Eloxx Pharmaceuticals (ELOX) 10-Q 6 Nov 19 2019 Q3 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	9 Months Ended
	Sep. 30, 2019	Nov. 01, 2019
Document And Entity Information [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Sep. 30, 2019
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	Q3
Trading Symbol	ELOX
Entity Registrant Name	ELOXX PHARMACEUTICALS, INC.
Entity Central Index Key	0001035354
Current Fiscal Year End Date	--12-31
Entity Filer Category	Accelerated Filer
Entity Common Stock, Shares Outstanding		40,002,654
Entity Small Business	true
Entity Emerging Growth Company	false
Entity File Number	001-31326
Entity Tax Identification Number	841368850
Entity Address Line One	950 Winter Street
Entity Address City	Waltham
Entity Address State	Massachusetts
Entity Address Postal Zip Code	02451
City Area Code	781
Local Phone Number	577-5300
Entity Shell Company	false
Entity Current Reporting Status	Yes

Condensed Consolidated Balance

Condensed Consolidated Balance Sheets - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Current assets:
Cash and cash equivalents	$ 22,155	$ 48,606
Marketable securities	42,781
Restricted bank deposit	40	45
Prepaid expenses and other current assets	1,878	1,690
Total current assets	66,854	50,341
Property and equipment, net	220	248
Operating lease right-of-use asset	870
Other long-term assets	113	129
Total assets	68,057	50,718
Current liabilities:
Accounts payable	1,687	747
Accrued expenses	5,145	6,938
Current portion of long-term debt	3,488
Advances from collaboration partners	403
Current portion of operating lease liability	461
Taxes payable	43	122
Total current liabilities	11,227	7,807
Long-term debt	11,193
Operating lease liability	409
Stockholders’ equity:
Preferred stock, $0.01 par value per share, 5,000,000 shares authorized, no shares issued and outstanding at September 30, 2019 and December 31, 2018
Common stock, $0.01 par value per share, 500,000,000 shares authorized, 40,117,186 and 35,951,537 shares issued and 39,977,654 and 35,860,114 shares outstanding as of September 30, 2019 and December 31, 2018, respectively	404	360
Common stock in treasury, at cost, 139,532 and 91,423 shares at September 30, 2019 and December 31, 2018, respectively	(1,585)	(1,129)
Additional paid-in capital	171,783	129,825
Accumulated other comprehensive income	12
Accumulated deficit	(125,386)	(86,145)
Total stockholders’ equity	45,228	42,911
Total liabilities and stockholders' equity	$ 68,057	$ 50,718

Condensed Consolidated Balanc_2

Condensed Consolidated Balance Sheets (Parenthetical) - $ / shares	Sep. 30, 2019	Dec. 31, 2018
Statement Of Financial Position [Abstract]
Preferred stock, par value	$ 0.01	$ 0.01
Preferred Stock, shares authorized	5,000,000	5,000,000
Preferred stock, shares issued	0	0
Preferred Stock, shares outstanding	0	0
Common stock, par value	$ 0.01	$ 0.01
Common stock, shares authorized	500,000,000	500,000,000
Common stock, shares issued	40,117,186	35,951,537
Common stock, shares outstanding	39,977,654	35,860,114
Common stock, treasury shares	139,532	91,423

Condensed Consolidated Statemen

Condensed Consolidated Statements of Operations and Other Comprehensive Loss - USD ($) $ in Thousands		3 Months Ended		9 Months Ended
		Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Operating expenses:
Research and development		$ 6,801	$ 5,415	$ 20,160	$ 13,959
General and administrative		5,978	5,945	18,907	18,898
Reverse merger related expenses					594
Total operating expenses		12,779	11,360	39,067	33,451
Loss from operations		(12,779)	(11,360)	(39,067)	(33,451)
Other expense (income), net		96	(199)	174	(293)
Net loss		(12,875)	(11,161)	(39,241)	(33,158)
Other Comprehensive Loss:
Net loss		(12,875)	(11,161)	(39,241)	(33,158)
Unrealized gain (loss) from available-for-sale securities		(12)		12
Comprehensive loss		$ (12,887)	$ (11,161)	$ (39,229)	$ (33,158)
Basic and diluted net loss per share		$ (0.32)	$ (0.32)	$ (1.05)	$ (1.05)
Weighted average number of common shares in computing basic and diluted net loss per share	[1]	39,944,324	35,005,979	37,394,310	31,485,067
[1]	The following potentially dilutive securities have been excluded from the computation of diluted weighted average shares outstanding as their effect would be anti-dilutive: Nine months ended September 30, 2019 2018 Options to purchase common stock 4,797,040 3,611,400 Restricted stock units 508,228 767,743 Warrants 323,894 347,241 Total potential common stock equivalents 5,629,162 4,726,384

Condensed Consolidated Statem_2

Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018
Cash flows from operating activities:
Net loss	$ (39,241)	$ (33,158)
Adjustments to reconcile net loss to net cash used in operating activities:
Stock-based compensation	8,631	9,608
Depreciation	68	121
Loss on disposal of property and equipment		12
Amortization of operating lease right-of-use asset	350
Amortization of debt discount	378
Amortization of premium and discount on investment	(228)
Changes in operating assets and liabilities:
Prepaid expenses and other current assets	(150)	(401)
Other assets		(41)
Advances from collaboration partners	403
Accounts payable	940	(178)
Accrued expenses	(856)	1,730
Operating lease liabilities	(350)
Taxes payable	(79)
Net cash used in operating activities	(30,134)	(22,307)
Cash flows from investing activities:
Purchases of marketable securities	(56,041)
Proceeds from maturity of marketable securities	13,500	6
Purchases of property and equipment	(40)	(133)
Cash paid for long-term deposits	(22)	(11)
Net cash used in investing activities	(42,603)	(138)
Cash flows from financing activities:
Proceeds from debt financing obligation	15,000
Payment of debt issuance costs	(276)
Payment for settlement of taxes upon vesting of restricted stock securities	(1,215)
Proceeds from issuance of common stock on share-based compensation arrangements	148	103
Net cash provided by financing activities	46,281	53,676
(Decrease) increase in cash, cash equivalents and restricted cash	(26,456)	31,231
Cash, cash equivalents and restricted cash, beginning of period	48,651	24,151
Cash, cash equivalents and restricted cash, end of period	22,195	55,382
Reconciliation of cash, cash equivalents and restricted cash to condensed consolidated balance sheets
Cash and cash equivalents	22,155	55,336
Restricted cash included in restricted bank deposit	40	46
Total cash, cash equivalents and restricted cash	22,195	55,382
Supplemental disclosure of cash flow activities
Cash paid for interest	703
Cash paid for income taxes	79
Capital expenditures in liabilities for purchases of property, plant and equipment		104
Supplemental disclosure of non-cash financing activities
Non-cash acquisition of treasury shares	46	83
Non-cash issuance of shares upon exercise of warrants	178
Fair value of warrants issued in connection with long-term debt	421
Underwritten Public Offering [Member]
Cash flows from financing activities:
Proceeds from issuance of common stock	32,169	$ 53,573
Equity Sales Agreement [Member]
Cash flows from financing activities:
Proceeds from issuance of common stock	$ 455

Nature of the Business

Nature of the Business	9 Months Ended
	Sep. 30, 2019
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Nature of the Business	1. Nature of the Business Eloxx Pharmaceuticals, Inc., together with its subsidiaries (collectively “Eloxx” or the “Company”), is a clinical-stage biopharmaceutical company developing novel ribonucleic acid (RNA)-modulating drug candidates, each designed to be a eukaryotic ribosomal selective glycoside (ERSG), formulated to treat rare and ultra-rare premature stop codon diseases. Premature stop codons are point mutations that disrupt the stability of the impacted messenger RNA (mRNA) and the protein synthesis from that mRNA. As a consequence, patients with premature stop codon diseases have reduced levels of, or no, protein from a gene whose product performs an essential function. This type of mutation accounts for some of the most severe phenotypes across genetic diseases. Nonsense mutations have been identified in over 1,800 rare and ultra-rare diseases. Read-through therapeutic development is focused on increasing mRNA stability and enabling functional protein synthesis. As opposed to a typical gene therapy approach of targeting a single, unique mutation in a target disease, this small molecule strategy enables targeting an entire class of mutations across the rare disease landscape. The small molecule approach has the potential to address a range of different premature stop codons in a single gene since the ERSG compounds are targeted to the ribosomes. ELX-02, the Company’s lead investigational drug product candidate, is a small molecule designed to restore production of full-length functional proteins. ELX-02 is in clinical development for systemic administration for cystic fibrosis and nephropathic cystinosis. ELX-02 is an investigational drug that has not been approved by any global regulatory body. In addition, the Company recently announced a new program studying intravitreal administration of ERSG compounds for rare inherited retinal disorders with an initial focus on Usher Syndrome. During the quarter ended September The Company . The Company’s research and development strategy is to target rare or ultra-rare diseases where a high unmet medical need exists, a nonsense mutation-bearing patient population is established, preclinical read-through can be established in predictive personalized medicine models, and a defined path through Orphan Drug development, regulatory approval, patient access and commercialization is identified. The Company believes patient advocacy to be an important element of patient focused drug development and seeks opportunities to collaborate with patient advocacy groups throughout the discovery and development process. The Company’s current clinical program for its lead investigational drug product candidate, ELX-02, includes studies in both cystic fibrosis and nephropathic cystinosis. During the quarter ended September 30, 2019, the Company announced that the Cystic Fibrosis Foundation (the “CF Foundation”) is providing funding for a portion of the U.S. Phase 2 cystic fibrosis clinical trial and that it will form a joint program advisory group with the CF Foundation focused on the development of ELX-02 for cystic fibrosis. The Cystic Fibrosis Therapeutics Development Network (“TDN”) has sanctioned the Phase 2 study protocol, which will be conducted at TDN member sites. Liquidity The Company has a history of net losses and negative cash flows from operating activities since inception, and as of September 30, 2019, had an accumulated deficit of $125.4 million. The Company expects to continue to incur net losses and use cash in its operations for the foreseeable future. To date, the Company has not generated revenue from the sale of any product or service and does not expect to generate significant revenue unless and until it obtains marketing approval for and commercializes its product candidates currently in development. Successful transition to profitable operations is dependent upon achieving a level of revenue adequate to support the Company’s cost structure. The Company has financed its operations primarily from the sale of equity securities and to a lesser extent, loans and grants. The Company may never achieve profitability, and unless and until it does, the Company will continue to need to raise additional capital to fund its operations. The Company believes that its cash, cash equivalents and marketable securities of $64.9 million at September 30, 2019 will enable it to meet anticipated cash needs required to reach top line Phase 2 data in cystic fibrosis and in cystinosis and maintain the Company’s current and planned operations into the first quarter of 2021.

