Arcturus Therapeutics (ARCT) 10-Q 14 Aug 19 2019 Q2 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	6 Months Ended
	Jun. 30, 2019	Aug. 09, 2019
Document And Entity Information [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Jun. 30, 2019
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	Q2
Trading Symbol	ARCT
Entity Registrant Name	Arcturus Therapeutics Holdings Inc.
Entity Central Index Key	0001768224
Entity Current Reporting Status	Yes
Current Fiscal Year End Date	--12-31
Entity Filer Category	Non-accelerated Filer
Entity Small Business	true
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity File Number	001-38942
Entity Tax Identification Number	320595345
Entity Address, Address Line One	10628 Science Center Drive
Entity Address, Address Line Two	Suite 250
Entity Address, City or Town	San Diego
Entity Address, State or Province	California
Entity Address, Postal Zip Code	92121
City Area Code	858
Local Phone Number	900-2660
Entity Common Stock, Shares Outstanding		14,274,378

CONDENSED CONSOLIDATED BALANCE

CONDENSED CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Current assets:
Cash and cash equivalents	$ 55,840	$ 36,709
Accounts receivable	5,817	4,481
Prepaid expenses and other current assets	1,681	638
Total current assets	63,338	41,828
Property and equipment, net	1,986	1,975
Operating lease right-of-use asset, net	5,509
Equity-method investment		288
Non-current restricted cash	107	107
Total assets	70,940	44,198
Current liabilities:
Accounts payable	3,187	2,398
Accrued liabilities	3,497	3,907
Deferred revenue	9,730	6,272
Total current liabilities	16,414	12,577
Deferred revenue, net of current portion	17,652	7,534
Long-term debt	9,980	9,911
Operating lease liability, net of current portion	5,276
Deferred rent		534
Total liabilities	49,322	30,556
Stockholders' equity
Common stock: $0.001 par value; 30,000 shares authorized; 13,120 issued and outstanding at June 30, 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	13	214
Additional paid-in capital	74,851	58,302
Accumulated deficit	(53,246)	(44,874)
Total stockholders' equity	21,618	13,642
Total liabilities and stockholders' equity	$ 70,940	$ 44,198

CONDENSED CONSOLIDATED BALANC_2

CONDENSED CONSOLIDATED BALANCE SHEETS (Parenthetical)	Jun. 30, 2019$ / sharesshares	Dec. 31, 2018₪ / sharesshares
Statement Of Financial Position [Abstract]
Common stock, par value | (per share)	$ 0.001	₪ 0.07
Common stock, shares authorized	30,000,000	30,000,000
Treasury shares		43,000
Common stock, shares issued	13,120,000	10,762,000
Common stock, shares outstanding	13,120,000	10,719,000

CONDENSED CONSOLIDATED STATEMEN

CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE LOSS - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Statement Of Income And Comprehensive Income [Abstract]
Collaboration revenue	$ 10,153	$ 2,386	$ 14,503	$ 4,753
Operating expenses:
Research and development, net	7,269	4,225	14,593	8,166
General and administrative	3,456	8,233	6,990	13,331
Total operating expenses	10,725	12,458	21,583	21,497
Loss from operations	(572)	(10,072)	(7,080)	(16,744)
Loss from equity-method investment		(47)	(288)	(47)
Finance (expense) income, net	(113)	169	(201)	270
Net loss	$ (685)	$ (9,950)	$ (7,569)	$ (16,521)
Net loss per share, basic and diluted	$ (0.07)	$ (0.99)	$ (0.74)	$ (1.65)
Weighted-average shares outstanding, basic and diluted	10,412	10,057	10,255	10,043
Comprehensive loss:
Net loss	$ (685)	$ (9,950)	$ (7,569)	$ (16,521)
Unrealized gain on short-term investments		7		5
Comprehensive loss	$ (685)	$ (9,943)	$ (7,569)	$ (16,516)

CONDENSED CONSOLIDATED STATEM_2

CONDENSED CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY - USD ($) $ in Thousands	Total	Common Stock [Member]	Additional Paid-In Capital [Member]	Accumulated Other Comprehensive (Loss) Gain [Member]	Accumulated Deficit [Member]
Balance at Dec. 31, 2017	$ 33,794	$ 212	$ 56,674	$ (3)	$ (23,089)
Balance (in shares) at Dec. 31, 2017		10,699,000
Net loss	(16,521)				(16,521)
Unrealized gain on short-term investments	5			5
Issuance of common stock upon exercise of stock options	351	$ 2	349
Issuance of common stock upon exercise of stock option (in shares)		49,000
Share-based compensation	166		166
Balance at Jun. 30, 2018	17,795	$ 214	57,189	2	(39,610)
Balance (in shares) at Jun. 30, 2018		10,748,000
Balance at Mar. 31, 2018	27,551	$ 213	57,003	(5)	(29,660)
Balance (in shares) at Mar. 31, 2018		10,738,000
Net loss	(9,950)				(9,950)
Unrealized gain on short-term investments	7			7
Issuance of common stock upon exercise of stock options	47	$ 1	46
Issuance of common stock upon exercise of stock option (in shares)		10,000
Share-based compensation	140		140
Balance at Jun. 30, 2018	17,795	$ 214	57,189	$ 2	(39,610)
Balance (in shares) at Jun. 30, 2018		10,748,000
Balance at Dec. 31, 2018	13,642	$ 214	58,302		(44,874)
Balance (in shares) at Dec. 31, 2018		10,762,000
Net loss	(7,569)				(7,569)
Treasury stock		(43,000)
Issuance of common stock upon exercise of stock options	$ 1		1
Issuance of common stock upon exercise of stock option (in shares)	823	1,000
Share-based compensation	$ 802		802
Redomiciliation share exchange		$ (203)	203
Issuance of restricted common stock and option, net of issuance costs	15,545	$ 2	15,543
Issuance of restricted common stock and option, net of issuance costs (in shares)		2,400,000
Effect of adoption of ASU 2014-09	(803)				(803)
Balance at Jun. 30, 2019	21,618	$ 13	74,851		(53,246)
Balance (in shares) at Jun. 30, 2019		13,120,000
Balance at Mar. 31, 2019	6,354	$ 214	58,701		(52,561)
Balance (in shares) at Mar. 31, 2019		10,762,000
Net loss	(685)				(685)
Treasury stock		(43,000)
Issuance of common stock upon exercise of stock options	1		1
Issuance of common stock upon exercise of stock option (in shares)		1,000
Share-based compensation	403		403
Redomiciliation share exchange		$ (203)	203
Issuance of restricted common stock and option, net of issuance costs	15,545	$ 2	15,543
Issuance of restricted common stock and option, net of issuance costs (in shares)		2,400,000
Balance at Jun. 30, 2019	$ 21,618	$ 13	$ 74,851		$ (53,246)
Balance (in shares) at Jun. 30, 2019		13,120,000

