. 31, 2013$ / sharesshares	Mar. 31, 2019shares	Mar. 31, 2018shares	Dec. 31, 2017USD ($)Milestoneshares	Dec. 31, 2018shares	Dec. 31, 2016Milestone	Dec. 31, 2014shares
Class Of Stock [Line Items]
Antidilutive securities excluded from computation of earnings per share		67,051	110,883
Treasury shares		43,000	43,000		43,000
Unvested Restricted Ordinary Shares [Member]
Class Of Stock [Line Items]
Antidilutive securities excluded from computation of earnings per share		622,667	622,667
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		622,667,000			622,667,000		769,176,000
Accelerated ordinary shares vested				146,510,000
Modification expense resulting from accelerated vesting of ordinary shares | $				$ 1,495,000
Vested After Obtaining Suitable siRNA License [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%

Share-Based Compensation (Detai

Share-Based Compensation (Details Textual) $ in Millions	1 Months Ended	3 Months Ended
	Feb. 28, 2019shares	Mar. 31, 2019USD ($)shares	Aug. 31, 2018shares
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Reverse share split, description		1- for- 7
Reverse split of ordinary shares, ratio		0.1429
Compensation cost not yet recognized | $		$ 4.6
Weighted-average remaining service period		3 years 1 month 6 days
Fair value of options vested | $		$ 0.3
2013 Equity Incentive Plan [Member] | Stock Option [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		38,751
Shares issued in period		0
2010 Equity Incentive Plan [Member] | Stock Option [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share options expiration period		10 years
Common stock reserved for future issuance		111,251
2018 Omnibus Equity Incentive Plan [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares authorized for grant			1,100,000
Common stock reserved for future issuance		255,250
Shares issued in period	403,750
2018 Omnibus Equity Incentive Plan [Member] | Chief Executive Officer And Chief Financial Officer [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares issued in period	160,000
2018 Omnibus Equity Incentive Plan [Member] | Non-Executive Officer [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares issued in period	130,000

Share-Based Compensation (Det_2

Share-Based Compensation (Details) - $ / shares	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Grant date weighted average fair value	$ 3.19	$ 7.94
Stock Options [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected life (in years)	6 years 1 month 6 days	7 years 3 months 18 days
Expected volatility	74.10%	76.40%
Risk-free interest rate	2.51%	1.87%

Share-Based Compensation (Det_3

Share-Based Compensation (Details 1) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2019USD ($)$ / sharesshares
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Number of Shares, Outstanding | shares	1,189,433
Number of Shares, Granted | shares	76,000
Number of Shares, Forfeited/cancelled | shares	(38,500)
Number of Shares, Outstanding | shares	1,226,933
Number of Shares, Exercisable – March 31, 2019 | shares	330,661
Number of Shares, Exercisable and expected to vest – March 31, 2019 | shares	1,226,933
Weighted-Average Exercise Price, Outstanding | $ / shares	$ 7.41
Weighted-Average Exercise Price, Granted | $ / shares	4.80
Weighted-Average Exercise Price, Forfeited/cancelled | $ / shares	8.08
Weighted-Average Exercise Price, Outstanding - March 31, 2019 | $ / shares	6.95
Weighted-Average Exercise Price, Exercisable - March 31, 2019 | $ / shares	6.14
Weighted-Average Exercise Price, Exercisable and expected to vest - March 31, 2019 | $ / shares	$ 6.95
Weighted-Average Remaining Contractual Term (Years), Outstanding - March 31, 2019	9 years 7 days
Weighted-Average Remaining Contractual Term (Years), Exercisable - March 31, 2019	7 years 7 months 6 days
Weighted-Average Remaining Contractual Term (Years), Exercisable and expected to vest – March 31, 2019	9 years 7 days
Aggregate Intrinsic Value, Outstanding – March 31, 2019 | $	$ 1,254
Aggregate Intrinsic Value, Exercisable – March 31, 2019 | $	558
Aggregate Intrinsic Value, Exercisable and expected to vest – March 31, 2019 | $	$ 1,254

Share-Based Compensation (Det_4

Share-Based Compensation (Details 1) (Parenthetical)	3 Months Ended
	Mar. 31, 2019shares
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Options granted	76,000
Chief Executive Officer And Chief Financial Officer [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Options granted	160,000

Share-Based Compensation (Det_5

Share-Based Compensation (Details 2) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share-based compensation expenses	$ 399	$ 26
Research and Development [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share-based compensation expenses	152	8
General and Administrative [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share-based compensation expenses	$ 247	$ 18

Leases (Details Textual)

Leases (Details Textual) - USD ($)	1 Months Ended	3 Months Ended
	Oct. 31, 2017	Mar. 31, 2019
Lessee Lease Description [Line Items]
Operating lease, remaining lease term		6 years
Operating lease costs		$ 300,000
October 2017 Lease Amendment [Member]
Lessee Lease Description [Line Items]
Operating lease extended additional term	84 months
Operating lease, remaining lease term	6 years
Lessee, operating lease, term of contract	4 months
Tenant improvement allowance	$ 74,000
Lessee, operating leases, option to extend	The lease may be extended for one five-year period at then current market rate with annual escalations;
Security	$ 96,000

Leases - Payments of Operating

Leases - Payments of Operating Lease Liability (Details) $ in Thousands	Mar. 31, 2019USD ($)
Leases [Abstract]
2019	$ 932
2020	1,272
2021	1,310
2022	1,349
2023	1,390
Thereafter	1,745
Total remaining lease payments	7,998
Less: imputed interest	(1,765)
Total operating lease liability	6,233
Less: current portion of operating lease liability	(750)
Operating lease liability, net of current portion	$ 5,483
Weighted-average remaining lease term	6 years
Weighted-average discount rate	8.40%

Related Party Transactions - Pr

Related Party Transactions - Providence (Details Textual) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Related Party Transaction [Line Items]
Revenue	$ 4,350	$ 2,367
Providence Therapeutics, Inc [Member] | Research Collaboration and License Agreement [Member]
Related Party Transaction [Line Items]
Revenue	$ 300	$ 300

Related Party Transactions - Eq

Related Party Transactions - Equity-Method Investment (Details Textual) - USD ($)	3 Months Ended
	Mar. 31, 2019	Dec. 31, 2018	Jun. 30, 2018
Related Party Transaction [Line Items]
Share of losses for investee	$ 288,000
Equity investments		$ 288,000
ADAIR Technology [Member]
Related Party Transaction [Line Items]
Equity method ownership percentage			30.00%
Share of losses for investee	600,000
Equity investments	$ 0
ADAIR Technology [Member] | Minimum [Member]
Related Party Transaction [Line Items]
Equity method ownership percentage			20.00%