Summary of Significant Accounti

Summary of Significant Accounting Policies	9 Months Ended
	Sep. 30, 2019
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	2. Summary of Significant Accounting Policies Basis of presentation and principles of consolidation The accompanying unaudited interim consolidated financial statements have been prepared by the Company in accordance with accounting principles generally accepted in the United States of America (“U.S. GAAP”) as found in the Accounting Standards Codification (“ASC”) and Accounting Standards Updates (“ASUs”) of the Financial Accounting Standards Board (“FASB”). Certain information and footnote disclosures normally included in the Company’s annual financial statements have been condensed or omitted, as permitted by such rules and regulations. These interim consolidated financial statements, in the opinion of management, reflect all normal recurring adjustments necessary for a fair presentation of the Company’s financial position, results of operations, and cash flows for the interim periods ended September 30, 2019 and 2018. The unaudited Condensed Consolidated Statements of Operations include the Company’s operating expenses related to research and development and general and administrative activities which were substantially comprised of fees for professional services and employee compensation. The results of operations for the interim periods are not necessarily indicative of the results of operations to be expected for the full year. These interim financial statements should be read in conjunction with the audited financial statements as of and for the year ended December 31, 2018, and the notes thereto, which are included in the Company’s Annual Report on Form 10-K filed with the Securities and Exchange Commission (the “SEC”) on March 14, 2019. Summary of Accounting Policies The significant accounting policies and estimates used in the preparation of the condensed consolidated financial statements are described in the Company’s audited financial statements as of and for the year ended December 31, 2018, and the notes thereto, which are included in the Company’s Annual Report on Form 10-K. During the nine months ended September 30, 2019, the Company invested in marketable securities and as a result has provided the following update. Marketable Securities —All investment instruments with an original maturity date, when purchased, in excess of three months but less than 1 year have been classified as current marketable securities. The Company classifies securities that are available to fund current operations as current assets. These marketable securities are classified as available-for-sale and are carried at fair value. The Company records unrealized gains and losses on available-for-sale debt securities as a component of accumulated other comprehensive income, which is a separate component of stockholders’ equity on its condensed consolidated balance sheet, until such gains and losses are realized. Realized gains and losses on available-for-sale securities are included in interest income. The cost of securities sold is based on the specific identification method. The Company periodically reviews the portfolio of securities to determine whether an other-than-temporary impairment has occurred. No such losses have occurred to date. There were no realized gains or losses on the sale of securities for the three and nine months ended September 30, 2019 . Below is a summary of cash, cash equivalents and marketable securities at September 30, 2019 (in thousands): Amortized Unrealized Unrealized Fair Cost Gains Losses Value Cash and cash equivalents $ 22,155 $ — $ — $ 22,155 Marketable securities - U.S. treasuries 42,769 15 (3 ) 42,781 Total cash, cash equivalents and marketable securities $ 64,924 $ 15 $ (3 ) $ 64,936 Fair Value Measurements —Fair value is determined based on the exchange price that would be received for an asset or paid to transfer a liability (an exit price) in the principal market for the asset or liability in an orderly transaction between market participants. Authoritative guidance specifies a hierarchy of valuation techniques based upon whether the inputs to those valuation techniques reflect assumptions other market participants would use based upon market data obtained from independent sources (observable inputs) or reflect the Company’s own assumptions of market participant valuation (unobservable inputs). The fair value hierarchy consists of three levels: Level 1 - Quoted prices (“unadjusted”) in active markets that are unadjusted and accessible at the measurement date for identical, unrestricted assets or liabilities. Level 2 - Observable inputs other than Level 1 prices, such as quoted prices for similar assets or liabilities, quoted prices in markets that are not active, or inputs that are observable or can be corroborated by observable market data for substantially the full term of the assets or liabilities. Level 3 - Unobservable inputs that are supported by little or no market activity and that are significant to the fair value of the assets or liabilities. Financial assets and liabilities are classified within the fair value hierarchy based on the lowest level of input that is significant to the fair value measurement. The authoritative guidance requires the use of observable market data if such data is available without undue cost and effort. When available, the Company uses unadjusted quoted market prices to measure fair value and classify such items within Level 1. If quoted market prices are not available, fair value is based upon internally developed models that use, where possible, current market-based or independently-sourced market parameters, such as interest and currency rates and comparable transactions. Items valued using internally generated models are classified according to the lowest level input or value driver that is significant to the valuation. Thus, items may be classified in Level 3 even though there may be inputs that are readily observable. If quoted market prices are not available, the valuation model used generally depends on the specific asset or liability being valued. At September 30, 2019, the Company’s financial assets valued based on Level 1 inputs consisted of cash, cash equivalents and marketable securities (U.S. treasuries). During the three and nine months ended September 30, 2019 Some assets and liabilities are required to be recorded at fair value on a recurring basis, while other assets and liabilities are recorded at fair value on a nonrecurring basis. The carrying amounts of current financial instruments, which include accounts payable, accrued expenses, lease obligation liability and debt, approximate their fair values due to the short-term nature of these instruments. Concentrations of Credit Risk and Off-Balance-Sheet Risk —Financial instruments that potentially subject the Company to credit risk primarily consist of cash and cash equivalents and available-for-sale marketable securities. The Company mitigates its risk with respect to cash and cash equivalents and marketable securities by maintaining its deposits and investments at high-quality financial institutions. The Company invests any excess cash in money market funds and other securities, and the management of these investments is not discretionary on the part of the financial institution. The Company has no significant off-balance-sheet risks such as foreign exchange contracts, option contracts, or other hedging arrangements. Recent Accounting Pronouncements – Adopted In February 2016, the FASB issued ASU 2016-02, Leases Leases Recent Accounting Pronouncements – Pending Adoption In June 2016, the FASB issued ASU 2016-13, Measurement of Credit Losses on Financial Instruments In August 2018, the FASB issued ASU 2018-13, Fair Value Measurement (Topic 820): Disclosure Framework-Changes to the Disclosure Requirements for Fair Value Measurement

Prepaid Expenses and Other Curr

Prepaid Expenses and Other Current Assets	9 Months Ended
	Sep. 30, 2019
Prepaid And Other Current Assets [Abstract]
Prepaid Expenses and Other Current Assets	3. Prepaid Expenses and Other Current Assets Prepaid expenses and other current assets as of September 30, 2019 and December 31, 2018 consisted of the following (in thousands): As of September 30, 2019 December 31, 2018 Prepaid research and development $ 667 $ 864 Prepaid other 533 555 Other receivable 403 — Prepaid insurance 269 251 Other governmental agencies receivables 6 20 $ 1,878 $ 1,690

Property and Equipment

Property and Equipment	9 Months Ended
	Sep. 30, 2019
Property Plant And Equipment [Abstract]
Property and Equipment	4. Property and Equipment Property and equipment as of September 30, 2019 and December 31, 2018 consisted of the following (in thousands): As of September 30, 2019 December 31, 2018 Computers and software $ 170 $ 146 Office furniture and equipment 164 165 Leasehold improvements 158 141 492 452 Less: Accumulated depreciation (272 ) (204 ) Property and equipment, net $ 220 $ 248 Depreciation expense was $18 thousand and $75 thousand for the three months ended September 30, 2019 and 2018 and $68 thousand and $121 thousand for the nine months ended September 30, 2019 and 2018, respectively.

Accrued Expenses

Accrued Expenses	9 Months Ended
	Sep. 30, 2019
Payables And Accruals [Abstract]
Accrued Expenses	5. Accrued Expenses Accrued expenses as of September 30, 2019 and December 31, 2018 consisted of the following (in thousands): As of September 30, 2019 December 31, 2018 Research and development expenses $ 2,032 $ 3,086 Payroll, bonus and other employee-related expenses 1,983 2,562 Professional services 801 985 Accrued other 233 305 Accrued interest on debt 96 — $ 5,145 $ 6,938

Leases

Leases	9 Months Ended
	Sep. 30, 2019
Leases [Abstract]
Leases	6. Leases The Company adopted the new lease accounting standard, Topic 842, effective January 1, 2019. The Company has elected the ‘package of practical expedients’, which permits it not to reassess under the new standard its prior conclusions about lease identification, lease classification and initial direct costs. In addition, the Company elected not to apply Topic 842 to arrangements with lease terms of 12 months or less. The Company has operating leases for its principal offices in the U.S. and Israel. Operating lease assets represent the Company’s right to use an underlying asset for the lease term and operating lease liabilities represent the Company’s obligation to make lease payments arising from its operating leases. In determining the length of the lease term to its long-term lease, the Company determined not to consider an embedded renewal option for one operating lease primarily due to i) the renewal rate is at future market rate to be determined and ii) Company does not have significant leasehold improvements that would restrict its ability to consider relocation. The Company applied its incremental borrowing rate based upon information available in determining the present value of the lease payments. The Company’s incremental borrowing rate is determined using a secured borrowing rate for the same currency and term as the associated lease. Operating lease costs under the leases for the three and nine months ended September 30, 2019 were approximately $0.1 million and $0.4 million, respectively. Lease expense for these leases is recognized on a straight-line basis over the lease term, with variable lease payments recognized in the period those payments are incurred. At lease commencement date, the Company estimated the lease liability and the right-of-use assets at present value using the Company’s estimated incremental borrowing rate of 8% and determined the initial present value, at inception, of $1.5 million. On January 1, 2019, upon adoption of Topic 842, the Company recorded right-of-use assets of $1.2 million and lease liabilities of $1.2 The following table summarizes the Company’s maturities of operating lease liabilities as of September 30, 2019 (in thousands): Remainder of 2019 $ 138 2020 493 2021 310 Total lease payments 941 Less: present value discount (71 ) Total $ 870 For comparative purposes, the Company’s aggregate future minimum non-cancellable commitments under operating leases as of December 31, 2018 were as follows (in thousands): 2019 $ 541 2020 490 2021 310 Total minimum lease payments $ 1,341