CONDENSED CONSOLIDATED STATEM_3

CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018
OPERATING ACTIVITIES:
Net loss	$ (7,569)	$ (16,521)
Adjustments to reconcile net loss to net cash provided by (used in) operating activities:
Depreciation and amortization	349	256
Amortization of right-of-use operating lease asset	359
Share-based compensation expense	802	166
Non-cash interest expense	69
Loss from equity-method investment	288	47
Changes in operating assets and liabilities
Accounts receivable	(1,336)	(891)
Prepaid expense and other assets	(1,043)	644
Accounts payable	773	838
Accrued liabilities	(1,536)	1,764
Deferred revenue	12,773	5,542
Net cash provided by (used in) operating activities	3,929	(8,202)
INVESTING ACTIVITIES:
Proceeds from maturities of short-term investments		22,253
Purchases of short-term investments		(9,211)
Acquisition of property and equipment	(344)	(1,000)
Net cash (used in) provided by investing activities	(344)	12,042
FINANCING ACTIVITIES:
Proceeds from the issuance of restricted common stock and option, net of issuance costs	15,545
Proceeds from exercise of stock options	1	351
Net cash provided by financing activities	15,546	351
NET INCREASE IN CASH, CASH EQUIVALENTS AND RESTRICTED CASH	19,131	4,191
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	55,947	29,429
Supplemental disclosure of cash flow information
Cash paid for interest	340
Non-cash investing activities
Right-of-use asset obtained in exchange for lease liabilities	5,868
Sale of intangible assets for equity investment		590
Release of repurchase liability for restricted shares		37
Purchase of property and equipment in accounts payable	$ 16	$ 150

Description of Business, Basis

Description of Business, Basis of Presentation and Summary of Significant Accounting Policies	6 Months Ended
	Jun. 30, 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 Holdings Inc. and its subsidiaries (referred to as the “Company”) is a RNA medicines company focused on significant opportunities in rare, liver, and respiratory diseases. Management believes that 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. The financial statements for periods prior to June 17, 2019 Arcturus Therapeutics Ltd. June 17, 2019 Arcturus Therapeutics Ltd Basis of Presentation The accompanying condensed consolidated financial statements include the accounts of Arcturus Therapeutics Holdings Inc. 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, 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 Liquidity 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 June 18, 2019, the Company entered into a Third Amendment to the Research Collaboration and License Agreement (the “Third Amendment”) with Ultragenyx Pharmaceutical Inc. (“Ultragenyx”), from which the Company received $30.0 million (Note 2). 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 June 30, 2019 has an accumulated deficit of $53.2 million. Recent Developments Arcturus Therapeutics Ltd. (“Arcturus Israel”) completed the process to redomicile from an Israeli limited company to a Delaware corporation (the “Redomiciliation”). On February 11, 2019, Arcturus Israel filed an application with the Tel-Aviv District Court (the “Israeli Court”) to approve the convening of a general shareholders meeting of Arcturus Israel 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 Securities and Exchange Commission 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, held on May 17, 2019, as described in the Form S-4. The general shareholders meeting resulted in the approval of the Redomiciliation, and Arcturus Israel then approached the Israeli Court and requested its approval of the Redomiciliation. In connection with the Redomiciliation, Arcturus Israel entered into a share exchange agreement (the “Exchange Agreement”) with a special-purpose company, Arcturus Therapeutics Holdings Inc., the reporting company and parent to Arcturus Therapeutics, Inc. (“Arcturus Sub”). In furtherance of the Redomiciliation, and pursuant to the terms of the Exchange Agreement, the holders of ordinary shares of Arcturus Israel as of a future record date and the holders of options to purchase ordinary shares of Arcturus Israel as of the same record date transferred their ordinary shares of Arcturus Israel and options to purchase ordinary shares of Arcturus Israel, respectively, to the Company and, in exchange thereof, received one share of common stock of the Company for each ordinary share of Arcturus Israel and an option to purchase one share of common stock of the Company in exchange for each ordinary share of Arcturus Israel underlying the existing option to be so exchanged, respectively. As a result of the Exchange Agreement, the par value of Arcturus Israel’s ordinary shares prior to the Redomiciliation is presented in New Israeli Shekel (“NIS”) and the par value of the Company’s common stock subsequent to the Redomiciliation is presented in United States Dollars (“USD”). As of June 17, 2019, the common stock of the Company is listed on the NASDAQ Stock Market LLC (“NASDAQ”). Upon consummation of the transactions contemplated by the Share Exchange Agreement, Arcturus Israel’s ordinary shares were delisted from trading on NASDAQ, and Arcturus Israel became a private company (as defined in the Companies Law) wholly-owned by the Company. Pursuant to the Exchange Agreement, on June 12, 2019 all of the shares of Arcturus Sub were distributed to the Company and Arcturus Sub become a wholly-owned and direct subsidiary of the Company. This distribution was completed in connection with a liquidation of Arcturus Israel which was formally initiated after the redomiciliation described above. See “Note 10. Subsequent Events” 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 upfront 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 performs 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 assessments 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, preclinical studies 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) June 30, 2019 June 30, 2018 Cash and cash equivalents $ 55,840 $ 29,322 Non-current restricted cash 107 107 Total cash, cash equivalents and restricted cash shown in the statement of cash flows $ 55,947 $ 29,429 Net Loss per Share Basic net loss per share is calculated by dividing the net loss by the weighted-average number of shares of common stock outstanding for the period, without consideration for common stock equivalents. Diluted net loss per share is calculated by dividing the net loss by the weighted-average number of shares of common stock and dilutive common stock equivalents outstanding for the period determined using the treas ury-stock method. Dilutive shares of common stock are comprised of stock 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. 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 $6.4 million on January 1, 2019, with a corresponding right-of-use asset of $5.9 million based on the present value of the remaining minimum rental payments. See Note 8 for further discussion.

