Solid Biosciences (SLDB) 10-Q 6 Aug 20 2020 Q2 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	6 Months Ended
	Jun. 30, 2020	Aug. 01, 2020
Cover [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Jun. 30, 2020
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	Q2
Trading Symbol	SLDB
Entity Registrant Name	Solid Biosciences Inc.
Entity Current Reporting Status	Yes
Entity Central Index Key	0001707502
Current Fiscal Year End Date	--12-31
Entity Filer Category	Accelerated Filer
Entity Shell Company	false
Entity Small Business	true
Entity Emerging Growth Company	true
Entity Ex Transition Period	true
Entity Common Stock, Shares Outstanding		46,101,794
Entity File Number	001-38360
Entity Tax Identification Number	90-0943402
Entity Address, Address Line One	141 Portland Street, Fifth Floor
Entity Address, City or Town	Cambridge
Entity Address, State or Province	MA
Entity Address, Postal Zip Code	02139
City Area Code	617
Local Phone Number	337-4680
Entity Interactive Data Current	Yes
Title of 12(b) Security	Common Stock $0.001 par value per share
Security Exchange Name	NASDAQ
Entity Incorporation, State or Country Code	DE
Document Quarterly Report	true
Document Transition Report	false

Condensed Consolidated Balance

Condensed Consolidated Balance Sheets - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Current assets:
Cash and cash equivalents	$ 40,441	$ 76,043
Available-for-sale-securities		7,481
Prepaid expenses and other current assets	3,094	2,778
Total current assets	43,535	86,302
Property and equipment, net	9,582	11,645
Operating lease, right-of-use assets	4,310	4,988
Other non-current assets	209	209
Restricted cash	327	327
Total assets	57,963	103,471
Current liabilities:
Accounts payable	2,793	7,124
Accrued expenses	8,315	9,178
Operating lease liabilities	1,863	1,736
Finance lease liabilities	197	186
Other current liabilities		52
Total current liabilities	13,168	18,276
Operating lease liabilities, excluding current portion	3,450	4,414
Finance lease liabilities, excluding current portion	632	733
Total liabilities	17,250	23,423
Commitments and contingencies (Note 11)
Preferred stock, $0.001 par value; 10,000,000 shares authorized at June 30, 2020 and December 31, 2019; no shares issued and outstanding at June 30, 2020 and December 31, 2019
Common stock, $0.001 par value; 300,000,000 shares authorized at June 30, 2020 and December 31, 2019; 46,068,393 shares issued and outstanding at June 30, 2020 and 45,987,571 shares issued and outstanding at December 31, 2019; 2,295,699 pre-funded warrants outstanding at June 30, 2020 and December 31, 2019	48	48
Additional paid-in capital	402,625	396,278
Accumulated other comprehensive income		1
Accumulated deficit	(361,960)	(316,279)
Total stockholders’ equity	40,713	80,048
Total liabilities and stockholders’ equity	$ 57,963	$ 103,471

Condensed Consolidated Balanc_2

Condensed Consolidated Balance Sheets (Parenthetical) - $ / shares	Jun. 30, 2020	Dec. 31, 2019
Statement Of Financial Position [Abstract]
Preferred stock, par value	$ 0.001	$ 0.001
Preferred stock, shares authorized	10,000,000	10,000,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Common stock, par value	$ 0.001	$ 0.001
Common stock, shares authorized	300,000,000	300,000,000
Common stock, shares issued	46,068,393	45,987,571
Common stock, shares outstanding	45,987,571	45,987,571
Pre-funded warrants outstanding	2,295,699	2,295,699

Condensed Consolidated Statemen

Condensed Consolidated Statements of Operations - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Income Statement [Abstract]
Revenue	$ 0	$ 0	$ 0	$ 0
Operating expenses:
Research and development	13,448	21,610	33,113	44,879
General and administrative	5,526	5,359	10,776	12,392
Restructuring charges			1,944
Total operating expenses	18,974	26,969	45,833	57,271
Loss from operations	(18,974)	(26,969)	(45,833)	(57,271)
Other income (expense):
Interest (expense) income	(13)	367	151	875
Other income		77	1	289
Total other income (expense), net	(13)	444	152	1,164
Net loss	$ (18,987)	$ (26,525)	$ (45,681)	$ (56,107)
Net loss per share attributable to common stockholders, basic and diluted	$ (0.39)	$ (0.76)	$ (0.95)	$ (1.61)
Weighted average shares of common stock outstanding, basic and diluted	48,163,094	34,843,344	48,111,186	34,810,101

Condensed Consolidated Statem_2

Condensed Consolidated Statements of Comprehensive Loss - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Statement Of Income And Comprehensive Income [Abstract]
Net loss	$ (18,987)	$ (26,525)	$ (45,681)	$ (56,107)
Other comprehensive loss:
Unrealized (loss) gain on available-for-sale securities	1	(4)	(1)	8
Comprehensive loss	$ (18,986)	$ (26,529)	$ (45,682)	$ (56,099)

Condensed Consolidated Statem_3

Condensed Consolidated Statements of Changes in Stockholders' Equity - USD ($) $ in Thousands	Total	Common Stock [Member]	Additional Paid In Capital [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Accumulated Deficit [Member]
Beginning balance at Dec. 31, 2018	$ 125,183	$ 35	$ 324,209	$ (5)	$ (199,056)
Beginning balance, units at Dec. 31, 2018		35,432,460
Equity-based compensation	7,411		7,411
Net loss	(56,107)				(56,107)
Forfeiture of restricted stock awards units		(33,566)
Unrealized gain (loss) on available for sale securities	8			8
Ending balance at Jun. 30, 2019	76,495	$ 35	331,620	3	(255,163)
Ending balance, units at Jun. 30, 2019		35,398,894
Beginning balance at Mar. 31, 2019	99,113	$ 35	327,709	7	(228,638)
Beginning balance, units at Mar. 31, 2019		35,414,914
Equity-based compensation	3,911		3,911
Net loss	(26,525)				(26,525)
Forfeiture of restricted stock awards units		(16,020)
Unrealized gain (loss) on available for sale securities	(4)			(4)
Ending balance at Jun. 30, 2019	76,495	$ 35	331,620	3	(255,163)
Ending balance, units at Jun. 30, 2019		35,398,894
Beginning balance at Dec. 31, 2019	80,048	$ 48	396,278	1	(316,279)
Beginning balance, units at Dec. 31, 2019		48,283,270
Equity-based compensation	6,347		6,347
Net loss	(45,681)				(45,681)
Vesting of restricted stock, units		121,975
Forfeiture of restricted stock awards units		(41,153)
Unrealized gain (loss) on available for sale securities	(1)			(1)
Ending balance at Jun. 30, 2020	40,713	$ 48	402,625		(361,960)
Ending balance, units at Jun. 30, 2020		48,364,092
Beginning balance at Mar. 31, 2020	56,456	$ 48	399,382	(1)	(342,973)
Beginning balance, units at Mar. 31, 2020		48,366,423
Equity-based compensation	3,243		3,243
Net loss	(18,987)				(18,987)
Forfeiture of restricted stock awards units		(2,331)
Unrealized gain (loss) on available for sale securities	1			$ 1
Ending balance at Jun. 30, 2020	$ 40,713	$ 48	$ 402,625		$ (361,960)
Ending balance, units at Jun. 30, 2020		48,364,092