Debt

Debt	9 Months Ended
	Sep. 30, 2019
Debt Disclosure [Abstract]
Debt	7. Debt On January 30, 2019, the Company entered into a Loan and Security Agreement (the “SVB Loan Agreement”) with Silicon Valley Bank (“SVB”) and WestRiver Innovation Lending Fund VIII, L.P. (“WestRiver”, and together with SVB, the “Lenders”). Under the SVB Loan Agreement, the Lenders agreed to extend term loans to the Company in an aggregate principal amount of $25.0 million, comprised of (i) an initial loan advance of $15.0 million; and (ii) a subsequent loan advance of $10.0 million, subject to first achieving certain conditions (collectively, the “Term Loan Advances”). The initial term loan was funded on January 30, 2019. The subsequent term loan advance is available until December 31, 2019 at the Company’s election after the occurrence of certain milestone events relating to data from the Company’s clinical trials and receipt by the Company of certain minimum cash proceeds of at least $75 million from an additional equity offering through a private placement or a public offering. Any outstanding principal on the Term Loan Advances will accrue interest at a floating rate equal to the greater of (i) 5.25% per annum and (i) the sum of 2.5% plus the prime rate, as published in the Wall Street Journal. Interest payments are payable monthly following the funding of a Term Loan advance. On September 30, 2019, the rate was 7.65%. The Company will be required to make principal payments on the outstanding balance of the Term Loan Advances commencing on February 1, 2020 (the “Term Loan Amortization Date”) in 36 equal monthly installments, plus interest; provided that if the Company has achieved the milestones described above relating to the availability of the subsequent loan advance on or prior to December 31, 2019, then the Term Loan Amortization Date is automatically extended to February 1, 2021. Any amounts outstanding under the Term Loan Advances, if not repaid sooner, are due and payable on January 1, 2023 (the “Maturity Date”). In conjunction with the initial loan advance, the Company issued warrants (the “Warrants”) to SVB and WestRiver to purchase an aggregate of 40,834 shares of the Company’s common stock at a warrant exercise price of $11.02 (subject to certain adjustments), which price was calculated using the 10-day average bid price of the Company’s common stock prior to the date of the SVB Loan Agreement. If the subsequent term loan is advanced, the Company will be obligated to issue Warrants to the Lender to purchase an aggregate of 27,222 shares of the Company’s common stock. The Company may prepay the outstanding principal balance of the term loans advanced by SVB in whole but not in part, subject to a prepayment fee ranging from 1% to 3% of any amount prepaid, depending upon when the prepayment occurs. The Company will also pay a final payment fee equal to 6% of the total term loans advanced, due upon the earliest of maturity or termination of the SVB Loan Agreement. Under the terms of the SVB Loan Agreement, the Company granted first priority liens and security interests in substantially all of the Company’s assets (excluding all of its intellectual property, which is subject to a negative pledge) and a pledge by the Company of the shares of one of its wholly-owned subsidiaries as collateral for the obligations thereunder. The SVB Loan Agreement also contains representations and warranties by the Company and SVB and indemnification provisions in favor of SVB and customary covenants (including limitations on other indebtedness, liens, acquisitions, investments and dividends, but no financial covenants), and events of default (including payment defaults, breaches of covenants following any applicable cure period, a material impairment in the perfection or priority of SVB’s security interest in the collateral, and events relating to bankruptcy or insolvency). As of September 30, 2019, the carrying value of the term loan consists of $15.0 million principal outstanding less the unamortized debt issuance costs of approximately $1.2 million. The debt issuance costs have been recorded as a debt discount which are being accreted to interest expense through the maturity date of the term loan. Interest expense relating to the term loan for the three and nine months ended September 30, 2019 was $0.4 million and $1.2 million, respectively. Interest expense is calculated using the effective interest method and is inclusive of non-cash amortization of capitalized loan costs. At September 30, 2019, the effective interest rate was 12.65%. The final maturity payment of $0.9 million is recognized over the life of the term loan through interest expense using the effective interest method. The Company’s scheduled future principal payments for the long-term debt are as follows (in thousands): September 30, 2019 Remainder of 2019 $ — 2020 4,583 2021 5,000 2022 5,000 2023 417 Total future principal payments 15,000 Less: unamortized discount (1,219 ) Carrying value of long-term debt 13,781 Less: current portion (3,488 ) Add: Final fee due at maturity in 2023 900 Long-term portion $ 11,193

Legal and Other Contingencies

Legal and Other Contingencies	9 Months Ended
	Sep. 30, 2019
Commitments And Contingencies Disclosure [Abstract]
Legal and Other Contingencies	8. Legal and Other Contingencies From time to time, the Company may become involved in various lawsuits and legal proceedings, which arise in the ordinary course of business. The Company is currently unaware of any material pending legal proceedings to which it is a party or of which its property is the subject. However, the Company may at times in the future become involved in litigation in the ordinary course of business, which may include actions related to or based on its intellectual property and its use, customer claims, employment practices and employee complaints and other events arising out of its operations. When appropriate in management’s estimation, the Company will record adequate reserves in its financial statements for pending litigation. Litigation is subject to inherent uncertainties, and an adverse result in any such matters could adversely impact its reputation, operations, and its financial operating results or overall financial condition. Additionally, any litigation to which the Company may become subject could also require significant involvement of its senior management and may divert management’s attention from its business and operations. The Company accounts for its contingent liabilities in accordance with ASC Topic 450, “Contingencies”. A provision is recorded when it is both probable that a liability has been incurred and the amount of the loss can be reasonably estimated. With respect to legal matters, provisions are reviewed and adjusted to reflect the impact of negotiations, estimated settlements, legal rulings, advice of legal counsel and other information and events pertaining to a particular matter. For the periods ended September 30, 2019 and 2018, the Company was not a party to any litigation that is reasonably possible to have a material adverse effect on the Company’s business, financial position, results of operations or cash flows. Legal costs incurred in connection with loss contingencies are expensed as incurred. During the quarter ended September 30, 2019, the Company received a funding award from the CF Foundation and entered into an agreement relating to the award and provision of other services. Payment of award amounts are subject to achievement of certain milestones in connection with the Company’s cystic fibrosis development program in the U.S. The funding provided to the Company is accounted for as an advance from a collaboration partner within the scope of ASC Topic 730, “Research and Development.” The Company recorded a liability for advances from collaboration partners of $0.4 million as of September 30, 2019.

Stockholders' Equity

Stockholders' Equity	9 Months Ended
	Sep. 30, 2019
Equity [Abstract]
Stockholders' Equity	9. Stockholders’ Equity For accounting purposes, all common stock, preferred stock, warrants, options to purchase common stock and loss per share amounts have been adjusted to give retroactive effect to the exchange ratio and reverse stock split for all periods presented in these condensed unaudited consolidated financial statements. On April 30, 2018, the Company completed an underwritten public offering of 5,899,500 shares of common stock at the public offering price of $9.75 per share and received net proceeds of approximately $53.6 million after deducting underwriting discounts and commissions and estimated offering expenses. On June 24, 2019, the Company completed an underwritten public offering of 3,833,334 shares of common stock of the Company at the public offering price of $9.00 per share and received net proceeds of approximately $32.2 million after deducting underwriting discounts and commissions of $2.1 million and estimated offering expenses of $0.2 million. Transactions related to stockholders’ equity of the Company during the three and nine months ended September 30, 2019 were as follows (in thousands, except share data): Common stock Treasury stock Shares Amount Additional Paid-in Capital Accumulated Other Comprehensive Income Accumulated deficit Shares Amount Total stockholders' equity Balance at December 31, 2018 35,860,114 $ 360 $ 129,825 $ — $ (86,145 ) (91,423 ) $ (1,129 ) $ 42,911 Exercise of stock options 25,000 — 25 — — — — 25 Vesting of restricted stock units 25,132 — — — — (10,467 ) (121 ) (121 ) Issuance of shares from at-the- market sales agreement 35,362 1 454 — — — — 455 Issuance of warrants — — 421 — — — — 421 Stock-based compensation — — 2,658 — — — — 2,658 Change in unrealized gain (loss) on investments — — — 1 — — — 1 Net loss — — — — (11,917 ) — — (11,917 ) Balance at March 31, 2019 35,945,608 $ 361 $ 133,383 $ 1 $ (98,062 ) (101,890 ) $ (1,250 ) $ 34,433 Exercise of stock options 36,790 — 90 — — — — 90 Issuance of shares upon exercise of warrants 44,814 — 178 — — (14,893 ) (178 ) — Vesting of restricted stock units 54,122 3 (3 ) — — (11,914 ) (111 ) (111 ) Issuance of shares upon equity financing, net of the underwriting discounts and commissions and offering expenses 3,833,334 38 32,184 — — — — 32,222 Stock-based compensation — — 3,016 — — — — 3,016 Change in unrealized gain (loss) on investments — — — 23 — — — 23 Net loss — — — — (14,449 ) — — (14,449 ) Balance at June 30, 2019 39,914,668 $ 402 $ 168,848 $ 24 $ (112,511 ) (128,697 ) $ (1,539 ) $ 55,224 Exercise of stock options 29,537 — 28 — — — — 28 Vesting of restricted stock units 33,449 2 — — — (10,835 ) (46 ) (44 ) Equity financing issuance costs — — (50 ) — — — — (50 ) Stock-based compensation — — 2,957 — — — — 2,957 Change in unrealized gain (loss) on investments — — — (12 ) — — — (12 ) Net loss — — — — (12,875 ) — — (12,875 ) Balance at September 30, 2019 39,977,654 $ 404 $ 171,783 $ 12 $ (125,386 ) (139,532 ) $ (1,585 ) $ 45,228 Transactions related to stockholders’ equity of the Company during the three and nine months ended September 30, 2018 were as follows (in thousands, except share data): Common stock Treasury stock Shares Amount Additional Paid-in Capital Accumulated deficit Shares Amount Total stockholders' equity Balance at December 31, 2017 27,527,738 $ 274 $ 60,047 $ (38,960 ) — $ — $ 21,361 Stock-based compensation — — 735 — — — 735 Net loss — — — (8,591 ) — — (8,591 ) Balance at March 31, 2018 27,527,738 $ 274 $ 60,782 $ (47,551 ) — $ — $ 13,505 Exercise of stock options 808,443 8 89 — — — 97 Issuance of shares upon Technion settlement 569,395 6 (6 ) — — — — Issuance of shares upon execution of warrants 60,989 1 51 — (3,385 ) (52 ) — Issuance of shares upon public offering 5,899,500 60 53,513 — — 53,573 Repurchase of common shares (5,076 ) — — — (5,000 ) (31 ) (31 ) Stock-based compensation — — 6,178 — — — 6,178 Net loss — — — (13,406 ) — — (13,406 ) Balance at June 30, 2018 34,860,989 $ 349 $ 120,607 $ (60,957 ) (8,385 ) $ (83 ) $ 59,916 Exercise of stock options 255,394 2 4 — — — 6 Issuance of shares upon execution of warrants 3,385 — — — — — — Repurchase of common shares 5,076 — — — — — — Stock-based compensation — — 2,695 — — — 2,695 Net loss — — — (11,161 ) — — (11,161 ) Balance at September 30, 2018 35,124,844 $ 351 $ 123,306 $ (72,118 ) (8,385 ) $ (83 ) $ 51,456 Warrants In connection with the January 2019 issuance of debt, the Company granted 40,834 warrants to purchase 40,834 shares of common stock and recorded a charge in additional paid-in-capital in the amount of $0.4 million reflecting the fair value of the warrants on the date of issuance. During the six months ended June 30, 2019, a warrant holder exercised their warrant for a total of 59,707 shares at a weighted average exercise price of $3.01 per share. This exercise has been recorded on a non-cash basis net of shares held as treasury stock. No warrants were granted, exercised or forfeited during the three months ended September 30, 2019. Transactions related to warrants to purchase the Company’s common stock during the nine months ended September 30, 2019, were as follows: Shares Weighted average exercise price Weighted average remaining contractual life Warrants outstanding and exercisable at December 31, 2018 347,241 $ 3.77 3.92 Granted 40,834 11.02 10.00 Exercised (59,707 ) 3.01 — Forfeited (4,474 ) 40.00 — Warrants outstanding and exercisable at September 30, 2019 323,894 $ 4.32 3.99