Collaboration Revenue

Collaboration Revenue	6 Months Ended
	Jun. 30, 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 six months ended June 30, 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 - December 31, 2018 $ 4,480 Additions for advanced billings 11,038 Deductions for cash collections (9,701 ) BALANCE – June 30, 2019 $ 5,817 (in thousands) Contract Liabilities BALANCE - December 31, 2018 $ 13,806 Additions for advanced billings 27,650 Additions for promised goods/services to be provided in current and future periods in connection with Topic 606 adoption 803 Deductions for promised goods/services provided in current period (14,877 ) BALANCE – June 30, 2019 $ 27,382 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 promised goods/services 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 promised goods/services are incapable of being distinct 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 promised goods/services, 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 June 30, 2019, the remaining transaction price of $23.6 million is expected to be recognized using an input method over the remaining research period of 21 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 June 30, 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 June 30, 2019 and December 31, 2018 for Janssen was $6.2 million and $6.5 million, respectively. The Company recognized revenue of $0.6 million and $1.1 million for the three and six months ended June 30, 2019, respectively, and $0.2 million and $0.3 million for the three and six months ended June 30, 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 granted to Ultragenyx a co-exclusive license under Arcturus technology and shall be in effect only during the reserve target exclusivity term as discussed 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 from $2.0 million to $5.0 million. Upon execution of Amendment 3, defined and discussed below, the option exercise fees per development target range from $0.5 million to $1.5 million. The agreement includes potential milestone payments for selected targets from Ultragenyx to the Company. The current potential development, regulatory and commercial milestone payments for the existing development targets as of June 30, 2019 are $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 June 30, 2019, the Company has not yet reached the clinical phase of the contract. In 2018, the Company signed an amendment with Ultragenyx, that will reduce option exercise fees, milestone payments and/or royalty rates by 50% dependent on whether a development target or product is not covered by a patent directed to a chemistry methodology to increase mRNA half-life. For Amendment 3, defined and discussed below, the 50% reduction does not apply to the option exercise fees. 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. On June 18, 2019, Arcturus and Ultragenyx amended the collaboration agreement for a third time (“Amendment 3”). As part of Amendment 3, the total number of targets was increased from 10 to 12, and reserve targets will be exclusively reserved for Ultragenyx with no fees for four years after execution of the amendment. An equity component was also added as part of Amendment 3 wherein Ultragenyx purchased 2.4 million shares of common stock at a premium price giving Ultragenyx 18.3% ownership in the Company. Along with the equity purchase, Ultragenyx received the option to purchase 0.6 million additional shares of common stock at $16 per share within two years of executing the amendment (Note 6). The consideration received from Ultragenyx is equal to $30.0 million, comprised of a $24.0 million common stock purchase and a $6.0 million upfront payment. Specifically for Amendment 3, management determined the transaction price to be $14.4 million, comprised of $6.0 million from the upfront payment and $8.4 million from the premium paid by Ultragenyx for the purchase of Arcturus common stock. See further discussion below regarding determining the transaction price. Management determined the fair value of the premium received by using the opening stock price subsequent to execution of Amendment 3 and applying a lack of marketability discount as the shares received by Ultragenyx are restricted for two years. 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 promised goods/services as of the inception of the Agreement and execution of Amendment 3: (i) research services, (ii) license to use Arcturus technology, (iii) exclusivity and (iv) participation in the Joint Steering Committee. The Company concluded that the promised goods/services are incapable of being distinct 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 as they are constrained, provided that the reported sales are reliably measurable and the Company has no remaining promised goods/services, as such sales were determined to relate predominantly to the license granted to Ultragenyx and therefore have also been excluded from the transaction price. Upon execution of the 2017 amendment, the $2.0 million payment was added to the transaction price. The exclusivity extension fee received by the Company during the fourth quarter of 2018 was recorded as deferred revenue and has been recognized as revenue on a straight-line basis over the one-year period that the promised goods/services are provided. Upon execution of Amendment 3, the exclusivity extension fee was added to the transaction price. Upon execution of Amendment 3, the Company concluded that there is a single performance obligation, and no allocation of the transaction price is necessary. Amendment 3 was deemed a contract modification and accounted for as part of the original Ultragenyx Agreement. Management increased the transaction price by $14.4 million and the Company recorded a cumulative catch-up adjustment of $1.1 million on the modification date. The new transaction price will be recognized to revenue on a straight-line basis using an input method over the 4-year reserve target exclusivity period. The reserve target exclusivity period represents the timing over which promised goods/services 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 period over which revenue is recognized as well as accounting for adjustments to the transaction price. 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 June 30, 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 June 30, 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”) which the Company considered a combined contract with the Development and Option Agreement for purposes of revenue recognition. 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. Subsequent to June 30, 2019, CureVac and the Company terminated the Co-Development Agreement for a settlement payment of $4.0 million (Note 10). 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. 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 promised goods/services 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 promised goods/services are incapable of being distinct 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 as they are constrained, provided that the reported sales are reliably measurable and the Company has no remaining promised goods/services, as such sales were determined to relate predominantly to the license granted to CureVac 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 June 30, 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 $5.0 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 using an input method over the eight-year contractual term as of June 30, 2019. Total deferred revenue as of June 30, 2019 and December 31, 2018 for CureVac was $4.0 million and $4.4 million, respectively. The Company recognized revenue of $3.4 million and $5.3 million for the three and six months ended June 30, 2019, respectively, and $0.3 million and $0.5 million for the three and six months ended June 30, 2018, respectively. No adjustment was necessary upon adoption of Topic 606 Other Collaboration Revenue The Company recognized total other collaboration revenue of $3.6 million and $4.1 million for the three and six months ended June 30, 2019, respectively, and $0.7 million and $1.2 million for the three and six months ended June 30, 2018, respectively. Of the total other collaboration revenue for the three and six months ended June 30, 2019, $3.3 million and $3.5 million, respectively, was primarily related to the Research and Exclusive License Agreement with Synthetic Genomics, Inc. (“SGI”) into which the Company entered during October 2017. Under the agreement, the Company granted SGI an exclusive license for the Arcturus LMD Technology to research, develop and sell products for diseases excluding all respiratory disease viruses other than influenza. Revenue related to this agreement is made up of labor reimbursements and sublicense revenue. The Company recognized a sublicense revenue amount of $3.3 million for the three months ended June 30, 2019 whereby SGI sublicensed to multiple parties.

Fair Value Measurements

Fair Value Measurements	6 Months Ended
	Jun. 30, 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 June 30, 2019 and December 31, 2018, all assets measured at fair value on a recurring basis consisted of cash equivalents, money market funds, 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	6 Months Ended
	Jun. 30, 2019
Balance Sheet Related Disclosures [Abstract]
Balance Sheet Details	Note 4 Prepaid expenses and other current assets consisted of the following as of June 30, 2019 and December 31, 2018: (in thousands) June 30, 2019 December 31, 2018 Prepaid expenses $ 1,659 $ 546 Other current assets 22 92 Total $ 1,681 $ 638 Property and equipment, net consisted of the following: (in thousands) June 30, 2019 December 31, 2018 Research equipment $ 3,001 $ 2,711 Computers and software 235 200 Office equipment and furniture 561 527 Leasehold improvements 35 34 Total 3,832 3,472 Less accumulated depreciation and amortization (1,846 ) (1,497 ) Property and equipment, net $ 1,986 $ 1,975 Depreciation and amortization expense was $0.2 million and $0.1 million Accrued liabilities consisted of the following as of June 30, 2019 and December 31, 2018: (in thousands) June 30, 2019 December 31, 2018 Accrued compensation $ 1,468 $ 974 Refundable fees received — 2,259 Current portion of operating lease liability 775 — Other accrued liabilities 1,254 674 Total $ 3,497 $ 3,907

Debt

Debt	6 Months Ended
	Jun. 30, 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 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. As a result of the equity purchase by Ultragenyx of 2.4 million shares of common stock (previously discussed at Note 2), the IND submission date and approval date have been extended to May 31, 2020 and June 30, 2020, respectively. 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 June 30, 2019, the Company is in compliance with all covenants and conditions of the Loan.

Stockholders' Equity

Stockholders' Equity	6 Months Ended
	Jun. 30, 2019
Stockholders Equity Note [Abstract]
Stockholders' Equity	Note 6. Stockholders’ Equity Equity Purchase Agreement On June 18, 2019, the Company entered into an Equity Purchase Agreement (the “Ultragenyx Agreement”) with Ultragenyx Pharmaceutical Inc. (“Ultragenyx”). Pursuant to the terms of the Ultragenyx Agreement, the Company sold an aggregate of 2,400,000 shares (the “Shares”) of common stock, par value $0.001 per share (“Common Stock”) at a price of $10.00 per share to Ultragenyx on June 19, 2019. Pursuant to the Ultragenyx Agreement, the Company also granted Ultragenyx a two-year option (the “Option”) to purchase up to 600,000 additional shares of Common Stock at a price of $16.00 per share. The Option to purchase additional shares of Common Stock may not be exercised if Ultragenyx’s ownership of the Company’s common stock would exceed 19.99% of the Company’s total shares outstanding following such exercise. The option was recorded as a component of stockholders’ equity within additional paid-in capital. Pursuant to the terms of the Ultragenyx Agreement, until the later of (i) the first anniversary of the closing date or (ii) the date on which Ultragenyx beneficially owns less than 8.0% of the total voting power of the Company, at each annual stockholders meeting or any stockholders meeting at which members of the board of directors (the “Board”) are to be elected, the Company must nominate one director designated by Ultragenyx (the “Ultragenyx Designee”). Additionally, the Ultragenyx Designee has the contractual right to be appointed to all Board committees (subject to applicable NASDAQ rules). Ultragenyx also has the right to have a designee attend Board meetings as a non-voting observer. Pursuant to the Ultragenyx Agreement, Ultragenyx agreed to customary standstill provisions and restrictions on transfer of the Shares. The standstill provisions and transfer restrictions last until June 19, 2021, and expire earlier upon the occurrence of certain events set forth in the Ultragenyx Agreement. The Ultragenyx Agreement contains customary representations, warranties and indemnification obligations of the parties. In connection with the Ultragenyx Agreement, the Company and Ultragenyx entered into a Registration Rights Agreement (the “Registration Rights Agreement”). The Registration Rights Agreement requires the Company to file a registration statement providing for the resale of the Shares within 180 days of June 18, 2019, and provides Ultragenyx with certain “piggy-back” registration rights with respect to registration statements that the Company may file. Restricted Common Shares In March 2013, the founders of the Company purchased 2,783,686 shares of common 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 three and six months ended June 30, 2019 as they were anti-dilutive totaled 93,407 and 80,585, respectively, and 81,056 and 87,028 for the three and six months ended June 30, 2018, respectively. For the three and six months ended June 30, 2019 and 2018, the calculation of the weighted-average number of shares outstanding excludes unvested restricted shares of common stock of 622,667.