Condensed Consolidated Statem_4

Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019
Cash flows from operating activities:
Net loss	$ (45,681)	$ (56,107)
Adjustments to reconcile net loss to net cash used in operating activities:
Amortization of (discount)/premium on available-for-sale securities	(20)	(235)
Equity-based compensation expense	6,347	7,411
Depreciation expense	2,360	1,254
Changes in operating assets and liabilities:
Prepaid expenses and other current and non-current assets	362	(4,301)
Accounts payable	(3,892)	2,437
Accrued expenses and other current and non-current liabilities	(1,818)	(2,687)
Net cash used in operating activities	(42,342)	(52,228)
Cash flows from investing activities:
Purchases of property and equipment	(759)	(3,092)
Proceeds from sale and maturities of available-for-sale securities	7,900	43,349
Purchases of available-for-sale securities	(401)	(22,559)
Net cash provided by investing activities	6,740	17,698
Cash flows from financing activities:
Net decrease in cash, cash equivalents and restricted cash	(35,602)	(34,530)
Cash, cash equivalents, and restricted cash at beginning of period	76,370	86,693
Cash, cash equivalents, and restricted cash at end of period	40,768	52,163
Supplemental disclosure of non-cash investing and financing activities:
Operating lease liabilities arising from obtaining right-of-use asset		1,629
Property and equipment included in accounts payable and accruals	$ 27	$ 395

Nature of the Business and Basi

Nature of the Business and Basis of Presentation	6 Months Ended
	Jun. 30, 2020
Accounting Policies [Abstract]
Nature of the Business and Basis of Presentation	1. Nature of the Business and Basis of Presentation Nature of Business Solid Biosciences Inc. was organized in March 2013 under the name SOLID Ventures Management, LLC. In October 2013, the company changed its name to Solid Ventures, LLC and in June 2015, the company changed its name to Solid Biosciences, LLC. The company operated as a Delaware limited liability company under the name Solid Biosciences, LLC until immediately prior to the effectiveness of its registration statement on Form S-1 on January 25, 2018, at which time it completed a statutory corporate conversion into a Delaware corporation (the “Corporate Conversion”) and changed its name to Solid Biosciences Inc. (the “Company”). In addition, entities formed solely for the purpose of holding membership interests in the Company’s limited liability company were merged with and into the Company. As a result of the Corporate Conversion, all of the Series 1 and 2 Senior Preferred, Junior Preferred Units, Series A, B, C and D Common Units of Solid Biosciences, LLC converted into shares of common stock of Solid Biosciences Inc. on a one for 0.8485 basis and all of the unit holders of Solid Biosciences, LLC became holders of common stock of Solid Biosciences Inc. The Company’s mission is to cure Duchenne muscular dystrophy (“Duchenne”), a genetic muscle-wasting disease predominantly affecting boys. It is caused by mutations in the dystrophin gene, which result in the absence or near-absence of dystrophin protein. Dystrophin protein works to strengthen muscle fibers and protect them from daily wear and tear. Without functioning dystrophin and certain associated proteins, muscles suffer excessive damage from normal daily activities and are unable to regenerate, leading to the build-up of fibrotic, or scar, and fat tissue. The Company’s lead product candidate, SGT-001, is a gene transfer candidate under investigation for its ability to drive functional dystrophin protein expression in patients’ muscles and improve the course of the disease. SGT-001 has been granted Rare Pediatric Disease Designation and Fast Track in the United States and Orphan Drug Designations in both the United States and European Union. The Company filed an Investigational New Drug application (“IND”) in September 2017 and initiated a Phase I/II clinical trial for SGT-001 in the United States during the fourth quarter of 2017 , which is called IGNITE DMD. In November 2019, IGNITE DMD was placed on clinical hold by the U.S. Food and Drug Administration (“FDA”). In April 2020, the Company submitted a response to the FDA that included changes to the clinical protocol designed to enhance patient safety, as well as information related to improvements to its manufacturing process. The FDA responded by maintaining the clinical hold and requesting further data and analyses relating to this manufacturing process. In June 2020, the Company submitted a response to the FDA that provided data related to manufacturing process improvements. In July 2020, the Company announced that the FDA responded by maintaining the clinical hold and requesting further manufacturing information and updated safety and efficacy data for all patients dosed in the trial, as well as providing direction on the total viral load to be administered per patient. The Company is evaluating next steps and plans to continue its dialogue with the FDA to determine the appropriate path for SGT-001. The Company is subject to risks and uncertainties common to early-stage companies in the biotechnology industry, including, but not limited to, development by competitors of new technological innovations, dependence on licenses, protection of proprietary technology, dependence on key personnel, compliance with government regulations and the need to obtain additional financing to fund operations. Product candidates currently under development will require significant additional research and development efforts, including extensive pre-clinical studies and clinical trials and regulatory approval, prior to commercialization. These efforts require significant amounts of additional capital, adequate personnel infrastructure and extensive compliance and reporting capabilities. The Company’s product candidates are in development. There can be no assurance that the Company’s research and development will be successfully completed, that adequate protection for the Company’s intellectual property will be obtained, that any products developed will obtain necessary government regulatory approval or that any approved products will be commercially viable. Even if the Company’s product development efforts are successful, it is uncertain when, if ever, the Company will generate significant revenue from product sales. The Company operates in an environment of rapid change in technology and substantial competition from, among others, other pharmaceutical and biotechnology companies. In addition, the Company is dependent upon the services of its employees, partners and consultants. Liquidity The accompanying condensed consolidated financial statements have been prepared on a basis that assumes the Company will continue as a going concern and which contemplates the realization of assets and satisfaction of liabilities and commitments in the ordinary course of business. Through June 30, 2020, the Company has funded its operations primarily with the proceeds from the sale of redeemable preferred units and member units as well as the sale of common stock and prefunded warrants to purchase shares of its common stock in private placements and the sale of common stock in its initial public offering. In accordance with Accounting Standards Codification (“ASC”) 205-40, Going Concern, the Company has evaluated whether there are conditions and events, considered in the aggregate, that raise substantial doubt about the Company’s ability to continue as a going concern within one year after the date the financial statements are issued. As of June 30, 2020, the Company had an accumulated deficit of $361,960. During the three and six months ended June 30, 2020, the Company incurred a net loss of $18,987 and $45,681, respectively, and the Company used $42,342 of cash in operations for the six months ended June 30, 2020. The Company expects to continue to generate operating losses in the foreseeable future. Based upon its current operating plan, the Company expects that its cash and cash equivalents of $40,441 as of June 30, 2020 will be sufficient to fund its operating expenses and capital requirements into the first quarter of 2021. In accordance with the requirements of ASC 205-40, the Company determined that there is substantial doubt about the Company’s ability to continue as a going concern within twelve months of the issuance date of these financial statements. The financial statements do not include any adjustments that might result from the outcome of this uncertainty. Although the Company has been successful in raising capital in the past, there is no assurance that it will be successful in obtaining such additional financing on terms acceptable to the Company, if at all, nor is it considered probable under the accounting standards. As such, under the requirements of ASC 205-40, management may not consider the potential for future capital raises or management plans to reduce costs that are not considered probable in its assessment of the Company’s ability to meet its obligations for the next twelve months. If the Company is unable to obtain funding, the Company would be forced to delay, reduce or eliminate some or all of its research and development programs, pre-clinical and clinical testing or commercialization efforts, which could adversely affect its business prospects. The accompanying condensed consolidated financial statements have been prepared in accordance with accounting principles generally accepted in the United States of America (“GAAP”). The accompanying condensed consolidated financial statements include the accounts of Solid Biosciences Inc. and its wholly owned or controlled subsidiaries. All intercompany accounts and transactions have been eliminated. In the opinion of management, the Company’s accompanying unaudited condensed consolidated financial statements include all adjustments, consisting of normal recurring accruals, necessary for a fair statement of the Company’s financial statements for interim periods in accordance with GAAP. The information included in this quarterly report on Form 10-Q should be read in conjunction with the Company’s consolidated financial statements and the accompanying notes included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2019. The year-end condensed consolidated balance sheet data presented for comparative purposes was derived from the Company’s audited financial statements but does not include all disclosures required by GAAP.