Stock-Based Compensation

Stock-Based Compensation	9 Months Ended
	Sep. 30, 2019
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Stock-Based Compensation	10. Stock-Based Compensation Stock Incentive Plans On March 12, 2018, the Company’s Board of Directors (the “Board”) adopted the 2018 Equity Incentive Plan (the “2018 Plan”). The 2018 Plan became effective on April 20, 2018 upon approval by the stockholders of the Company with the outstanding options and shares available for future grant under the Sevion 2008 Incentive Compensation Plan (the “2008 Plan”) and the Eloxx Limited 2013 Share Ownership and Option Plan (the “2013 Plan”) being assumed by the 2018 Plan and the total number of shares available for awards to employees, non-employee directors and other key personnel increased by 5,000,000 shares. Upon the 2018 Plan becoming effective, the Company ceased granting awards under each of the 2008 Plan and the 2013 Plan. Stock options granted have a ten-year contractual life and, upon termination, vested options are generally exercisable between one and three months following the termination date, while unvested options are forfeited immediately. Summary of Option Activity Transactions related to the grant of stock options to employees and directors during the nine months ended September 30, 2019 were as follows: Shares Weighted average exercise price Weighted average remaining contractual life Aggregate intrinsic value Options outstanding at December 31, 2018 3,261,719 $ 13.09 8.56 $ 11,650,373 Granted 1,780,200 9.43 Exercised (91,327 ) 12.98 Forfeited (153,552 ) 12.76 Options outstanding at September 30, 2019 4,797,040 $ 11.96 8.54 $ 1,121,950 Options exercisable at September 30, 2019 1,730,606 $ 13.69 7.55 $ 1,024,195 The aggregate intrinsic value represents the total intrinsic value (the difference between the deemed fair value of the Company’s common stock as of September 30, 2019 and the exercise price, multiplied by the number of in-the-money options) that would have been received by the option holders had all option holders exercised their options on September 30, 2019. This amount is impacted by the changes in the fair value of the Company’s common stock. Summary of Restricted Stock Unit Activity Transactions related to the grant of restricted stock units to employees and directors during the nine months ended September 30, 2019 were as follows: Shares Weighted average grant date fair value price Unvested at December 31, 2018 554,147 $ 9.34 Granted 100,000 11.53 Vested (145,919 ) 9.90 Forfeited — — Unvested at September 30, 2019 508,228 $ 9.61 In December 2017, the Company issued an inducement award outside of the prior plans to the Company’s Chief Executive Officer in the form of an option to purchase 22,427 shares of the Company’s common stock with an exercise price per share equal to $8.00, and an award of restricted stock units for 22,427 shares of the Company’s common stock (collectively the “Performance Option Awards”). Subject to continued service through the vesting date, the Performance Option Awards will vest and become immediately exercisable upon the date that marks the first successful completion of a Phase2-B study with respect to any indication. For each of the three months ended September 30, 2019 and September 30, 2018, the Company recognized $24 thousand of expense associated with these awards and for each of the nine months ended September 30, 2019 and September 30, 2018, the Company recognized $73 thousand of expense associated with these awards. In addition, in December 2017, the Company issued an inducement award outside of the Stock-based compensation relates to stock options granted to employees, non-employee directors and non-employees, time-based restricted stock units granted to employees and performance-based stock options and restricted stock units granted to an employee. The total equity-based compensation expense related to all of the Company’s equity-based awards were recognized as follows: Three months ended September 30, Nine months ended September 30, 2019 2018 2019 2018 Research and development $ 718 $ 498 $ 1,987 $ 909 General and administrative 2,239 2,197 6,644 8,699 Total stock-based compensation expenses $ 2,957 $ 2,695 $ 8,631 $ 9,608

Other Expense (Income), Net

Other Expense (Income), Net	9 Months Ended
	Sep. 30, 2019
Other Income And Expenses [Abstract]
Other Expense (Income), Net	11. Other Expense (Income), Net Other expense (income), net consisted of the following (in thousands): Three months ended September 30, Nine months ended September 30, 2019 2018 2019 2018 Interest and other income $ (272 ) $ (223 ) $ (766 ) $ (368 ) Investment income, net (92 ) — (224 ) — Interest and other expense 460 24 1,164 75 Total other expense (income), net $ 96 $ (199 ) $ 174 $ (293 )

Net Loss Per Share

Net Loss Per Share	9 Months Ended
	Sep. 30, 2019
Earnings Per Share [Abstract]
Net Loss Per Share	12. Net Loss Per Share The loss and the weighted average number of shares used in computing basic and diluted net loss per share for the periods, is as follows (amounts in thousands, except share data): Three months ended September 30, Nine months ended September 30, 2019 2018 2019 2018 Numerator: Net loss $ (12,875 ) $ (11,161 ) $ (39,241 ) $ (33,158 ) Denominator: Shares used in computing net loss per share of common stock, basic and diluted (1) 39,944,324 35,005,979 37,394,310 31,485,067 Net loss per share of common stock, basic and diluted $ (0.32 ) $ (0.32 ) $ (1.05 ) $ (1.05 ) (1) The following potentially dilutive securities have been excluded from the computation of diluted weighted average shares outstanding as their effect would be anti-dilutive: Nine months ended September 30, 2019 2018 Options to purchase common stock 4,797,040 3,611,400 Restricted stock units 508,228 767,743 Warrants 323,894 347,241 Total potential common stock equivalents 5,629,162 4,726,384

Reverse Merger

Reverse Merger	9 Months Ended
	Sep. 30, 2019
Business Combinations [Abstract]
Reverse Merger	13. Reverse Merger On December 19, 2017, Sevion Therapeutics, Inc. (“Sevion”) acquired Eloxx Pharmaceuticals, Limited (“Eloxx Limited”) pursuant to a merger between the companies (the “Transaction” or “Reverse Merger”). Upon consummation of the Transaction (the “Closing”), Sevion adopted the business plan of Eloxx Limited and discontinued the pursuit of Sevion’s pre-Closing business plan. In connection with the Transaction, Sevion agreed to acquire all of the outstanding capital stock of Eloxx Limited in exchange for the issuance of an aggregate 20,316,656 shares of the Sevion’s common stock, par value $0.01 per share, after giving effect to a 1-for-20 reverse split effected immediately prior to the Transaction. Immediately after giving effect to the Transaction, on December 19, 2017, Sevion changed its name to Eloxx Pharmaceuticals, Inc. The Reverse Merger was accounted for as a reverse recapitalization which is outside the scope of ASC Topic 805, “Business Combinations”. Under reverse capitalization accounting, Eloxx Limited is considered the acquirer for accounting and financial reporting purposes and acquired the assets and assumed the liabilities of the Company. The assets acquired and liabilities assumed are reported at their historical amounts. The annual consolidated financial statements of the Company reflect the operations of the acquirer for accounting purposes together with a deemed issuance of shares, equivalent to the shares held by the former stockholders of the legal acquirer and a recapitalization of the equity of the accounting acquirer. The annual consolidated financial statements include the accounts of the Company since the effective date of the reverse capitalization and the accounts of Eloxx Limited since inception. The following summarizes the estimated fair value of the assets and liabilities assumed at the date of the Reverse Merger (in thousands): December 19, 2017 Cash and cash equivalents $ 123 Prepaid expenses and other current assets 220 Property, plant and equipment, net 39 Restricted bank deposits 6 Total assets acquired 388 Accounts payable (215 ) Accrued expenses (343 ) Total liabilities acquired (558 ) Total net liabilities acquired $ (170 )