Share-Based Compensation

Share-Based Compensation	6 Months Ended
	Jun. 30, 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 39,912 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 131,091 shares available for future issuance under the 2010 Plan as of June 30, 2019; however, the Company will not 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 Stock 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 stock options granted: For the Three Months Ended June 30, For the Six Months Ended June 30, 2019 2018 2019 2018 Expected life (in years) 6.1 7.3 6.1 7.3 Expected volatility 75.6 % 76.4 % 74.7 % 76.4 % Expected dividend yield — % — % — % — % Risk-free interest rate 2.30 % 1.87 % 2.42 % 1.87 % Grant date weighted average fair value $ 4.76 $ 7.94 $ 3.89 $ 7.94 The following table summarizes the Company’s stock option activity Number of Shares Weighted Average Exercise Price Weighted- Average Remaining Contractual Term (Years) Aggregate Intrinsic Value (in thousands) Outstanding - December 31, 2018 1,184,433 $ 7.41 Granted 126,000 * $ 5.82 Exercised (823 ) $ 1.03 Forfeited/cancelled (69,501 ) $ 8.07 Outstanding - June 30, 2019 1,240,109 $ 7.21 8.56 $ 2,770 Exercisable - June 30, 2019 373,533 $ 6.38 7.26 $ 1,150 Exercisable and expected to vest - June 30, 2019 1,240,109 $ 7.21 8.56 $ 2,770 * Total options granted during the first six-month period of 2019 excludes 160,000 options when granted were subject to stockholder approval pertaining to the Chief Executive Officer and Chief Financial Officer. At June 30, 2019, the total unrecognized compensation cost of $ 4.2 2.9 Share-based compensation expenses included in the Company’s condensed statements of operations and comprehensive loss for the three and six months ended June 30, 2019 and 2018 were: For the Three Months Ended June 30, For the Six Months Ended June 30, (in thousands) 2019 2018 2019 2018 Research and development $ 157 $ 7 $ 308 $ 15 General and administrative 246 133 494 151 Total $ 403 $ 140 $ 802 $ 166 Share-based compensation expense for the three and six months ended June 30, 2019 excludes expense related to options granted to the Chief Executive Officer and Chief Financial Officer as the option grants are subject to shareholder approval.

Leases

Leases	6 Months Ended
	Jun. 30, 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 the 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 a security deposit of $96,000 upon executing the lease which is included (along with additional funds required to secure the letter of credit) in the balance of 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 June 30, 2019, the payments of the operating lease liability were as follows: (in thousands) Remaining Lease Payments 2019 $ 622 2020 1,272 2021 1,310 2022 1,349 2023 1,390 Thereafter 1,745 Total remaining lease payments 7,688 Less: imputed interest (1,637 ) Total operating lease liabilities $ 6,051 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 and $0.6 million for the three and six months ended June 30, 2019.

Related Party Transactions

Related Party Transactions	6 Months Ended
	Jun. 30, 2019
Related Party Transactions [Abstract]
Related Party Transactions	Note 9. Related Party Transactions Ultragenyx On June 17, 2019, Arcturus and Ultragenyx executed Amendment 3. In addition, as a result of the Ultragenyx Agreement, Ultragenyx owns 18.3% of the outstanding common stock of the Company as of June 30, 2019. For the three and six months ended June 30, 2019, the Company has recognized revenue of $2.5 million and $3.9 million, respectively, and for the three and six months ended June 30, 2018, the Company recognized revenue of $1.2 million and $2.7 million. As of June 30, 2019 and 2018, the Company holds accounts receivable balances of a negligible amount and $0.4 million, respectively. (Note 2) 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 three and six months ended June 30, 2019, the Company has recognized revenue of 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. The Company has recorded $0.6 million of its share of losses of the investee leaving no equity investment balance as of June 30, 2019.

Subsequent Events

Subsequent Events	6 Months Ended
	Jun. 30, 2019
Subsequent Events [Abstract]
Subsequent Events	Note 10. Subsequent Events CureVac On July 26, 2019 Arcturus Therapeutics, Inc. (“Arcturus”), a subsidiary of the Company, entered into an amendment (the “CureVac Amendment”) to its Development and Option Agreement, as amended (the “Development and Option Agreement”), with CureVac AG (“CureVac”), pursuant to which Arcturus and CureVac agreed to (a) modify the time period during which CureVac may select potential targets to be licensed from the Company pursuant to the terms of the Development and Option Agreement, (b) reduce the overall number of maximum targets to be reserved and licensed from fifteen (15) to ten (10) targets, (c) simplify the process for selecting and reserving targets, (d) define conditions under which targets can be pre-restricted by Arcturus in connection with its own research and development activities and (e) restore CureVac’s original obligations with respect to the funding of scientists at Arcturus. In connection with the entry into the CureVac Amendment, on July 26, 2019, Arcturus and CureVac also entered into a Termination Agreement (the “Termination Agreement”) terminating the Co-Development and Co-Commercialization Agreement (the “Co-Development Agreement”) between the Company and CureVac dated as of January 1, 2018. The Termination Agreement is effective as of July 26, 2019. Pursuant to the Termination Agreement, CureVac agreed to make a one-time payment to Arcturus in the amount of $4,000,000 in consideration for such termination, including payments in connection with CureVac’s termination of co-development of ARCT-810 as a therapy for ornithine transcarbamylase (OTC) deficiency. The payment was collected during July 2019. The Termination Agreement includes a customary mutual release and a mutual non-disparagement clause and provides for the survival of the confidentiality provisions in the Co-Development Agreement. The foregoing description of the CureVac Amendment and the Termination Agreement does not purport to be complete and is qualified in its entirety by reference to the CureVac Amendment, a copy of which is filed hereto as Exhibit 10.20, and the Termination Amendment, a copy of which is filed hereto as Exhibit 10.21. Cystic Fibrosis Foundation On August 1, 2019, Arcturus Therapeutics, Inc. (“Arcturus Sub”), a subsidiary of the Company, entered into an amendment (the “CFF Amendment”) to its Development Program Letter Agreement of May 16, 2017, as amended by Amendment No. 1 dated July 13, 2018 (the “Underlying Agreement”) with the Cystic Fibrosis Foundation (“CFF”), pursuant to which Arcturus Sub and CFF agreed to: (a) increase the Amount of Award (as defined in the Underlying Agreement) from CFF to advance LUNAR-CF to $15.0 million from approximately $3.2 million, require Arcturus Sub to provide $5.0 million in matching funds for remaining budgeted costs, and modify the disbursement schedule from CFF to Arcturus related thereto such that (i) $4.0 million will be disbursed upon execution of the CFF Amendment, (ii) $2.0 million will be disbursed within 30 days of the first day of each of January, April, July and October 2020 upon Arcturus invoicing CFF to meet project goals, and (iii) the last payment of $3.0 million less the prior award previously paid out, equaling approximately $2.1 million, will be disbursed upon Arcturus Sub invoicing CFF to meet good manufacturing practices and opening an IND application; (b) replace the existing royalties due to CFF under the Underlying Agreement with specified royalties expressed as a percentage of net sales, subject to specified royalty caps expressed as a multiple of the Actual Award (as defined in the CFF Amendment) and expiration of the royalties upon specified time limitations or patent or exclusivity expiration, among other limitations and exclusions; (c) define conditions under which Arcturus Sub shall pay to CFF disposition payments in the event of a Disposition Transaction (as defined in the CFF Amendment), including a license, sale or other transfer of a Covered Product or Arcturus Development Program Technology (excluding Net Sales) or a Change of Control Transaction; (d) provide a termination right to CFF; and (e) make corresponding changes to exhibits, definitions and other provisions of the Underlying Agreement consistent with the Amendment, including the replacement of references to Cystic Fibrosis Foundation Therapeutics, Inc. with CFF to reflect the prior assignment of the Underlying Agreement to CFF. The foregoing description of the CFF Amendment does not purport to be complete and is qualified in its entirety by reference to the CFF Amendment, a copy of which is filed hereto as Exhibit 10.16. Registered Direct Offerings On July 26, 2019, the Company entered into an engagement letter (the “Letter Agreement”) with H.C. Wainwright & Co., LLC (the “Placement Agent”) relating to the Company’s registered direct offering of common stock (the “Offering”) to certain institutional investors (the “Investors”). Roth Capital Partners, LLC and Ladenburg Thalmann & Co. Inc. acted as financial advisors for the transaction. Pursuant to the Letter Agreement, the Company agreed to pay the Placement Agent a cash fee of 6.0% of the gross proceeds from the Offering raised from Investors and up to $75,000 for expenses. In addition, on August 1, 2019 and August 2, 2019, the Company and the Investors entered into securities purchase agreements relating to the issuance and sale of shares of common stock. The purchase price per share for each share offered to the Investors is $11.50. The aggregate gross proceeds of the Offering were $13.2 million, for the sale in the aggregate of 1,145,653 shares of common stock. The net proceeds to the Company from the Offering, after deducting Placement Agent fees and the Company’s estimated offering expenses, are expected to be approximately $12.2 million. The Offering closed on August 5, 2019. The offer and sale of the common stock was registered under the Securities Act of 1933, as amended (the “Securities Act”), on the Company’s Registration Statement on Form S-3 (Registration No. 333-232281), previously filed with the Securities and Exchange Commission and declared effective on July 29, 2019.