Summary of Significant Accounti

Summary of Significant Accounting Policies	6 Months Ended
	Jun. 30, 2020
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	2. Summary of Significant Accounting Policies The Company’s accounting policies are described in the “Notes to Consolidated Financial Statements” in its Annual Report on Form 10-K for the year ended December 31, 2019 and updated, as necessary, in this report. Use of Estimates The preparation of the Company’s condensed consolidated financial statements in conformity with GAAP requires management to make estimates, judgments and assumptions that affect the reported amounts of assets and liabilities, the disclosure of contingent assets and liabilities at the date of the condensed consolidated financial statements and the reported amounts of expenses during the reporting periods. Significant estimates and assumptions reflected in these condensed consolidated financial statements include, but are not limited to, the recognition of research and development expenses and equity-based compensation. Estimates are periodically reviewed in light of changes in circumstances, facts and experience. Changes in estimates are recorded in the period in which they become known. The full extent to which the COVID-19 pandemic will directly or indirectly impact the Company’s business, results of operations and financial condition, including clinical trials and employee-related amounts, will depend on future developments that are highly uncertain, including new information that may emerge concerning COVID-19 and the actions taken to contain it or treat its impact. The Company has made estimates of the impact of COVID-19 within its financial statements and there may be changes to those estimates in future periods. Actual results could differ from the Company’s estimates. Cash Equivalents The Company considers all short-term, highly liquid investments with original maturities of 90 days or less at acquisition date to be cash equivalents. Restricted Cash The Company held restricted cash of $327 in separate restricted bank accounts as security deposits for leases of the Company’s facilities as of June 30, 2020 and December 31, 2019. The Company has included restricted cash of $327 as a non-current asset as of June 30, 2020 and December 31, 2019. A reconciliation of the amounts of cash and cash equivalents and restricted cash from the cash flow statement to the balance sheet is as follows: June 30, 2020 December 31, 2019 Cash and cash equivalents as presented on balance sheet $ 40,441 $ 76,043 Restricted cash, non-current, as presented on balance sheet 327 327 Cash and cash equivalents and restricted cash as presented on cash flow statement $ 40,768 $ 76,370 Segment Data The Company manages its operations as a single segment for the purposes of assessing performance and making operating decisions. The Company’s singular focus is on developing treatments through gene therapy and other means for patients with Duchenne. All of the Company’s tangible assets are held in the United States. Recently Adopted Accounting Pronouncements In August 2018, the Financial Accounting Standards Board issued ASU No. 2018-13 , Fair Value Measurement (Topic 820): Disclosure Framework - Changes to the Disclosure Requirements for Fair Value Measurement Recently Issued Accounting Pronouncements In June 2016, the Financial Accounting Standards Board (“FASB”) issued ASU No. 2016-13, Financial Instruments—Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments Codification Improvements to Topic 326, Financial Instruments—Credit Losses Financial Instruments—Credit Losses (Topic 326): Targeted Transition Relief This standard will be effective for the Company on January 1, 2023. .