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	9 Months Ended
	Sep. 30, 2019
Accounting Policies [Abstract]
Basis of presentation and principles of consolidation	Basis of presentation and principles of consolidation The accompanying unaudited interim consolidated financial statements have been prepared by the Company in accordance with accounting principles generally accepted in the United States of America (“U.S. GAAP”) as found in the Accounting Standards Codification (“ASC”) and Accounting Standards Updates (“ASUs”) of the Financial Accounting Standards Board (“FASB”). Certain information and footnote disclosures normally included in the Company’s annual financial statements have been condensed or omitted, as permitted by such rules and regulations. These interim consolidated financial statements, in the opinion of management, reflect all normal recurring adjustments necessary for a fair presentation of the Company’s financial position, results of operations, and cash flows for the interim periods ended September 30, 2019 and 2018. The unaudited Condensed Consolidated Statements of Operations include the Company’s operating expenses related to research and development and general and administrative activities which were substantially comprised of fees for professional services and employee compensation. The results of operations for the interim periods are not necessarily indicative of the results of operations to be expected for the full year. These interim financial statements should be read in conjunction with the audited financial statements as of and for the year ended December 31, 2018, and the notes thereto, which are included in the Company’s Annual Report on Form 10-K filed with the Securities and Exchange Commission (the “SEC”) on March 14, 2019.
Marketable Securities	Marketable Securities —All investment instruments with an original maturity date, when purchased, in excess of three months but less than 1 year have been classified as current marketable securities. The Company classifies securities that are available to fund current operations as current assets. These marketable securities are classified as available-for-sale and are carried at fair value. The Company records unrealized gains and losses on available-for-sale debt securities as a component of accumulated other comprehensive income, which is a separate component of stockholders’ equity on its condensed consolidated balance sheet, until such gains and losses are realized. Realized gains and losses on available-for-sale securities are included in interest income. The cost of securities sold is based on the specific identification method. The Company periodically reviews the portfolio of securities to determine whether an other-than-temporary impairment has occurred. No such losses have occurred to date. There were no realized gains or losses on the sale of securities for the three and nine months ended September 30, 2019 . Below is a summary of cash, cash equivalents and marketable securities at September 30, 2019 (in thousands): Amortized Unrealized Unrealized Fair Cost Gains Losses Value Cash and cash equivalents $ 22,155 $ — $ — $ 22,155 Marketable securities - U.S. treasuries 42,769 15 (3 ) 42,781 Total cash, cash equivalents and marketable securities $ 64,924 $ 15 $ (3 ) $ 64,936
Fair Value Measurements	Fair Value Measurements —Fair value is determined based on the exchange price that would be received for an asset or paid to transfer a liability (an exit price) in the principal market for the asset or liability in an orderly transaction between market participants. Authoritative guidance specifies a hierarchy of valuation techniques based upon whether the inputs to those valuation techniques reflect assumptions other market participants would use based upon market data obtained from independent sources (observable inputs) or reflect the Company’s own assumptions of market participant valuation (unobservable inputs). The fair value hierarchy consists of three levels: Level 1 - Quoted prices (“unadjusted”) in active markets that are unadjusted and accessible at the measurement date for identical, unrestricted assets or liabilities. Level 2 - Observable inputs other than Level 1 prices, such as quoted prices for similar assets or liabilities, quoted prices in markets that are not active, or inputs that are observable or can be corroborated by observable market data for substantially the full term of the assets or liabilities. Level 3 - Unobservable inputs that are supported by little or no market activity and that are significant to the fair value of the assets or liabilities. Financial assets and liabilities are classified within the fair value hierarchy based on the lowest level of input that is significant to the fair value measurement. The authoritative guidance requires the use of observable market data if such data is available without undue cost and effort. When available, the Company uses unadjusted quoted market prices to measure fair value and classify such items within Level 1. If quoted market prices are not available, fair value is based upon internally developed models that use, where possible, current market-based or independently-sourced market parameters, such as interest and currency rates and comparable transactions. Items valued using internally generated models are classified according to the lowest level input or value driver that is significant to the valuation. Thus, items may be classified in Level 3 even though there may be inputs that are readily observable. If quoted market prices are not available, the valuation model used generally depends on the specific asset or liability being valued. At September 30, 2019, the Company’s financial assets valued based on Level 1 inputs consisted of cash, cash equivalents and marketable securities (U.S. treasuries). During the three and nine months ended September 30, 2019 Some assets and liabilities are required to be recorded at fair value on a recurring basis, while other assets and liabilities are recorded at fair value on a nonrecurring basis. The carrying amounts of current financial instruments, which include accounts payable, accrued expenses, lease obligation liability and debt, approximate their fair values due to the short-term nature of these instruments.
Concentration of Credit Risk and Off-Balance-Sheet Risk	Concentrations of Credit Risk and Off-Balance-Sheet Risk —Financial instruments that potentially subject the Company to credit risk primarily consist of cash and cash equivalents and available-for-sale marketable securities. The Company mitigates its risk with respect to cash and cash equivalents and marketable securities by maintaining its deposits and investments at high-quality financial institutions. The Company invests any excess cash in money market funds and other securities, and the management of these investments is not discretionary on the part of the financial institution. The Company has no significant off-balance-sheet risks such as foreign exchange contracts, option contracts, or other hedging arrangements.
Recent Accounting Pronouncements	Recent Accounting Pronouncements – Adopted In February 2016, the FASB issued ASU 2016-02, Leases Leases Recent Accounting Pronouncements – Pending Adoption In June 2016, the FASB issued ASU 2016-13, Measurement of Credit Losses on Financial Instruments In August 2018, the FASB issued ASU 2018-13, Fair Value Measurement (Topic 820): Disclosure Framework-Changes to the Disclosure Requirements for Fair Value Measurement

Summary of Significant Accoun_3

Summary of Significant Accounting Policies (Tables)	9 Months Ended
	Sep. 30, 2019
Accounting Policies [Abstract]
Summary of Cash, Cash Equivalents and Marketable Securities	Below is a summary of cash, cash equivalents and marketable securities at September 30, 2019 (in thousands): Amortized Unrealized Unrealized Fair Cost Gains Losses Value Cash and cash equivalents $ 22,155 $ — $ — $ 22,155 Marketable securities - U.S. treasuries 42,769 15 (3 ) 42,781 Total cash, cash equivalents and marketable securities $ 64,924 $ 15 $ (3 ) $ 64,936

Prepaid Expenses and Other Cu_2

Prepaid Expenses and Other Current Assets (Tables)	9 Months Ended
	Sep. 30, 2019
Prepaid And Other Current Assets [Abstract]
Prepaid Expenses and Other Current Assets	Prepaid expenses and other current assets as of September 30, 2019 and December 31, 2018 consisted of the following (in thousands): As of September 30, 2019 December 31, 2018 Prepaid research and development $ 667 $ 864 Prepaid other 533 555 Other receivable 403 — Prepaid insurance 269 251 Other governmental agencies receivables 6 20 $ 1,878 $ 1,690

Property and Equipment (Tables)

Property and Equipment (Tables)	9 Months Ended
	Sep. 30, 2019
Property Plant And Equipment [Abstract]
Property and equipment	Property and equipment as of September 30, 2019 and December 31, 2018 consisted of the following (in thousands): As of September 30, 2019 December 31, 2018 Computers and software $ 170 $ 146 Office furniture and equipment 164 165 Leasehold improvements 158 141 492 452 Less: Accumulated depreciation (272 ) (204 ) Property and equipment, net $ 220 $ 248

Accrued Expenses (Tables)

Accrued Expenses (Tables)	9 Months Ended
	Sep. 30, 2019
Payables And Accruals [Abstract]
Accrued expenses	Accrued expenses as of September 30, 2019 and December 31, 2018 consisted of the following (in thousands): As of September 30, 2019 December 31, 2018 Research and development expenses $ 2,032 $ 3,086 Payroll, bonus and other employee-related expenses 1,983 2,562 Professional services 801 985 Accrued other 233 305 Accrued interest on debt 96 — $ 5,145 $ 6,938

Leases (Tables)

Leases (Tables)	9 Months Ended
	Sep. 30, 2019
Leases [Abstract]
Summary of Maturities of Operating Lease Liabilities	The following table summarizes the Company’s maturities of operating lease liabilities as of September 30, 2019 (in thousands): Remainder of 2019 $ 138 2020 493 2021 310 Total lease payments 941 Less: present value discount (71 ) Total $ 870
Summary of Future Minimum Non-Cancellable Commitments Under Operating Leases	For comparative purposes, the Company’s aggregate future minimum non-cancellable commitments under operating leases as of December 31, 2018 were as follows (in thousands): 2019 $ 541 2020 490 2021 310 Total minimum lease payments $ 1,341

Debt (Tables)

Debt (Tables)	9 Months Ended
	Sep. 30, 2019
Debt Disclosure [Abstract]
Schedule of Future Principal Payments for Long-Term Debt	The Company’s scheduled future principal payments for the long-term debt are as follows (in thousands): September 30, 2019 Remainder of 2019 $ — 2020 4,583 2021 5,000 2022 5,000 2023 417 Total future principal payments 15,000 Less: unamortized discount (1,219 ) Carrying value of long-term debt 13,781 Less: current portion (3,488 ) Add: Final fee due at maturity in 2023 900 Long-term portion $ 11,193

Stockholders' Equity (Tables)