Description of Business, Basi_2

Description of Business, Basis of Presentation and Summary of Significant Accounting Policies (Policies)	6 Months Ended
	Jun. 30, 2019
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation The accompanying condensed consolidated financial statements include the accounts of Arcturus Therapeutics Holdings Inc. 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, 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
Liquidity	Liquidity 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 June 18, 2019, the Company entered into a Third Amendment to the Research Collaboration and License Agreement (the “Third Amendment”) with Ultragenyx Pharmaceutical Inc. (“Ultragenyx”), from which the Company received $30.0 million (Note 2). 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 June 30, 2019 has an accumulated deficit of $53.2 million.
Recent Developments	Recent Developments Arcturus Therapeutics Ltd. (“Arcturus Israel”) completed the process to redomicile from an Israeli limited company to a Delaware corporation (the “Redomiciliation”). On February 11, 2019, Arcturus Israel filed an application with the Tel-Aviv District Court (the “Israeli Court”) to approve the convening of a general shareholders meeting of Arcturus Israel 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 Securities and Exchange Commission 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, held on May 17, 2019, as described in the Form S-4. The general shareholders meeting resulted in the approval of the Redomiciliation, and Arcturus Israel then approached the Israeli Court and requested its approval of the Redomiciliation. In connection with the Redomiciliation, Arcturus Israel entered into a share exchange agreement (the “Exchange Agreement”) with a special-purpose company, Arcturus Therapeutics Holdings Inc., the reporting company and parent to Arcturus Therapeutics, Inc. (“Arcturus Sub”). In furtherance of the Redomiciliation, and pursuant to the terms of the Exchange Agreement, the holders of ordinary shares of Arcturus Israel as of a future record date and the holders of options to purchase ordinary shares of Arcturus Israel as of the same record date transferred their ordinary shares of Arcturus Israel and options to purchase ordinary shares of Arcturus Israel, respectively, to the Company and, in exchange thereof, received one share of common stock of the Company for each ordinary share of Arcturus Israel and an option to purchase one share of common stock of the Company in exchange for each ordinary share of Arcturus Israel underlying the existing option to be so exchanged, respectively. As a result of the Exchange Agreement, the par value of Arcturus Israel’s ordinary shares prior to the Redomiciliation is presented in New Israeli Shekel (“NIS”) and the par value of the Company’s common stock subsequent to the Redomiciliation is presented in United States Dollars (“USD”). As of June 17, 2019, the common stock of the Company is listed on the NASDAQ Stock Market LLC (“NASDAQ”). Upon consummation of the transactions contemplated by the Share Exchange Agreement, Arcturus Israel’s ordinary shares were delisted from trading on NASDAQ, and Arcturus Israel became a private company (as defined in the Companies Law) wholly-owned by the Company. Pursuant to the Exchange Agreement, on June 12, 2019 all of the shares of Arcturus Sub were distributed to the Company and Arcturus Sub become a wholly-owned and direct subsidiary of the Company. This distribution was completed in connection with a liquidation of Arcturus Israel which was formally initiated after the redomiciliation described above. See “Note 10. Subsequent Events”
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 upfront 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 performs 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 assessments 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, preclinical studies 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) June 30, 2019 June 30, 2018 Cash and cash equivalents $ 55,840 $ 29,322 Non-current restricted cash 107 107 Total cash, cash equivalents and restricted cash shown in the statement of cash flows $ 55,947 $ 29,429
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 shares of common stock outstanding for the period, without consideration for common stock equivalents. Diluted net loss per share is calculated by dividing the net loss by the weighted-average number of shares of common stock and dilutive common stock equivalents outstanding for the period determined using the treas ury-stock method. Dilutive shares of common stock are comprised of stock 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. 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 $6.4 million on January 1, 2019, with a corresponding right-of-use asset of $5.9 million based on the present value of the remaining minimum rental payments. See Note 8 for further discussion.

Description of Business, Basi_3

Description of Business, Basis of Presentation and Summary of Significant Accounting Policies (Tables)	6 Months Ended
	Jun. 30, 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) June 30, 2019 June 30, 2018 Cash and cash equivalents $ 55,840 $ 29,322 Non-current restricted cash 107 107 Total cash, cash equivalents and restricted cash shown in the statement of cash flows $ 55,947 $ 29,429

Collaboration Revenue (Tables)

Collaboration Revenue (Tables)	6 Months Ended
	Jun. 30, 2019
Collaboration Agreements [Abstract]
Summary of Changes in Balances of Contract Assets and Contract Liability	The following table presents changes during the six months ended June 30, 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 - December 31, 2018 $ 4,480 Additions for advanced billings 11,038 Deductions for cash collections (9,701 ) BALANCE – June 30, 2019 $ 5,817 (in thousands) Contract Liabilities BALANCE - December 31, 2018 $ 13,806 Additions for advanced billings 27,650 Additions for promised goods/services to be provided in current and future periods in connection with Topic 606 adoption 803 Deductions for promised goods/services provided in current period (14,877 ) BALANCE – June 30, 2019 $ 27,382

Balance Sheet Details (Tables)