Fair Value of Financial Assets

Fair Value of Financial Assets and Liabilities	6 Months Ended
	Jun. 30, 2020
Fair Value Disclosures [Abstract]
Fair Value of Financial Assets and Liabilities	3. Fair Value of Financial Assets and Liabilities The following tables present information about the Company’s assets and liabilities that are measured at fair value on a recurring basis and indicate the level of the fair value hierarchy utilized to determine such fair values: Fair Value Measurements as of June 30, 2020 Using: Level 1 Level 2 Level 3 Total Assets: Cash equivalents $ — $ 14,462 $ — $ 14,462 $ — $ 14,462 $ — $ 14,462 Fair Value Measurements as of December 31, 2019 Using: Level 1 Level 2 Level 3 Total Assets: Cash equivalents $ — $ 50,037 $ — $ 50,037 Available-for-sale securities — 7,481 — 7,481 $ — $ 57,518 $ — $ 57,518 As of June 30, 2020, there were no available-for-sale securities. As of December 31, 2019, the fair values of the Company’s available-for-sale debt securities were determined using Level 2 inputs. At December 31, 2019, the Company’s portfolio of available-for-sale securities consisted of corporate bond securities and commercial paper. During the six months ended June 30, 2020 and the year ended December 31, 2019, there were no transfers between Level 1, Level 2 and Level 3. The fair value of the Company’s cash, restricted cash, accounts payable, and accrued expenses and other current liabilities approximate their carrying value due to their short-term maturities.

Available-for-Sale Securities

Available-for-Sale Securities	6 Months Ended
	Jun. 30, 2020
Investments Debt And Equity Securities [Abstract]
Available-for-Sale Securities	4. Available-for-Sale Securities As of June 30, 2020, there were no available-for-sale securities. As of December 31, 2019, the fair value of available-for-sale securities by type of security was as follows: December 31, 2019 Amortized Cost Gross Unrealized Gain Gross Unrealized Loss Fair Value Investments: Corporate bond securities 1,502 1 — 1,503 Commercial paper 5,978 — — 5,978 $ 7,480 $ 1 $ — $ 7,481 The estimated fair value and amortized cost of the Company’s available-for-sale securities by contractual maturity are summarized as follows: December 31, 2019 Amortized Cost Fair Value Due in one year or less $ 7,480 $ 7,481 Total available-for-sale securities $ 7,480 $ 7,481 The weighted average maturity of the Company’s available-for-sale securities as of

Property and Equipment

Property and Equipment	6 Months Ended
	Jun. 30, 2020
Property Plant And Equipment [Abstract]
Property and Equipment	5. Property and Equipment Property and equipment consists of the following: June 30, 2020 December 31, 2019 Furniture and fixtures $ 203 $ 203 Laboratory equipment 9,616 9,425 Leasehold improvements 4,686 4,686 Computer equipment 436 428 Computer software 541 372 Construction in process 1,251 1,322 16,733 16,436 Less accumulated depreciation 7,151 4,791 $ 9,582 $ 11,645 Depreciation expense was $1,334 and $2,360 for the three and six months ended June 30, 2020, respectively, and $658 and $1,254 for the three and six months ended June 30, 2019, respectively.

Prepaid Expenses and Other Curr

Prepaid Expenses and Other Current Assets	6 Months Ended
	Jun. 30, 2020
Deferred Costs Capitalized Prepaid And Other Assets Disclosure [Abstract]
Prepaid Expenses and Other Current Assets	6. Prepaid Expenses and Other Current Assets Prepaid expenses and other current assets consist of the following: June 30, 2020 December 31, 2019 Prepaid research and development expenses $ 642 $ 1,290 Prepaid expenses and other assets 2,452 1,488 $ 3,094 $ 2,778

Accrued Expenses and Other Curr

Accrued Expenses and Other Current Liabilities	6 Months Ended
	Jun. 30, 2020
Payables And Accruals [Abstract]
Accrued Expenses and Other Current Liabilities	7. Accrued Expenses and Other Current Liabilities Accrued expenses and other current liabilities consist of the following: June 30, 2020 December 31, 2019 Accrued research and development $ 3,898 $ 3,742 Accrued compensation 3,257 3,583 Accrued other 1,160 1,853 $ 8,315 $ 9,178

Stockholders' Equity

Stockholders' Equity	6 Months Ended
	Jun. 30, 2020
Equity [Abstract]
Stockholders' Equity	8. Stockholders’ Equity On July 30, 2019, the Company issued and sold in a private placement (i) 10,607,525 shares of its common stock at a price per share of $4.65 and (ii) 2,295,699 pre-funded warrants to purchase shares of its common stock at a price per warrant of $4.64. Each pre-funded warrant is exercisable for one share of common stock at an exercise price of $0.01 and the pre-funded warrants have no expiration date. The Company received gross proceeds from the private placement of $59,977, before deducting offering costs of $2,079. No warrants were exercised during the three or six months ended June 30, 2020 and no warrants were outstanding during the three or six months ended June 30, 2019.

Equity-Based Compensation

Equity-Based Compensation	6 Months Ended
	Jun. 30, 2020
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Equity-Based Compensation	9. Equity-Based Compensation In connection with the closing of the Company’s initial public offering, the board of directors and stockholders approved the 2018 Omnibus Incentive Plan, which provides for the reservation of 5,001,000 shares of common stock for equity awards. On June 16, 2020, the Company’s stockholders approved the 2020 Equity Incentive Plan (“2020 Plan”) which consists of (i) 3,000,000 shares of common stock and (ii) additional shares of common stock (up to 4,879,025)as is equal to (i) the number of shares reserved under the Company’s 2018 Omnibus Incentive Plan (“2018 Plan”) that remain available for grant under the 2018 Plan as of immediately prior to the date the 2020 Plan was approved by the Company’s stockholders and (ii) the number of shares subject to awards granted under the 2018 Plan which awards expire, terminate or are otherwise surrendered, cancelled, forfeited or repurchased by the Company at their original issuance price pursuant to a contractual repurchase right. During the three and six months ended June 30, 2020, the Company granted options for the purchase of 581,800 and 1,397,916 shares of common stock, respectively. During the three and six months ended , the Company granted 436,065 and 1,393,720 restricted stock units, respectively. The Company recorded equity-based compensation expense related to all of its share-based awards to employees and non-employees in the following captions within its condensed consolidated statements of operations: Three Months Ended June 30, Six Months Ended June 30, 2020 2019 2020 2019 Research and development $ 1,616 $ 2,114 $ 2,855 $ 3,933 General and administrative 1,627 1,797 2,641 3,478 Restructuring — — 851 — Total $ 3,243 $ 3,911 $ 6,347 $ 7,411