Stockholders' Equity (Tables)	9 Months Ended
	Sep. 30, 2019
Equity [Abstract]
Schedule of Transactions Related to Stockholders Equity	Transactions related to stockholders’ equity of the Company during the three and nine months ended September 30, 2019 were as follows (in thousands, except share data): Common stock Treasury stock Shares Amount Additional Paid-in Capital Accumulated Other Comprehensive Income Accumulated deficit Shares Amount Total stockholders' equity Balance at December 31, 2018 35,860,114 $ 360 $ 129,825 $ — $ (86,145 ) (91,423 ) $ (1,129 ) $ 42,911 Exercise of stock options 25,000 — 25 — — — — 25 Vesting of restricted stock units 25,132 — — — — (10,467 ) (121 ) (121 ) Issuance of shares from at-the- market sales agreement 35,362 1 454 — — — — 455 Issuance of warrants — — 421 — — — — 421 Stock-based compensation — — 2,658 — — — — 2,658 Change in unrealized gain (loss) on investments — — — 1 — — — 1 Net loss — — — — (11,917 ) — — (11,917 ) Balance at March 31, 2019 35,945,608 $ 361 $ 133,383 $ 1 $ (98,062 ) (101,890 ) $ (1,250 ) $ 34,433 Exercise of stock options 36,790 — 90 — — — — 90 Issuance of shares upon exercise of warrants 44,814 — 178 — — (14,893 ) (178 ) — Vesting of restricted stock units 54,122 3 (3 ) — — (11,914 ) (111 ) (111 ) Issuance of shares upon equity financing, net of the underwriting discounts and commissions and offering expenses 3,833,334 38 32,184 — — — — 32,222 Stock-based compensation — — 3,016 — — — — 3,016 Change in unrealized gain (loss) on investments — — — 23 — — — 23 Net loss — — — — (14,449 ) — — (14,449 ) Balance at June 30, 2019 39,914,668 $ 402 $ 168,848 $ 24 $ (112,511 ) (128,697 ) $ (1,539 ) $ 55,224 Exercise of stock options 29,537 — 28 — — — — 28 Vesting of restricted stock units 33,449 2 — — — (10,835 ) (46 ) (44 ) Equity financing issuance costs — — (50 ) — — — — (50 ) Stock-based compensation — — 2,957 — — — — 2,957 Change in unrealized gain (loss) on investments — — — (12 ) — — — (12 ) Net loss — — — — (12,875 ) — — (12,875 ) Balance at September 30, 2019 39,977,654 $ 404 $ 171,783 $ 12 $ (125,386 ) (139,532 ) $ (1,585 ) $ 45,228 Transactions related to stockholders’ equity of the Company during the three and nine months ended September 30, 2018 were as follows (in thousands, except share data): Common stock Treasury stock Shares Amount Additional Paid-in Capital Accumulated deficit Shares Amount Total stockholders' equity Balance at December 31, 2017 27,527,738 $ 274 $ 60,047 $ (38,960 ) — $ — $ 21,361 Stock-based compensation — — 735 — — — 735 Net loss — — — (8,591 ) — — (8,591 ) Balance at March 31, 2018 27,527,738 $ 274 $ 60,782 $ (47,551 ) — $ — $ 13,505 Exercise of stock options 808,443 8 89 — — — 97 Issuance of shares upon Technion settlement 569,395 6 (6 ) — — — — Issuance of shares upon execution of warrants 60,989 1 51 — (3,385 ) (52 ) — Issuance of shares upon public offering 5,899,500 60 53,513 — — 53,573 Repurchase of common shares (5,076 ) — — — (5,000 ) (31 ) (31 ) Stock-based compensation — — 6,178 — — — 6,178 Net loss — — — (13,406 ) — — (13,406 ) Balance at June 30, 2018 34,860,989 $ 349 $ 120,607 $ (60,957 ) (8,385 ) $ (83 ) $ 59,916 Exercise of stock options 255,394 2 4 — — — 6 Issuance of shares upon execution of warrants 3,385 — — — — — — Repurchase of common shares 5,076 — — — — — — Stock-based compensation — — 2,695 — — — 2,695 Net loss — — — (11,161 ) — — (11,161 ) Balance at September 30, 2018 35,124,844 $ 351 $ 123,306 $ (72,118 ) (8,385 ) $ (83 ) $ 51,456
Summary of Warrants Outstanding	Transactions related to warrants to purchase the Company’s common stock during the nine months ended September 30, 2019, were as follows: Shares Weighted average exercise price Weighted average remaining contractual life Warrants outstanding and exercisable at December 31, 2018 347,241 $ 3.77 3.92 Granted 40,834 11.02 10.00 Exercised (59,707 ) 3.01 — Forfeited (4,474 ) 40.00 — Warrants outstanding and exercisable at September 30, 2019 323,894 $ 4.32 3.99

Stock-Based Compensation (Table

Stock-Based Compensation (Tables)	9 Months Ended
	Sep. 30, 2019
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Transactions Related to Grant of Stock Options to Employees and Directors	Transactions related to the grant of stock options to employees and directors during the nine months ended September 30, 2019 were as follows: Shares Weighted average exercise price Weighted average remaining contractual life Aggregate intrinsic value Options outstanding at December 31, 2018 3,261,719 $ 13.09 8.56 $ 11,650,373 Granted 1,780,200 9.43 Exercised (91,327 ) 12.98 Forfeited (153,552 ) 12.76 Options outstanding at September 30, 2019 4,797,040 $ 11.96 8.54 $ 1,121,950 Options exercisable at September 30, 2019 1,730,606 $ 13.69 7.55 $ 1,024,195
Transactions Related to Grant of Restricted Stock Units to Employees and Directors	Transactions related to the grant of restricted stock units to employees and directors during the nine months ended September 30, 2019 were as follows: Shares Weighted average grant date fair value price Unvested at December 31, 2018 554,147 $ 9.34 Granted 100,000 11.53 Vested (145,919 ) 9.90 Forfeited — — Unvested at September 30, 2019 508,228 $ 9.61
Summary of Allocated Stock-based Compensation Expense	The total equity-based compensation expense related to all of the Company’s equity-based awards were recognized as follows: Three months ended September 30, Nine months ended September 30, 2019 2018 2019 2018 Research and development $ 718 $ 498 $ 1,987 $ 909 General and administrative 2,239 2,197 6,644 8,699 Total stock-based compensation expenses $ 2,957 $ 2,695 $ 8,631 $ 9,608

Other Expense (Income), Net (Ta

Other Expense (Income), Net (Tables)	9 Months Ended
	Sep. 30, 2019
Other Income And Expenses [Abstract]
Schedule of Other Expense (Income), Net	Other expense (income), net consisted of the following (in thousands): Three months ended September 30, Nine months ended September 30, 2019 2018 2019 2018 Interest and other income $ (272 ) $ (223 ) $ (766 ) $ (368 ) Investment income, net (92 ) — (224 ) — Interest and other expense 460 24 1,164 75 Total other expense (income), net $ 96 $ (199 ) $ 174 $ (293 )

Net Loss Per Share (Tables)

Net Loss Per Share (Tables)	9 Months Ended
	Sep. 30, 2019
Earnings Per Share [Abstract]
Schedule of Loss and Weighted Average Number of Shares Used in Computing Basic and Diluted Net Loss Per Share	The loss and the weighted average number of shares used in computing basic and diluted net loss per share for the periods, is as follows (amounts in thousands, except share data): Three months ended September 30, Nine months ended September 30, 2019 2018 2019 2018 Numerator: Net loss $ (12,875 ) $ (11,161 ) $ (39,241 ) $ (33,158 ) Denominator: Shares used in computing net loss per share of common stock, basic and diluted (1) 39,944,324 35,005,979 37,394,310 31,485,067 Net loss per share of common stock, basic and diluted $ (0.32 ) $ (0.32 ) $ (1.05 ) $ (1.05 ) (1) The following potentially dilutive securities have been excluded from the computation of diluted weighted average shares outstanding as their effect would be anti-dilutive: Nine months ended September 30, 2019 2018 Options to purchase common stock 4,797,040 3,611,400 Restricted stock units 508,228 767,743 Warrants 323,894 347,241 Total potential common stock equivalents 5,629,162 4,726,384

Reverse Merger (Tables)

Reverse Merger (Tables)	9 Months Ended
	Sep. 30, 2019
Eloxx Limited [Member]
Summary of Estimated Fair Value of Assets Acquired and Liabilities Assumed	The following summarizes the estimated fair value of the assets and liabilities assumed at the date of the Reverse Merger (in thousands): December 19, 2017 Cash and cash equivalents $ 123 Prepaid expenses and other current assets 220 Property, plant and equipment, net 39 Restricted bank deposits 6 Total assets acquired 388 Accounts payable (215 ) Accrued expenses (343 ) Total liabilities acquired (558 ) Total net liabilities acquired $ (170 )

Nature of the Business - Additi

Nature of the Business - Additional Information (Detail) $ in Thousands	9 Months Ended
	Sep. 30, 2019USD ($)Disease	Dec. 31, 2018USD ($)
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Number of rare diseases | Disease	1,800
Accumulated deficit	$ (125,386)	$ (86,145)
Cash, cash equivalents and marketable securities	$ 64,936

Summary of Significant Accoun_4

Summary of Significant Accounting Policies - Additional Information (Detail) - USD ($)	3 Months Ended	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2019
Accounting Policies [Abstract]
Realized gains or losses on the sale of securities	$ 0	$ 0
Assets, transfer from level 2 to level 3	$ 0	$ 0

Summary of Significant Accoun_5

Summary of Significant Accounting Policies - Summary of Cash, Cash Equivalents and Marketable Securities (Detail) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018	Sep. 30, 2018
Schedule Of Available For Sale Securities [Line Items]
Cash and cash equivalents	$ 22,155	$ 48,606	$ 55,336
Cash and cash equivalents, Fair Value	22,155
Total cash, cash equivalents and marketable securities, Amortized Cost	64,924
Total cash, cash equivalents and marketable securities, Unrealized Gains	15
Total cash, cash equivalents and marketable securities, Unrealized Losses	(3)
Total cash, cash equivalents and marketable securities, Fair Value	64,936
U.S. treasuries [Member]
Schedule Of Available For Sale Securities [Line Items]
Marketable securities, Amortized Cost	42,769
Marketable securities, Unrealized Gains	15
Marketable securities, Unrealized Losses	(3)
Marketable securities, Fair Value	$ 42,781

Prepaid Expenses and Other Cu_3

Prepaid Expenses and Other Current Assets - Schedule of Prepaid Expenses and Other Current Assets (Detail) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Deferred Costs Capitalized Prepaid And Other Assets Disclosure [Abstract]
Prepaid research and development	$ 667	$ 864
Prepaid other	533	555
Other receivable	403
Prepaid insurance	269	251
Other governmental agencies receivables	6	20
Total	$ 1,878	$ 1,690

Property and Equipment - Proper

Property and Equipment - Property and Equipment (Detail) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Property, Plant and Equipment [Line Items]
Cost	$ 492	$ 452
Less: Accumulated depreciation	(272)	(204)
Property and equipment, net	220	248
Computers and software [Member]
Property, Plant and Equipment [Line Items]
Cost	170	146
Office furniture and equipment [Member]
Property, Plant and Equipment [Line Items]
Cost	164	165
Leasehold improvement [Member]
Property, Plant and Equipment [Line Items]
Cost	$ 158	$ 141

Property and Equipment - Additi

Property and Equipment - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Property Plant And Equipment [Abstract]
Depreciation expenses	$ 18	$ 75	$ 68	$ 121