Balance Sheet Details (Tables)	6 Months Ended
	Jun. 30, 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 June 30, 2019 and December 31, 2018: (in thousands) June 30, 2019 December 31, 2018 Prepaid expenses $ 1,659 $ 546 Other current assets 22 92 Total $ 1,681 $ 638
Summary of Components of Property and Equipment, Net	Property and equipment, net consisted of the following: (in thousands) June 30, 2019 December 31, 2018 Research equipment $ 3,001 $ 2,711 Computers and software 235 200 Office equipment and furniture 561 527 Leasehold improvements 35 34 Total 3,832 3,472 Less accumulated depreciation and amortization (1,846 ) (1,497 ) Property and equipment, net $ 1,986 $ 1,975
Schedule of Accrued Liabilities	Accrued liabilities consisted of the following as of June 30, 2019 and December 31, 2018: (in thousands) June 30, 2019 December 31, 2018 Accrued compensation $ 1,468 $ 974 Refundable fees received — 2,259 Current portion of operating lease liability 775 — Other accrued liabilities 1,254 674 Total $ 3,497 $ 3,907

Share-Based Compensation (Table

Share-Based Compensation (Tables)	6 Months Ended
	Jun. 30, 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 stock options granted: For the Three Months Ended June 30, For the Six Months Ended June 30, 2019 2018 2019 2018 Expected life (in years) 6.1 7.3 6.1 7.3 Expected volatility 75.6 % 76.4 % 74.7 % 76.4 % Expected dividend yield — % — % — % — % Risk-free interest rate 2.30 % 1.87 % 2.42 % 1.87 % Grant date weighted average fair value $ 4.76 $ 7.94 $ 3.89 $ 7.94
Summary of Stock Option Activity	The following table summarizes the Company’s stock option activity Number of Shares Weighted Average Exercise Price Weighted- Average Remaining Contractual Term (Years) Aggregate Intrinsic Value (in thousands) Outstanding - December 31, 2018 1,184,433 $ 7.41 Granted 126,000 * $ 5.82 Exercised (823 ) $ 1.03 Forfeited/cancelled (69,501 ) $ 8.07 Outstanding - June 30, 2019 1,240,109 $ 7.21 8.56 $ 2,770 Exercisable - June 30, 2019 373,533 $ 6.38 7.26 $ 1,150 Exercisable and expected to vest - June 30, 2019 1,240,109 $ 7.21 8.56 $ 2,770 * Total options granted during the first six-month period of 2019 excludes 160,000 options when granted were subject to stockholder approval pertaining to the Chief Executive Officer and Chief Financial Officer.
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 and six months ended June 30, 2019 and 2018 were: For the Three Months Ended June 30, For the Six Months Ended June 30, (in thousands) 2019 2018 2019 2018 Research and development $ 157 $ 7 $ 308 $ 15 General and administrative 246 133 494 151 Total $ 403 $ 140 $ 802 $ 166

Leases (Tables)

Leases (Tables)	6 Months Ended
	Jun. 30, 2019
Leases [Abstract]
Payments of Operating Lease Liability	As of June 30, 2019, the payments of the operating lease liability were as follows: (in thousands) Remaining Lease Payments 2019 $ 622 2020 1,272 2021 1,310 2022 1,349 2023 1,390 Thereafter 1,745 Total remaining lease payments 7,688 Less: imputed interest (1,637 ) Total operating lease liabilities $ 6,051 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)	Jun. 18, 2019USD ($)	Jan. 01, 2019USD ($)	Oct. 12, 2018USD ($)	Jun. 30, 2019USD ($)Segment	Jun. 30, 2018USD ($)	Feb. 11, 2019shares	Dec. 31, 2018USD ($)
Summary Of Significant Accounting Policy [Line Items]
Accumulated deficit				$ (53,246,000)			$ (44,874,000)
Number of ordinary share of company in exchange for each ordinary share | shares						1
Number of operating segment for research and development | Segment				1
Dividends declared or paid				$ 0	$ 0
Increase in deferred revenue due to adoption of new revenue recognition				12,773,000	$ 5,542,000
Operating lease liability				6,051,000
Operating lease right-of-use asset				$ 5,509,000
Office and Lab Space [Member]
Summary Of Significant Accounting Policy [Line Items]
Operating lease liability		$ 6,400,000
Operating lease right-of-use asset		5,900,000
ASC 606 [Member]
Summary Of Significant Accounting Policy [Line Items]
Increase in deferred revenue due to adoption of new revenue recognition		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
Research Collaboration and License Agreement [Member] | Ultragenyx [Member]
Summary Of Significant Accounting Policy [Line Items]
Third amendment fee received	$ 30,000,000

Schedule of Cash and Cash Equiv

Schedule of Cash and Cash Equivalents and Restricted Cash (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018	Jun. 30, 2018	Dec. 31, 2017
Accounting Policies [Abstract]
Cash and cash equivalents	$ 55,840	$ 36,709	$ 29,322
Non-current restricted cash	107	107	107
Total cash, cash equivalents and restricted cash shown in the statement of cash flows	$ 55,947	$ 36,816	$ 29,429	$ 25,238

Collaboration Revenue - Summary

Collaboration Revenue - Summary of Changes in Balances of Contract Assets and Contract Liability (Details) $ in Thousands	6 Months Ended
	Jun. 30, 2019USD ($)
Collaboration Agreements [Abstract]
Contract Assets, Balance	$ 4,480
Contract Assets, Additions for advanced billings	11,038
Contract Assets, Deductions for cash collections	(9,701)
Contract Assets, Balance	5,817
Contract Liabilities, Balance	13,806
Contract Liabilities, Additions for advanced billings	27,650
Additions for promised goods/services to be provided in current and future periods in connection with Topic 606 adoption	803
Deductions for promised goods/services provided in current period	(14,877)
Contract Liabilities, Balance	$ 27,382