Income Taxes

Income Taxes	6 Months Ended
	Jun. 30, 2020
Income Tax Disclosure [Abstract]
Income Taxes	10. Income Taxes During the three and six months ended June 30, 2020 and 2019, the Company recorded no income tax benefits for the net operating losses incurred or for the research and development tax credits and orphan drug credits generated in each year due to its uncertainty of realizing a benefit from those items. The Company has provided a valuation allowance for the full amount of its net deferred tax assets because, at June 30, 2020 As of June 30, 2020, and December 31, 2019, the Company had not recorded any amounts for unrecognized tax benefits. The Company files income tax returns as prescribed by the tax laws of the jurisdictions in which it operates. In the normal course of business, the Company is subject to examination by federal and state jurisdictions, where applicable. There are currently no pending income tax examinations. The Company’s C-Corporation tax years beginning with the year ended December 31, 2018 are open under statute. Any tax credit or net operating loss carryforward can be adjusted in future periods after the respective year of generation’s statute of limitation has closed.

Commitments and Contingencies

Commitments and Contingencies	6 Months Ended
	Jun. 30, 2020
Commitments And Contingencies Disclosure [Abstract]
Commitments and Contingencies	11. Commitments and Contingencies Legal Proceedings The Company may periodically become subject to legal proceedings and claims arising in connection with ongoing business activities, including claims or disputes related to patents that have been issued or that are pending in the field of research on which the Company is focused. The Company is not aware of any material claims as of June 30, 2020.

Net Loss per Share

Net Loss per Share	6 Months Ended
	Jun. 30, 2020
Earnings Per Share [Abstract]
Net Loss per Share	12. Net Loss per Share Basic and diluted net loss per share attributable to common stockholders were calculated as follows: The numerator for basic and diluted net loss per share attributable to common stockholders is as follows: Three Months Ended June 30, Six Months Ended June 30, 2020 2019 2020 2019 Net loss attributable to common stockholders $ (18,987 ) $ (26,525 ) $ (45,681 ) $ (56,107 ) The denominator is as follows: Three Months Ended June 30, Six Months Ended June 30, 2020 2019 2020 2019 Weighted average shares of common stock outstanding, basic and diluted 48,163,094 34,843,344 48,111,186 34,810,101 Net loss per share attributable to common stockholders, basic and diluted is as follows: Three Months Ended June 30, Six Months Ended June 30, 2020 2019 2020 2019 Net loss per share attributable to common stockholders $ (0.39 ) $ (0.76 ) $ (0.95 ) $ (1.61 ) The following potential common stock equivalents, presented based on amounts outstanding at each period end, were excluded from the calculation of diluted net loss per share attributable to common stockholders for the periods indicated because including them would have had an anti-dilutive effect for the three and six months ended June 30 2020 2019 Options to purchase shares of common stock 3,607,953 2,730,362 Unvested shares of common stock 184,171 523,687 Unvested restricted stock units 1,421,095 — 5,213,219 3,254,049

Restructuring

Restructuring	6 Months Ended
	Jun. 30, 2020
Restructuring And Related Activities [Abstract]
Restructuring	13. Restructuring In January 2020, the Company’s board of directors approved a restructuring plan to reduce operating costs and better align the Company’s workforce with the needs of its business following the Company’s November 2019 announcement that the SGT-001 IGNITE DMD trial was placed on clinical hold by the U.S. Food and Drug Administration. Under the restructuring plan, the Company made changes to its management team and reduced headcount by approximately 30 percent. Affected employees were eligible to receive severance payments and outplacement services in connection with the restructuring plan. During the three and six months ended June 30, 2020, the Company recorded aggregate restructuring charges of $0 and $1,944, respectively, related to severance payments and other employee-related costs. The Company does not expect to incur any additional significant costs associated with this restructuring. During the three and six months ended June 30, 2020, $462 and $1,425, respectively, of the estimated restructuring charges were paid. The Company expects the remaining accrued restructuring costs of $519 will be paid in the next nine months. The following table shows the total amount expected to be incurred and the liability related to the 2020 restructuring for the three and six months ended June 30, 2020: One-Time Employee Termination Benefits Accrued restructuring costs as of December 31, 2019 $ - Restructuring charges incurred during the period 1,944 Amounts paid during the period (963 ) Accrued restructuring costs as of March 31, 2020 $ 981 Amounts paid during the period (462 ) Accrued restructuring costs as of June 30, 2020 $ 519

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	6 Months Ended
	Jun. 30, 2020
Accounting Policies [Abstract]
Use of Estimates	Use of Estimates The preparation of the Company’s condensed consolidated financial statements in conformity with GAAP requires management to make estimates, judgments and assumptions that affect the reported amounts of assets and liabilities, the disclosure of contingent assets and liabilities at the date of the condensed consolidated financial statements and the reported amounts of expenses during the reporting periods. Significant estimates and assumptions reflected in these condensed consolidated financial statements include, but are not limited to, the recognition of research and development expenses and equity-based compensation. Estimates are periodically reviewed in light of changes in circumstances, facts and experience. Changes in estimates are recorded in the period in which they become known. The full extent to which the COVID-19 pandemic will directly or indirectly impact the Company’s business, results of operations and financial condition, including clinical trials and employee-related amounts, will depend on future developments that are highly uncertain, including new information that may emerge concerning COVID-19 and the actions taken to contain it or treat its impact. The Company has made estimates of the impact of COVID-19 within its financial statements and there may be changes to those estimates in future periods. Actual results could differ from the Company’s estimates.
Cash Equivalents	Cash Equivalents The Company considers all short-term, highly liquid investments with original maturities of 90 days or less at acquisition date to be cash equivalents.
Restricted Cash	Restricted Cash The Company held restricted cash of $327 in separate restricted bank accounts as security deposits for leases of the Company’s facilities as of June 30, 2020 and December 31, 2019. The Company has included restricted cash of $327 as a non-current asset as of June 30, 2020 and December 31, 2019. A reconciliation of the amounts of cash and cash equivalents and restricted cash from the cash flow statement to the balance sheet is as follows: June 30, 2020 December 31, 2019 Cash and cash equivalents as presented on balance sheet $ 40,441 $ 76,043 Restricted cash, non-current, as presented on balance sheet 327 327 Cash and cash equivalents and restricted cash as presented on cash flow statement $ 40,768 $ 76,370
Segment Data	Segment Data The Company manages its operations as a single segment for the purposes of assessing performance and making operating decisions. The Company’s singular focus is on developing treatments through gene therapy and other means for patients with Duchenne. All of the Company’s tangible assets are held in the United States.
Recently Adopted Accounting Pronouncements	Recently Adopted Accounting Pronouncements In August 2018, the Financial Accounting Standards Board issued ASU No. 2018-13 , Fair Value Measurement (Topic 820): Disclosure Framework - Changes to the Disclosure Requirements for Fair Value Measurement
Recently Issued Accounting Pronouncements	Recently Issued Accounting Pronouncements In June 2016, the Financial Accounting Standards Board (“FASB”) issued ASU No. 2016-13, Financial Instruments—Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments Codification Improvements to Topic 326, Financial Instruments—Credit Losses Financial Instruments—Credit Losses (Topic 326): Targeted Transition Relief This standard will be effective for the Company on January 1, 2023. .