Accrued Expenses - Accrued Expe

Accrued Expenses - Accrued Expenses (Detail) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Payables And Accruals [Abstract]
Research and development expenses	$ 2,032	$ 3,086
Payroll, bonus and other employee-related expenses	1,983	2,562
Professional services	801	985
Accrued other	233	305
Accrued interest on debt	96
Total	$ 5,145	$ 6,938

Leases - Additional Information

Leases - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2019	Jan. 01, 2019
Leases [Line Items]
Operating lease cost	$ 100	$ 400
Operating lease estimated incremental borrowings rate		8.00%
Operating lease, initial present value	1,500	$ 1,500
Operating lease, right-of-use asset	870	870
Operating lease, liabilities	$ 870	$ 870
Weighted average remaining lease term	1 year 9 months 18 days	1 year 9 months 18 days
ASU 2016-02 [Member]
Leases [Line Items]
Operating lease, right-of-use asset			$ 1,200
Operating lease, liabilities			$ 1,200

Leases - Summary of Maturities

Leases - Summary of Maturities of Operating Lease Liabilities (Details) $ in Thousands	Sep. 30, 2019USD ($)
Leases [Abstract]
Remainder of 2019	$ 138
2020	493
2021	310
Total lease payments	941
Less: present value discount	(71)
Operating lease, liabilities	$ 870

Leases - Summary of Future Mini

Leases - Summary of Future Minimum Non-Cancellable Commitments Under Operating Leases (Detail) $ in Thousands	Dec. 31, 2018USD ($)
Leases [Abstract]
2019	$ 541
2020	490
2021	310
Total minimum lease payments	$ 1,341

Debt - Additional Information (

Debt - Additional Information (Detail) $ / shares in Units, $ in Thousands	Jan. 30, 2019USD ($)Installment$ / sharesshares	Sep. 30, 2019USD ($)$ / sharesshares	Sep. 30, 2019USD ($)$ / sharesshares	Dec. 31, 2018$ / shares
Debt Instrument [Line Items]
Aggregate principal amount of initial loan advance		$ 13,781	$ 13,781
Warrants issued to purchase shares of common stock | shares		40,834	40,834
Warrant exercise price | $ / shares		$ 4.32	$ 4.32	$ 3.77
Term loan, principal outstanding		$ 15,000	$ 15,000
Term loan, final maturity payment		$ 900	$ 900
Loan Agreement [Member]
Debt Instrument [Line Items]
Aggregate principal amount	$ 25,000
Debt instrument, interest rate terms	Any outstanding principal on the Term Loan Advances will accrue interest at a floating rate equal to the greater of (i) 5.25% per annum and (i) the sum of 2.5% plus the prime rate, as published in the Wall Street Journal. Interest payments are payable monthly following the funding of a Term Loan advance.
Debt instrument, payment terms	The Company will be required to make principal payments on the outstanding balance of the Term Loan Advances commencing on February 1, 2020 (the “Term Loan Amortization Date”) in 36 equal monthly installments, plus interest; provided that if the Company has achieved the milestones described above relating to the availability of the subsequent loan advance on or prior to December 31, 2019, then the Term Loan Amortization Date is automatically extended to February 1, 2021.
Term loan, floating interest rate	5.25%
Term loan, interest rate		7.65%	7.65%
Term loan, frequency of periodic payment	monthly
Term loan, number of repayment installments | Installment	36
Term loan, periodic principal payment commencement date	Feb. 1, 2020
Term loan, periodic principal payment, extended commencement date	Feb. 1, 2021
Term loan, maturity date	Jan. 1, 2023
Warrant exercise price | $ / shares	$ 11.02
Common stock average closing bid price number of trading days	10 days
Term loan, final payment fee percentage	6.00%
Term loan, principal outstanding		$ 15,000	$ 15,000
Term loan, unamortized debt issuance costs		1,200	1,200
Term loan, interest expense		$ 400	$ 1,200
Term loan, effective interest rate		12.65%	12.65%
Term loan, final maturity payment		$ 900	$ 900
Loan Agreement [Member] | Prime Rate [Member]
Debt Instrument [Line Items]
Term loan, floating interest rate	2.50%
Loan Agreement [Member] | Minimum [Member]
Debt Instrument [Line Items]
Term loan, prepayment fee percentage	1.00%
Loan Agreement [Member] | Minimum [Member] | Private Placement or Public Offering [Member]
Debt Instrument [Line Items]
Cash proceeds from an additional equity offering	$ 75,000
Loan Agreement [Member] | Maximum [Member]
Debt Instrument [Line Items]
Term loan, prepayment fee percentage	3.00%
Loan Agreement [Member] | Initial Loan [Member]
Debt Instrument [Line Items]
Aggregate principal amount of initial loan advance	$ 15,000
Warrants issued to purchase shares of common stock | shares	40,834
Loan Agreement [Member] | Subsequent Loan [Member]
Debt Instrument [Line Items]
Aggregate principal amount of subsequent loan advance	$ 10,000
Warrants issued to purchase shares of common stock | shares	27,222
Loan Agreement [Member] | Subsequent Loan [Member] | Maximum [Member]
Debt Instrument [Line Items]
Term loan, available date for funding	Dec. 31, 2019

Debt - Schedule of Future Princ

Debt - Schedule of Future Principal Payments for Long-Term Debt (Detail) $ in Thousands	Sep. 30, 2019USD ($)
Debt Disclosure [Abstract]
2020	$ 4,583
2021	5,000
2022	5,000
2023	417
Total future principal payments	15,000
Less: unamortized discount	(1,219)
Carrying value of long-term debt	13,781
Less: current portion	(3,488)
Add: Final fee due at maturity in 2023	900
Long-term debt	$ 11,193

Legal and Other Contingencies -

Legal and Other Contingencies - Additional Information (Detail) $ in Thousands	Sep. 30, 2019USD ($)
Commitments And Contingencies Disclosure [Abstract]
Advances from collaboration partners	$ 403

Stockholder's Equity - Addition

Stockholder's Equity - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands	Jun. 24, 2019	Apr. 30, 2018	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2018	Jun. 30, 2019	Sep. 30, 2019	Sep. 30, 2018
Offering expenses			$ 50
Number of common stock in warrant			40,834					40,834
Warrant granted			0					40,834
Additional paid in capital					$ 421			$ 400
Warrant exercised			0				59,707	59,707
Weighted average exercise price of exercised warrant							$ 3.01	$ 3.01
Warrant forfeited			0					4,474
Underwritten Public Offering [Member]
Net proceeds from common stock shares issued at public offering								$ 32,169	$ 53,573
Underwritten Public Offering [Member] | Common stock [Member]
Common stock, shares issued	3,833,334	5,899,500		3,833,334		5,899,500
Common stock public offering price	$ 9	$ 9.75
Net proceeds from common stock shares issued at public offering	$ 32,200	$ 53,600
Underwriting discounts and commissions	2,100
Offering expenses	$ 200

Stockholder's Equity - Schedule

Stockholder's Equity - Schedule of Transaction Related to Stockholder's Equity (Detail) - USD ($) $ in Thousands	Jun. 24, 2019	Apr. 30, 2018	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Sep. 30, 2019	Sep. 30, 2018
Beginning balance			$ 55,224	$ 34,433	$ 42,911	$ 59,916	$ 13,505	$ 21,361	$ 42,911	$ 21,361
Beginning balance, shares					35,860,114				35,860,114
Exercise of stock options			28	90	$ 25	6	97
Exercise of stock options, shares									91,327
Repurchase of common shares							(31)
Vesting of restricted stock units			(44)	(111)	(121)
Equity financing issuance costs			(50)
Issuance of warrants					421				$ 400
Stock-based compensation			2,957	3,016	2,658	2,695	6,178	735
Change in unrealized gain (loss) on investments			(12)	23	1				12
Net loss			(12,875)	(14,449)	(11,917)	(11,161)	(13,406)	(8,591)	(39,241)	(33,158)
Ending balance			$ 45,228	55,224	34,433	51,456	59,916	13,505	$ 45,228	51,456
Ending balance, shares			39,977,654						39,977,654
At-The-Market Sales Agreement [Member]
Issuance of shares including finance costs					455
Underwritten Public Offering [Member]
Issuance of shares upon equity financing/public offering, net				32,222			53,573
Common stock [Member]
Beginning balance			$ 402	$ 361	$ 360	$ 349	$ 274	$ 274	$ 360	$ 274
Beginning balance, shares			39,914,668	35,945,608	35,860,114	34,860,989	27,527,738	27,527,738	35,860,114	27,527,738
Exercise of stock options						$ 2	$ 8
Exercise of stock options, shares			29,537	36,790	25,000	255,394	808,443
Issuance of shares upon exercise/execution of warrants							$ 1
Issuance of shares upon exercise/execution of warrants, shares				44,814		3,385	60,989
Issuance of shares upon Technion settlement							$ 6
Issuance of shares upon Technion settlement, shares							569,395
Repurchase of common shares, shares						5,076	(5,076)
Vesting of restricted stock units			$ 2	$ 3
Vesting of restricted shares, shares			33,449	54,122	25,132
Ending balance			$ 404	$ 402	$ 361	$ 351	$ 349	$ 274	$ 404	$ 351
Ending balance, shares			39,977,654	39,914,668	35,945,608	35,124,844	34,860,989	27,527,738	39,977,654	35,124,844
Common stock [Member] | At-The-Market Sales Agreement [Member]
Issuance of stock, shares					35,362
Issuance of shares including finance costs					$ 1
Common stock [Member] | Underwritten Public Offering [Member]
Issuance of shares upon equity financing/public offering, net				$ 38			$ 60
Issuance of stock, shares	3,833,334	5,899,500		3,833,334			5,899,500
Equity financing issuance costs	$ (200)
Additional Paid-in Capital [Member]
Beginning balance			$ 168,848	$ 133,383	129,825	$ 120,607	$ 60,782	$ 60,047	$ 129,825	$ 60,047
Exercise of stock options			28	90	25	4	89
Issuance of shares upon exercise/execution of warrants				178			51
Issuance of shares upon Technion settlement							(6)
Vesting of restricted stock units				(3)
Equity financing issuance costs			(50)
Issuance of warrants					421
Stock-based compensation			2,957	3,016	2,658	2,695	6,178	735
Ending balance			171,783	168,848	133,383	123,306	120,607	60,782	171,783	123,306
Additional Paid-in Capital [Member] | At-The-Market Sales Agreement [Member]
Issuance of shares including finance costs					454
Additional Paid-in Capital [Member] | Underwritten Public Offering [Member]
Issuance of shares upon equity financing/public offering, net				32,184			53,513
Accumulated Other Comprehensive Income [Member]
Beginning balance			24	1
Change in unrealized gain (loss) on investments			(12)	23	1
Ending balance			12	24	1				12
Accumulated deficit [Member]
Beginning balance			(112,511)	(98,062)	(86,145)	(60,957)	(47,551)	(38,960)	(86,145)	(38,960)
Net loss			(12,875)	(14,449)	(11,917)	(11,161)	(13,406)	(8,591)
Ending balance			(125,386)	(112,511)	(98,062)	(72,118)	(60,957)	$ (47,551)	(125,386)	(72,118)
Treasury stock [Member]
Beginning balance			$ (1,539)	$ (1,250)	$ (1,129)	$ (83)			$ (1,129)
Beginning balance, shares			(128,697)	(101,890)	(91,423)	(8,385)			(91,423)
Issuance of shares upon exercise/execution of warrants				$ (178)			$ (52)
Issuance of shares upon exercise/execution of warrants, shares				(14,893)			(3,385)
Repurchase of common shares							$ (31)
Repurchase of common shares, shares							(5,000)
Vesting of restricted stock units			$ (46)	$ (111)	$ (121)
Vesting of restricted shares, shares			(10,835)	(11,914)	(10,467)
Ending balance			$ (1,585)	$ (1,539)	$ (1,250)	$ (83)	$ (83)		$ (1,585)	$ (83)
Ending balance, shares			(139,532)	(128,697)	(101,890)	(8,385)	(8,385)		(139,532)	(8,385)