Collaboration Revenue (Details

Collaboration Revenue (Details Textual)	Jun. 18, 2019USD ($)Target$ / sharesshares	Feb. 11, 2019USD ($)	Jan. 01, 2019USD ($)	Jun. 30, 2019USD ($)shares	Dec. 31, 2018USD ($)shares	Jun. 30, 2018USD ($)	Jun. 30, 2019USD ($)Performanceshares	Jun. 30, 2018USD ($)	Dec. 31, 2017USD ($)	Jun. 16, 2019Target
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Deferred revenue				$ 27,382,000	$ 13,806,000		$ 27,382,000
Collaboration revenue				$ 10,153,000		$ 2,386,000	$ 14,503,000	$ 4,753,000
Purchase of common stock, shares | shares				13,120,000	10,762,000		13,120,000
Increase in deferred revenue due to adoption of new revenue recognition							$ 12,773,000	5,542,000
Other Collaboration Revenue [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Collaboration revenue				$ 3,600,000		700,000	4,100,000	1,200,000
ASC 606 [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Increase in deferred revenue due to adoption of new revenue recognition			$ 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			0
Adjustments to transaction price							$ 0
Number of performance obligation | Performance							1
Deferred revenue				6,200,000	$ 6,500,000		$ 6,200,000
Collaboration revenue				600,000		200,000	1,100,000	300,000
Research Collaboration And Exclusive License Agreement [Member] | Collaboration Partner - Ultragenyx [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Upfront payment received	$ 6,000,000
Revenue recognition potential milestone revenue recognized							139,000,000
Collaboration revenue				2,500,000		1,200,000	3,900,000	2,700,000
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.
Percentage of reduction in option exercise fees, milestone payments and royalty rates							50.00%
Revenue recognized as one time payment									$ 2,000,000
Annual maintenance fee					1,500,000
Number of targets | Target	12									10
Purchase of common stock, shares | shares	2,400,000
Ownership interest of common stock	18.30%						18.30%
Purchase of additional shares of common stock | shares	600,000
Purchase of additional shares of common stock price per share | $ / shares	$ 16
Consideration received	$ 30,000,000
Consideration received for common stock purchase	24,000,000
Transaction price	14,400,000
Premium paid for purchase of common stock	$ 8,400,000
Lack of marketability discount restricted period	2 years
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			$ 0
Number of performance obligation | Performance							1
Deferred revenue				14,500,000	2,700,000		$ 14,500,000
Collaboration revenue				2,500,000		1,200,000	3,900,000	2,700,000
Transaction price							$ 14,400,000
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.
Cumulative catch-up amount added to transaction price upon amendment							$ 2,000,000
Cumulative catch up adjustment							$ 1,100,000
Revenue recognition, reserve target exclusivity period							4 years
Increase in deferred revenue due to adoption of new revenue recognition							$ 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			0
Adjustments to transaction price							$ 0
Number of performance obligation | Performance							1
Deferred revenue				4,000,000	$ 4,400,000		$ 4,000,000
Collaboration revenue				3,400,000		$ 300,000	5,300,000	$ 500,000
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 [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Collaboration agreement termination date		Feb. 11, 2019
Percentage of global rights reassumed		100.00%
Collaboration agreement settlement obligation settled amount		$ 4,000,000
Research And Exclusive License Agreement [Member] | Synthetic Genomics, Inc [Member] | Other Collaboration Revenue [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Collaboration revenue				$ 3,300,000			$ 3,500,000
Other collaboration agreement date				2017-10
Sublicense revenue recognized				$ 3,300,000
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
Minimum [Member] | Research Collaboration And Exclusive License Agreement [Member] | Collaboration Partner - Ultragenyx [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Option exercise revenue range per target	$ 500,000						2,000,000
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
Maximum [Member] | Research Collaboration And Exclusive License Agreement [Member] | Collaboration Partner - Ultragenyx [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Option exercise revenue range per target	$ 1,500,000						$ 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	Jun. 30, 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: 2019-07-01
Revenue Remaining Performance Obligation Expected Timing Of Satisfaction [Line Items]
Remaining research period	21 months
Remaining performance obligation	$ 23.6

Balance Sheet Details - Schedul

Balance Sheet Details - Schedule of Prepaid Expenses and Other Current Assets (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Prepaid Expenses And Other Current Assets [Abstract]
Prepaid expenses	$ 1,659	$ 546
Other current assets	22	92
Total	$ 1,681	$ 638

Balance Sheet Details - Summary

Balance Sheet Details - Summary of Components of Property and Equipment, Net (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Property Plant And Equipment [Line Items]
Property and equipment, gross	$ 3,832	$ 3,472
Less accumulated depreciation and amortization	(1,846)	(1,497)
Property and equipment, net	1,986	1,975
Research equipment [Member]
Property Plant And Equipment [Line Items]
Property and equipment, gross	3,001	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		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Balance Sheet Related Disclosures [Abstract]
Depreciation and amortization	$ 200	$ 100	$ 349	$ 256

Balance Sheet Details - Sched_2

Balance Sheet Details - Schedule of Accrued Liabilities (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Accrued Liabilities Current [Abstract]
Accrued compensation	$ 1,468	$ 974
Refundable fees received		2,259
Current portion of operating lease liability	775
Other accrued liabilities	1,254	674
Total	$ 3,497	$ 3,907

Debt (Details Textual)

Debt (Details Textual) - Loan and Security Agreement [Member] - Western Alliance Bank [Member] - Long-term Debt [Member] - USD ($) shares in Millions	Oct. 12, 2018	Jun. 30, 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 origination 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 Western Alliance Bank.
Debt instrument, collateral amount	20,000,000
Available sale of equity securities	$ 15,000,000
Ultragenyx [Member] | Common Stock [Member]
Debt Instrument [Line Items]
Stock issued during period	2.4
Minimum [Member]
Debt Instrument [Line Items]
Percentage required to be maintain in deposit and investment	50.00%

Stockholders' Equity (Details T

Stockholders' Equity (Details Textual)	Jun. 19, 2019$ / sharesshares	Jun. 18, 2019	Mar. 31, 2013$ / sharesshares	Jun. 30, 2019$ / sharesshares	Jun. 30, 2018shares	Jun. 30, 2019$ / sharesshares	Jun. 30, 2018shares	Dec. 31, 2017USD ($)Milestoneshares	Dec. 31, 2018₪ / sharesshares	Dec. 31, 2016Milestone	Dec. 31, 2014shares
Class Of Stock [Line Items]
Common stock, shares issued				13,120,000		13,120,000			10,762,000
Common stock, par value | (per share)				$ 0.001		$ 0.001			₪ 0.07
Antidilutive securities excluded from computation of earnings per share				93,407	81,056	80,585	87,028
Unvested Restricted Ordinary Shares [Member]
Class Of Stock [Line Items]
Antidilutive securities excluded from computation of earnings per share				622,667	622,667	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	622,667	622,667	622,667				769,176
Accelerated ordinary shares vested								146,510
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%
Equity Purchase Agreement [Member] | Collaboration Partner - Ultragenyx [Member]
Class Of Stock [Line Items]
Common stock, shares issued	2,400,000
Common stock, par value | $ / shares	$ 0.001
Common stock price per share | $ / shares	$ 10
Purchase of additional shares of common stock	600,000
Purchase of additional shares of common stock price per share | $ / shares	$ 16
Equity Purchase Agreement [Member] | Collaboration Partner - Ultragenyx [Member] | Maximum [Member]
Class Of Stock [Line Items]
Ownership interest of common stock	8.00%
Registration Rights Agreement | Collaboration Partner - Ultragenyx [Member]
Class Of Stock [Line Items]
Percentage of minimum common stock may not exercised total shares outstanding		19.99%
Registration Rights Agreement | Collaboration Partner - Ultragenyx [Member] | Maximum [Member]
Class Of Stock [Line Items]
Period to register sale of shares		180 days

Share-Based Compensation (Detai

Share-Based Compensation (Details Textual) $ in Millions	1 Months Ended	6 Months Ended
	Jun. 30, 2019USD ($)shares	Jun. 30, 2019USD ($)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
Options granted		126,000
Compensation cost not yet recognized | $	$ 4.2	$ 4.2
Weighted-average remaining service period		2 years 10 months 24 days
Fair value of options vested | $		$ 0.6
Chief Executive Officer And Chief Financial Officer [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Options granted		160,000
2013 Equity Incentive Plan [Member] | Stock Option [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares authorized for grant	0	0
Share options expiration period		10 years
Common stock reserved for future issuance	39,912	39,912
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	131,091	131,091
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	220,250	220,250
Shares issued in period	243,750
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
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]
Options granted	160,000
2019 Omnibus Equity Incentive Plan [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares authorized for grant			2,600,000
Common stock reserved for future issuance			1,199,891

Share-Based Compensation (Det_2

Share-Based Compensation (Details) - $ / shares	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Grant date weighted average fair value	$ 4.76	$ 7.94	$ 3.89	$ 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	6 years 1 month 6 days	7 years 3 months 18 days
Expected volatility	75.60%	76.40%	74.70%	76.40%
Risk-free interest rate	2.30%	1.87%	2.42%	1.87%