Summary of Significant Accoun_3

Summary of Significant Accounting Policies (Tables)	6 Months Ended
	Jun. 30, 2020
Accounting Policies [Abstract]
Reconciliation of Amounts From Cash Flow Statement to Balance Sheet	A reconciliation of the amounts of cash and cash equivalents and restricted cash from the cash flow statement to the balance sheet is as follows: June 30, 2020 December 31, 2019 Cash and cash equivalents as presented on balance sheet $ 40,441 $ 76,043 Restricted cash, non-current, as presented on balance sheet 327 327 Cash and cash equivalents and restricted cash as presented on cash flow statement $ 40,768 $ 76,370

Fair Value of Financial Asset_2

Fair Value of Financial Assets and Liabilities (Tables)	6 Months Ended
	Jun. 30, 2020
Fair Value Disclosures [Abstract]
Summary of Assets and Liabilities Measured at Fair Value on Recurring Basis and Indicate Level of Fair Value Hierarchy Utilized	The following tables present information about the Company’s assets and liabilities that are measured at fair value on a recurring basis and indicate the level of the fair value hierarchy utilized to determine such fair values: Fair Value Measurements as of June 30, 2020 Using: Level 1 Level 2 Level 3 Total Assets: Cash equivalents $ — $ 14,462 $ — $ 14,462 $ — $ 14,462 $ — $ 14,462 Fair Value Measurements as of December 31, 2019 Using: Level 1 Level 2 Level 3 Total Assets: Cash equivalents $ — $ 50,037 $ — $ 50,037 Available-for-sale securities — 7,481 — 7,481 $ — $ 57,518 $ — $ 57,518

Available-for-Sale Securities (

Available-for-Sale Securities (Tables)	6 Months Ended
	Jun. 30, 2020
Investments Debt And Equity Securities [Abstract]
Schedule of Fair Value of Available-for-Sale Securities by Type of Security	As of June 30, 2020, there were no available-for-sale securities. As of December 31, 2019, the fair value of available-for-sale securities by type of security was as follows: December 31, 2019 Amortized Cost Gross Unrealized Gain Gross Unrealized Loss Fair Value Investments: Corporate bond securities 1,502 1 — 1,503 Commercial paper 5,978 — — 5,978 $ 7,480 $ 1 $ — $ 7,481
Summary Estimated Fair Value and Amortized Cost of Available-for-Sale Securities by Contractual Maturity	The estimated fair value and amortized cost of the Company’s available-for-sale securities by contractual maturity are summarized as follows: December 31, 2019 Amortized Cost Fair Value Due in one year or less $ 7,480 $ 7,481 Total available-for-sale securities $ 7,480 $ 7,481

Property and Equipment (Tables)

Property and Equipment (Tables)	6 Months Ended
	Jun. 30, 2020
Property Plant And Equipment [Abstract]
Summary of Property and Equipment	Property and equipment consists of the following: June 30, 2020 December 31, 2019 Furniture and fixtures $ 203 $ 203 Laboratory equipment 9,616 9,425 Leasehold improvements 4,686 4,686 Computer equipment 436 428 Computer software 541 372 Construction in process 1,251 1,322 16,733 16,436 Less accumulated depreciation 7,151 4,791 $ 9,582 $ 11,645

Prepaid Expenses and Other Cu_2

Prepaid Expenses and Other Current Assets (Tables)	6 Months Ended
	Jun. 30, 2020
Deferred Costs Capitalized Prepaid And Other Assets Disclosure [Abstract]
Schedule of Prepaid Expenses and Other Current Assets	Prepaid expenses and other current assets consist of the following: June 30, 2020 December 31, 2019 Prepaid research and development expenses $ 642 $ 1,290 Prepaid expenses and other assets 2,452 1,488 $ 3,094 $ 2,778

Accrued Expenses and Other Cu_2

Accrued Expenses and Other Current Liabilities (Tables)	6 Months Ended
	Jun. 30, 2020
Payables And Accruals [Abstract]
Summary of Accrued Expenses and Other Current Liabilities	Accrued expenses and other current liabilities consist of the following: June 30, 2020 December 31, 2019 Accrued research and development $ 3,898 $ 3,742 Accrued compensation 3,257 3,583 Accrued other 1,160 1,853 $ 8,315 $ 9,178

Equity-Based Compensation (Tabl

Equity-Based Compensation (Tables)	6 Months Ended
	Jun. 30, 2020
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Schedule of Equity-based Compensation Expense	The Company recorded equity-based compensation expense related to all of its share-based awards to employees and non-employees in the following captions within its condensed consolidated statements of operations: Three Months Ended June 30, Six Months Ended June 30, 2020 2019 2020 2019 Research and development $ 1,616 $ 2,114 $ 2,855 $ 3,933 General and administrative 1,627 1,797 2,641 3,478 Restructuring — — 851 — Total $ 3,243 $ 3,911 $ 6,347 $ 7,411

Net Loss per Share (Tables)