Stockholder's Equity - Schedu_2

Stockholder's Equity - Schedule of Transaction Related to Warrants to Purchase Common Stock (Detail) - $ / shares	3 Months Ended	6 Months Ended	9 Months Ended	12 Months Ended
	Sep. 30, 2019	Jun. 30, 2019	Sep. 30, 2019	Dec. 31, 2018
Stockholders Equity [Abstract]
Warrants outstanding and exercisable beginning balance, Shares		347,241	347,241
Warrants granted, Shares	0		40,834
Warrants exercised, Shares	0	(59,707)	(59,707)
Warrants forfeited, Shares	0		(4,474)
Warrants outstanding and exercisable ending balance, Shares	323,894		323,894	347,241
Warrants outstanding and exercisable beginning balance, Weighted average exercise price		$ 3.77	$ 3.77
Warrants granted, Weighted average exercise price			11.02
Warrants exercised, Weighted average exercise price		$ 3.01	3.01
Warrants forfeited, Weighted average exercise price			40
Warrants outstanding and exercisable ending balance, Weighted average exercise price	$ 4.32		$ 4.32	$ 3.77
Warrants outstanding and exercisable Weighted average remaining contractual life			3 years 11 months 26 days	3 years 11 months 1 day
Warrants granted, Weighted average remaining contractual life			10 years

Stock-based Compensation - Addi

Stock-based Compensation - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended	3 Months Ended		9 Months Ended
	Dec. 31, 2017	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Apr. 20, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options to purchase common stock granted				1,780,200
Exercise price per share				$ 9.43
Expense recognized associated with awards		$ 2,957	$ 2,695	$ 8,631	$ 9,608
Performance Option Awards [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expense recognized associated with awards		$ 24	$ 24	$ 73	$ 73
Chief Executive Officer [Member] | Performance Option Awards [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options to purchase common stock granted	22,427
Restricted stock unit	22,427
Exercise price per share	$ 8
Chief Executive Officer [Member] | Time Vesting Awards [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options to purchase common stock granted	640,785
Restricted stock unit	640,785
Exercise price per share	$ 8
Option vesting description				Subject to continued service through the vesting date, 1/3 of the Time-Vesting Awards will vest and become immediately exercisable on the first anniversary of the grant date, with an additional 1/12 of the Time-Vesting Awards vesting on each quarterly anniversary of the grant date
Chief Executive Officer [Member] | Time Vesting Awards [Member] | First Anniversary of Effective Date [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting rights, percentage	0.33%
Chief Executive Officer [Member] | Time Vesting Awards [Member] | Each Quarterly Anniversary of Effective Date [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting rights, quarterly percentage	0.083%
2018 Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock reserved for issuance						5,000,000
Contractual life of stock options granted				10 years
2018 Plan [Member] | Minimum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Exercisable period of vested options				1 month
2018 Plan [Member] | Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Exercisable period of vested options				3 months

Stock-based Compensation - Tran

Stock-based Compensation - Transactions Related to Grant of Stock Options to Employees and Directors (Detail)	9 Months Ended	12 Months Ended
	Sep. 30, 2019USD ($)$ / sharesshares	Dec. 31, 2018USD ($)$ / sharesshares
Amount
Options outstanding at December 31, 2018 | shares	3,261,719
Granted | shares	1,780,200
Exercised | shares	(91,327)
Forfeited | shares	(153,552)
Options outstanding at September 30, 2019 | shares	4,797,040	3,261,719
Options exercisable at September 30, 2019 | shares	1,730,606
Weighted average exercise price
Options outstanding at December 31, 2018 | $ / shares	$ 13.09
Granted | $ / shares	9.43
Exercised | $ / shares	12.98
Forfeited | $ / shares	12.76
Options outstanding at September 30, 2019 | $ / shares	11.96	$ 13.09
Options exercisable at September 30, 2019 | $ / shares	$ 13.69
Weighted average remaining contractual life
Options outstanding	8 years 6 months 14 days	8 years 6 months 21 days
Options exercisable	7 years 6 months 18 days
Aggregate intrinsic value
Options outstanding | $	$ 1,121,950	$ 11,650,373
Options exercisable | $	$ 1,024,195

Stock-based Compensation - Tr_2

Stock-based Compensation - Transactions Related to Grant of Restricted Stock Units to Employees and Directors (Detail) - Restricted Stock Units [Member]	9 Months Ended
	Sep. 30, 2019$ / sharesshares
Amount
Unvested at December 31, 2018 | shares	554,147
Granted | shares	100,000
Vested | shares	(145,919)
Unvested at September 30, 2019 | shares	508,228
Weighted average grant date fair value price
Unvested at December 31, 2018 | $ / shares	$ 9.34
Granted | $ / shares	11.53
Vested | $ / shares	9.90
Unvested at September 30, 2019 | $ / shares	$ 9.61

Stock-based Compensation - Summ

Stock-based Compensation - Summary of Allocated Stock-based Compensation Expense (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Share-based compensation	$ 2,957	$ 2,695	$ 8,631	$ 9,608
Research and Development Expense [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Share-based compensation	718	498	1,987	909
General and Administrative Expense [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Share-based compensation	$ 2,239	$ 2,197	$ 6,644	$ 8,699

Other Expense (Income), Net - S

Other Expense (Income), Net - Schedule of Other Expense (Income), Net (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Other Income And Expenses [Abstract]
Interest and other income	$ (272)	$ (223)	$ (766)	$ (368)
Investment income, net	(92)		(224)
Interest and other expense	460	24	1,164	75
Total other expense (income), net	$ 96	$ (199)	$ 174	$ (293)

Net Loss Per Share - Weighted A

Net Loss Per Share - Weighted Average Number of Shares Used in Computing Basic and Diluted Net Loss Per Share (Detail) - USD ($) $ / shares in Units, $ in Thousands		3 Months Ended						9 Months Ended
		Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Sep. 30, 2019	Sep. 30, 2018
Numerator:
Net loss		$ (12,875)	$ (14,449)	$ (11,917)	$ (11,161)	$ (13,406)	$ (8,591)	$ (39,241)	$ (33,158)
Denominator:
Shares used in computing net loss per share of common stock, basic and diluted	[1]	39,944,324			35,005,979			37,394,310	31,485,067
Net loss per share of common stock, basic and diluted		$ (0.32)			$ (0.32)			$ (1.05)	$ (1.05)
[1]	The following potentially dilutive securities have been excluded from the computation of diluted weighted average shares outstanding as their effect would be anti-dilutive: Nine months ended September 30, 2019 2018 Options to purchase common stock 4,797,040 3,611,400 Restricted stock units 508,228 767,743 Warrants 323,894 347,241 Total potential common stock equivalents 5,629,162 4,726,384

Net Loss Per Share - Weighted_2

Net Loss Per Share - Weighted Average Number of Shares Used in Computing Basic and Diluted Net Loss Per Share (Parenthetical) (Detail) - shares	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Total potential common stock equivalents	5,629,162	4,726,384
Options to Purchase Common Stock [Member]
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Total potential common stock equivalents	4,797,040	3,611,400
Restricted Stock Units [Member]
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Total potential common stock equivalents	508,228	767,743
Warrants [Member]
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Total potential common stock equivalents	323,894	347,241

Reverse Merger - Additional Inf

Reverse Merger - Additional Information (Detail)	Dec. 19, 2017$ / sharesshares	Sep. 30, 2019$ / shares	Dec. 31, 2018$ / shares
Business Acquisition [Line Items]
Common stock, par value		$ 0.01	$ 0.01
Eloxx Limited [Member]
Business Acquisition [Line Items]
Issuance of shares in exchange of all outstanding capital stock | shares	20,316,656
Common stock, par value	$ 0.01
Reverse stock split	0.05

Reverse Merger - Summary of Est

Reverse Merger - Summary of Estimated Fair Value of Assets Acquired and Liabilities Assumed (Detail) - Eloxx Limited [Member] $ in Thousands	Dec. 19, 2017USD ($)
Business Acquisition [Line Items]
Cash and cash equivalents	$ 123
Prepaid expenses and other current assets	220
Property, plant and equipment, net	39
Restricted bank deposits	6
Total assets acquired	388
Accounts payable	(215)
Accrued expenses	(343)
Total liabilities acquired	(558)
Total net liabilities acquired	$ (170)