Share-Based Compensation (Det_3

Share-Based Compensation (Details 1) - USD ($) $ / shares in Units, $ in Thousands	6 Months Ended
	Jun. 30, 2019
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Number of Shares, Outstanding	1,184,433
Number of Shares, Granted	126,000
Number of Shares, Exercised	(823)
Number of Shares, Forfeited/cancelled	(69,501)
Number of Shares, Outstanding	1,240,109
Number of Shares, Exercisable - June 30, 2019	373,533
Number of Shares, Exercisable and expected to vest - June 30, 2019	1,240,109
Weighted-Average Exercise Price, Outstanding	$ 7.41
Weighted-Average Exercise Price, Granted	5.82
Weighted-Average Exercise Price, Exercised	1.03
Weighted-Average Exercise Price, Forfeited/cancelled	8.07
Weighted-Average Exercise Price, Outstanding - June 30, 2019	7.21
Weighted-Average Exercise Price, Exercisable - June 30, 2019	6.38
Weighted-Average Exercise Price, Exercisable and expected to vest - June 30, 2019	$ 7.21
Weighted-Average Remaining Contractual Term (Years), Outstanding - June 30, 2019	8 years 6 months 21 days
Weighted-Average Remaining Contractual Term (Years), Exercisable - June 30, 2019	7 years 3 months 3 days
Weighted-Average Remaining Contractual Term (Years), Exercisable and expected to vest June 30, 2019	8 years 6 months 21 days
Aggregate Intrinsic Value, Outstanding June 30, 2019	$ 2,770
Aggregate Intrinsic Value, Exercisable June 30, 2019	1,150
Aggregate Intrinsic Value, Exercisable and expected to vest June 30, 2019	$ 2,770

Share-Based Compensation (Det_4

Share-Based Compensation (Details 1) (Parenthetical)	6 Months Ended
	Jun. 30, 2019shares
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Options granted	126,000
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		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share-based compensation expenses	$ 403	$ 140	$ 802	$ 166
Research and Development [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share-based compensation expenses	157	7	308	15
General and Administrative [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share-based compensation expenses	$ 246	$ 133	$ 494	$ 151

Leases (Details Textual)

Leases (Details Textual) - USD ($)	1 Months Ended	3 Months Ended	6 Months Ended
	Oct. 31, 2017	Jun. 30, 2019	Jun. 30, 2019
Lessee Lease Description [Line Items]
Operating lease, remaining lease term		6 years	6 years
Operating lease costs		$ 300,000	$ 600,000
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 the then current market rate with annual escalations;
Security deposit	$ 96,000

Leases - Payments of Operating

Leases - Payments of Operating Lease Liability (Details) $ in Thousands	Jun. 30, 2019USD ($)
Leases [Abstract]
2019	$ 622
2020	1,272
2021	1,310
2022	1,349
2023	1,390
Thereafter	1,745
Total remaining lease payments	7,688
Less: imputed interest	(1,637)
Total operating lease liabilities	$ 6,051
Weighted-average remaining lease term	6 years
Weighted-average discount rate	8.40%

Related Party Transactions - Ul

Related Party Transactions - Ultragenyx (Details Textual) - USD ($) $ in Thousands	Jun. 18, 2019	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Related Party Transaction [Line Items]
Collaboration revenue		$ 10,153	$ 2,386	$ 14,503	$ 4,753
Research Collaboration And Exclusive License Agreement [Member] | Collaboration Partner - Ultragenyx [Member]
Related Party Transaction [Line Items]
Ownership interest of common stock	18.30%			18.30%
Collaboration revenue		2,500	1,200	$ 3,900	2,700
Accounts receivable, balance amount		$ 400	$ 400	$ 400	$ 400

Related Party Transactions - Pr

Related Party Transactions - Providence (Details Textual) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Related Party Transaction [Line Items]
Revenue	$ 10,153	$ 2,386	$ 14,503	$ 4,753
Providence Therapeutics, Inc [Member] | Research Collaboration and License Agreement [Member]
Related Party Transaction [Line Items]
Revenue	$ 300	$ 100	$ 300	$ 100

Related Party Transactions - Eq

Related Party Transactions - Equity-Method Investment (Details Textual) - USD ($)	3 Months Ended	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018
Related Party Transaction [Line Items]
Share of losses for investee	$ 47,000	$ 288,000	$ 47,000
Equity investments				$ 288,000
ADAIR Technology [Member]
Related Party Transaction [Line Items]
Equity method ownership percentage	30.00%		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%		20.00%

Subsequent Events (Details Text

Subsequent Events (Details Textual)	Aug. 02, 2019USD ($)$ / sharesshares	Jul. 26, 2019USD ($)Target	Jul. 13, 2019USD ($)	Jul. 12, 2019USD ($)	Jun. 30, 2019USD ($)	Jul. 25, 2019Target
Subsequent Event [Line Items]
Gross proceeds from offering					$ 15,545,000
Subsequent Events [Member] | Letter Agreement [Member] | Common Stock [Member] | H.C. Wainwright & Co., LLC [Member]
Subsequent Event [Line Items]
Percentage of cash fee on gross proceeds from offering		6.00%
Subsequent Events [Member] | Securities Purchase Agreement [Member] | Common Stock [Member] | H.C. Wainwright & Co., LLC [Member]
Subsequent Event [Line Items]
Net proceeds from offering after deducting placement agent fees and offering expenses	$ 12,200,000
Closing date of offering	Aug. 5, 2019
Subsequent Events [Member] | Securities Purchase Agreement [Member] | Common Stock [Member] | H.C. Wainwright & Co., LLC [Member] | Investor
Subsequent Event [Line Items]
Purchase price per share | $ / shares	$ 11.50
Gross proceeds from offering	$ 13,200,000
Common stock, shares issued | shares	1,145,653
Subsequent Events [Member] | Collaboration Partner Cure Vac Entered Into Co Development Agreement [Member] | Termination Agreement [Member]
Subsequent Event [Line Items]
Collaboration agreement settlement obligation one time settled amount		$ 4,000,000
Subsequent Events [Member] | Cystic Fibrosis Foundation [Member] | Underlying Agreement [Member]
Subsequent Event [Line Items]
Payments for matching funds for remaining budgeted costs			$ 5,000,000
Disbursed amount upon execution of amendment			4,000,000
Final payment of disbursement amount			3,000,000
Disbursement payment upon achievement of required manufacturing practices and IND application			2,100,000
Subsequent Events [Member] | Cystic Fibrosis Foundation [Member] | Underlying Agreement [Member] | Disbursement Due January 2020 [Member]
Subsequent Event [Line Items]
Disbursement amount payable upon achievement of project goal			2,000,000
Subsequent Events [Member] | Cystic Fibrosis Foundation [Member] | Underlying Agreement [Member] | Disbursement Due April 2020 [Member]
Subsequent Event [Line Items]
Disbursement amount payable upon achievement of project goal			2,000,000
Subsequent Events [Member] | Cystic Fibrosis Foundation [Member] | Underlying Agreement [Member] | Disbursement Due July 2020 [Member]
Subsequent Event [Line Items]
Disbursement amount payable upon achievement of project goal			2,000,000
Subsequent Events [Member] | Cystic Fibrosis Foundation [Member] | Underlying Agreement [Member] | Disbursement Due October 2020 [Member]
Subsequent Event [Line Items]
Disbursement amount payable upon achievement of project goal			2,000,000
Subsequent Events [Member] | Cystic Fibrosis Foundation [Member] | Underlying Agreement [Member] | LUNAR-CF [Member]
Subsequent Event [Line Items]
Payments for advance			$ 15,000,000	$ 3,200,000
Subsequent Events [Member] | Maximum [Member] | Letter Agreement [Member] | Common Stock [Member] | H.C. Wainwright & Co., LLC [Member]
Subsequent Event [Line Items]
Payments of stock issuance expenses		$ 75,000
Subsequent Events [Member] | Maximum [Member] | CureVac [Member]
Subsequent Event [Line Items]
Number of targets | Target		10				15