Net Loss per Share (Tables)	6 Months Ended
	Jun. 30, 2020
Earnings Per Share [Abstract]
Schedule of Basic and Diluted Net Loss per Share Attributable to Common Stockholders	The numerator for basic and diluted net loss per share attributable to common stockholders is as follows: Three Months Ended June 30, Six Months Ended June 30, 2020 2019 2020 2019 Net loss attributable to common stockholders $ (18,987 ) $ (26,525 ) $ (45,681 ) $ (56,107 ) The denominator is as follows: Three Months Ended June 30, Six Months Ended June 30, 2020 2019 2020 2019 Weighted average shares of common stock outstanding, basic and diluted 48,163,094 34,843,344 48,111,186 34,810,101 Net loss per share attributable to common stockholders, basic and diluted is as follows: Three Months Ended June 30, Six Months Ended June 30, 2020 2019 2020 2019 Net loss per share attributable to common stockholders $ (0.39 ) $ (0.76 ) $ (0.95 ) $ (1.61 )
Schedule of Antidilutive Securities Excluded from Calculation of Diluted Net Loss per Share Attributable to Common Stockholders	The following potential common stock equivalents, presented based on amounts outstanding at each period end, were excluded from the calculation of diluted net loss per share attributable to common stockholders for the periods indicated because including them would have had an anti-dilutive effect for the three and six months ended June 30 2020 2019 Options to purchase shares of common stock 3,607,953 2,730,362 Unvested shares of common stock 184,171 523,687 Unvested restricted stock units 1,421,095 — 5,213,219 3,254,049

Restructuring (Tables)

Restructuring (Tables)	6 Months Ended
	Jun. 30, 2020
Restructuring And Related Activities [Abstract]
Schedule of Total Amount Expected to be Incurred and Liability Related to Restructuring	The following table shows the total amount expected to be incurred and the liability related to the 2020 restructuring for the three and six months ended June 30, 2020: One-Time Employee Termination Benefits Accrued restructuring costs as of December 31, 2019 $ - Restructuring charges incurred during the period 1,944 Amounts paid during the period (963 ) Accrued restructuring costs as of March 31, 2020 $ 981 Amounts paid during the period (462 ) Accrued restructuring costs as of June 30, 2020 $ 519

Nature of the Business and Ba_2

Nature of the Business and Basis of Presentation - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019	Jan. 25, 2018
Nature Of Business And Basis Of Presentation [Line Items]
Net loss	$ 18,987	$ 26,525	$ 45,681	$ 56,107
Accumulated deficit	361,960		361,960		$ 316,279
Net cash used in operating activities			42,342	$ 52,228
Cash and cash equivalents	$ 40,441		$ 40,441		$ 76,043
Corporate Conversion [Member]
Nature Of Business And Basis Of Presentation [Line Items]
Common stock, conversion ratio						84.85%

Summary of Significant Accoun_4

Summary of Significant Accounting Policies - Additional Information (Detail) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Accounting Policies [Abstract]
Restricted cash deposit	$ 327	$ 327
Restricted cash noncurrent	$ 327	$ 327

Summary of Significant Accoun_5

Summary of Significant Accounting Policies - Reconciliation of Amounts From Cash Flow Statement to Balance Sheet (Detail) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019	Jun. 30, 2019	Dec. 31, 2018
Reconciliation Of Beginning And End Of Period Amounts From Cash Flow Statement To Balance Sheet [Abstract]
Cash and cash equivalents as presented on balance sheet	$ 40,441	$ 76,043
Restricted cash, non-current, as presented on balance sheet	327	327
Cash and cash equivalents and restricted cash as presented on cash flow statement	$ 40,768	$ 76,370	$ 52,163	$ 86,693

Fair Value of Financial Asset_3

Fair Value of Financial Assets and Liabilities - Summary of Assets and Liabilities Measured at Fair Value on Recurring Basis and Indicate Level of Fair Value Hierarchy Utilized (Detail) - USD ($)	Jun. 30, 2020	Dec. 31, 2019
Assets:
Cash equivalents	$ 14,462,000	$ 50,037,000
Available-for-sale securities	0	7,481,000
Assets Fair Value Disclosure	14,462,000	57,518,000
Level 2 [Member]
Assets:
Cash equivalents	14,462,000	50,037,000
Available-for-sale securities		7,481,000
Assets Fair Value Disclosure	$ 14,462,000	$ 57,518,000

Fair Value of Financial Asset_4

Fair Value of Financial Assets and Liabilities - Additional Information (Detail) - USD ($)	6 Months Ended	12 Months Ended
	Jun. 30, 2020	Dec. 31, 2019
Fair Value Disclosures [Abstract]
Available-for-sale securities	$ 0	$ 7,481,000
Fair value, assets, level 1 to level 2 transfers, amount	0	0
Fair value, assets, level 2 to level 1 transfers, amount	0	0
Fair value, assets, transfers into level 3, amount	0	0
Fair value, assets, transfers out of level 3, amount	$ 0	$ 0

Available-for-Sale Securities -

Available-for-Sale Securities - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2019	Jun. 30, 2020
Investments Debt And Equity Securities [Abstract]
Available-for-sale securities	$ 7,481,000	$ 0
Available-for-sale securities weighted average maturity period	2 months 12 days

Available-for-Sale Securities_2

Available-for-Sale Securities - Schedule of Fair Value of Available-for-Sale Securities by Type of Security (Detail) - USD ($)	Jun. 30, 2020	Dec. 31, 2019
Debt Securities, Available-for-sale [Line Items]
Amortized Cost		$ 7,480,000
Gross Unrealized Gain		1,000
Fair Value	$ 0	7,481,000
Corporate Bond Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Amortized Cost		1,502,000
Gross Unrealized Gain		1,000
Fair Value		1,503,000
Commercial Paper [Member]
Debt Securities, Available-for-sale [Line Items]
Amortized Cost		5,978,000
Fair Value		$ 5,978,000

Available-for-Sale Securities_3

Available-for-Sale Securities - Summary Estimated Fair Value and Amortized Cost of Available-for-Sale Securities by Contractual Maturity (Detail) - USD ($)	Jun. 30, 2020	Dec. 31, 2019
Investments Debt And Equity Securities [Abstract]
Due in one year or less, amortized cost		$ 7,480,000
Amortized Cost		7,480,000
Due in one year or less, fair value		7,481,000
Total available-for-sale securities, fair value	$ 0	$ 7,481,000

Property and Equipment - Summar

Property and Equipment - Summary of Property and Equipment (Detail) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 16,733	$ 16,436
Less accumulated depreciation	7,151	4,791
Property and equipment, net	9,582	11,645
Furniture and Fixtures [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	203	203
Laboratory Equipment [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	9,616	9,425
Leasehold Improvements [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	4,686	4,686
Computer Equipment [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	436	428
Computer Software [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	541	372
Construction in Progress [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 1,251	$ 1,322

Property and Equipment - Additi

Property and Equipment - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Property Plant And Equipment [Abstract]
Depreciation expense	$ 1,334	$ 658	$ 2,360	$ 1,254

Prepaid Expenses and Other Cu_3

Prepaid Expenses and Other Current Assets - Schedule of Prepaid Expenses and Other Current Assets (Detail) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Deferred Costs Capitalized Prepaid And Other Assets Disclosure [Abstract]
Prepaid research and development expenses	$ 642	$ 1,290
Prepaid expenses and other assets	2,452	1,488
Prepaid expenses and other current assets	$ 3,094	$ 2,778

Accrued Expenses and Other Cu_3

Accrued Expenses and Other Current Liabilities - Summary of Accrued Expenses and Other Current Liabilities (Detail) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Accrued Expenses And Other Current Liabilities [Line Items]
Accrued expenses and other current liabilities	$ 8,315	$ 9,178
Accrued Research and Development [Member]
Accrued Expenses And Other Current Liabilities [Line Items]
Accrued expenses and other current liabilities	3,898	3,742
Accrued Compensation [Member]
Accrued Expenses And Other Current Liabilities [Line Items]
Accrued expenses and other current liabilities	3,257	3,583
Accrued Other [Member]
Accrued Expenses And Other Current Liabilities [Line Items]
Accrued expenses and other current liabilities	$ 1,160	$ 1,853

Stockholders' Equity - Addition

Stockholders' Equity - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands	Jul. 30, 2019	Jun. 30, 2020	Jun. 30, 2020	Dec. 31, 2019	Jun. 30, 2019
Class Of Stock [Line Items]
Gross proceeds from private placement	$ 59,977
Warrants outstanding		2,295,699	2,295,699	2,295,699	0
Private Placement [Member]
Class Of Stock [Line Items]
Offering costs	$ 2,079
Common Stock [Member] | Private Placement [Member]
Class Of Stock [Line Items]
Stock issued and sold	10,607,525
Stock price per share	$ 4.65
Pre-Funded Warrants [Member]
Class Of Stock [Line Items]
Warrants exercised		0	0
Pre-Funded Warrants [Member] | Private Placement [Member]
Class Of Stock [Line Items]
Warrants to purchase common stock	2,295,699
Warrants price per share	$ 4.64
Warrants exercisable for common stock	1
Exercise price of warrant	$ 0.01

Equity-Based Compensation - Add

Equity-Based Compensation - Additional Information (Detail) - shares	Jun. 16, 2020	Jun. 30, 2020	Jun. 30, 2020
2018 Omnibus Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares authorized for common stock for equity awards		5,001,000	5,001,000
Common stock purchased		581,800	1,397,916
2018 Omnibus Incentive Plan [Member] | Restricted Stock Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted stock units granted		436,065	1,393,720
2020 Equity Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares authorized for common stock for equity awards	3,000,000
2020 Equity Incentive Plan [Member] | Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of additional shares authorized for common stock for equity awards	4,879,025

Equity-Based Compensation - Sch

Equity-Based Compensation - Schedule of Equity-based Compensation Expense (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	$ 3,243	$ 3,911	$ 6,347	$ 7,411
Research and Development [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	1,616	2,114	2,855	3,933
General and Administrative [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	$ 1,627	$ 1,797	2,641	$ 3,478
Restructuring [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense			$ 851

Income Taxes - Additional Infor

Income Taxes - Additional Information (Detail) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019
Income Tax Disclosure [Abstract]
Income tax expense (benefit)	$ 0	$ 0	$ 0	$ 0
Unrecognized tax benefits	$ 0		$ 0		$ 0

Net Loss per Share - Schedule o

Net Loss per Share - Schedule of Basic and Diluted Net Loss per Share Attributable to Common Stockholders (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Earnings Per Share Basic [Line Items]
Net loss attributable to common stockholders	$ (18,987)	$ (26,525)	$ (45,681)	$ (56,107)
Weighted average shares of common stock outstanding, basic and diluted	48,163,094	34,843,344	48,111,186	34,810,101
Net loss per share attributable to common stockholders	$ (0.39)	$ (0.76)	$ (0.95)	$ (1.61)
Common Stock [Member]
Earnings Per Share Basic [Line Items]
Weighted average shares of common stock outstanding, basic and diluted	48,163,094	34,843,344	48,111,186	34,810,101

Net Loss per Share - Schedule_2

Net Loss per Share - Schedule of Antidilutive Securities Excluded from Calculation of Diluted Net Loss per Share Attributable to Common Stockholders (Detail) - shares	6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Common stock equivalents excluded from calculation of diluted net loss per share	5,213,219	3,254,049
Options to Purchase Shares of Common Stock [Member]
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Common stock equivalents excluded from calculation of diluted net loss per share	3,607,953	2,730,362
Unvested Restricted Stock Units [Member]
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Common stock equivalents excluded from calculation of diluted net loss per share	1,421,095
Unvested Shares of Common Stock [Member]
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Common stock equivalents excluded from calculation of diluted net loss per share	184,171	523,687

Restructuring- Additional Infor

Restructuring- Additional Information (Detail) $ in Thousands	3 Months Ended	6 Months Ended
	Jun. 30, 2020USD ($)	Jun. 30, 2020USD ($)
Restructuring Costs [Abstract]
Number of headcount reduced, percentage		30.00%
Restructuring charges related to severance payment and other employee-related costs	$ 0	$ 1,944
Restructuring charges were paid	462	1,425
Restructuring costs	$ 519	$ 519

Restructuring - Schedule of Tot

Restructuring - Schedule of Total Amount Expected to be Incurred and Liability Related to Restructuring (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2020
Restructuring Costs [Line Items]
Restructuring charges incurred during the period			$ 1,944
Amounts paid during the period	$ (462)		(1,425)
Accrued restructuring costs as of March 31, 2020	519		519
One-Time Employee Termination Benefits [Member]
Restructuring Costs [Line Items]
Accrued restructuring costs as of December 31, 2019	981
Restructuring charges incurred during the period		$ 1,944
Amounts paid during the period	(462)	(963)
Accrued restructuring costs as of March 31, 2020	$ 519	$ 981	$ 519