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Document and Entity Information - shares	3 Months Ended
Document and Entity Information - shares	Mar. 31, 2018	May 01, 2018
Document And Entity Information [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Mar. 31, 2018
Document Fiscal Year Focus	2018
Document Fiscal Period Focus	Q1
Trading Symbol	sldb
Entity Registrant Name	Solid Biosciences Inc.
Entity Central Index Key	0001707502
Current Fiscal Year End Date	--12-31
Entity Filer Category	Non-accelerated Filer
Entity Common Stock, Shares Outstanding		35,461,959

Condensed Consolidated Balance Sheets - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Current assets:
Cash and cash equivalents	$ 164,773	$ 52,080
Available-for-sale-securities	17,609	17,014
Prepaid expenses and other current assets	1,931	1,499
Restricted cash	65	65
Total current assets	184,378	70,658
Property and equipment, net	4,418	2,429
Other non-current assets	209
Restricted cash	237
Deferred offering costs		3,106
Total assets	189,242	76,193
Current liabilities:
Accounts payable	5,835	5,066
Accrued expenses and other current liabilities	4,092	6,205
Total current liabilities	9,927	11,271
Other non-current liabilities	365
Total liabilities	10,292	11,271
Commitments and contingencies (Note 10)
Stockholders' / Members' equity / (deficit):
Series A, B, C and D Common Units, no units authorized at March 31, 2018 and 20,189,509 units authorized at December 31, 2017; no units issued and outstanding at March 31, 2018 and 19,438,552 units issued and outstanding at December 31, 2017		65,014
Preferred stock, $0.001 par value; 10,000,000 shares authorized at March 31, 2018 and no shares authorized at December 31,2017; no shares issued and outstanding at March 31, 2018 and December 31, 2017
Common stock, $0.001 par value; 300,000,000 shares authorized at March 31, 2018 and no shares authorized at December 31, 2017; 35,476,892 shares issued and outstanding at March 31, 2018 and no shares issued and outstanding at December 31, 2017	35
Additional paid-in capital	319,073
Accumulated other comprehensive loss	(23)	(13)
Accumulated deficit	(140,135)	(124,258)
Total stockholders'/members' equity/(deficit)	178,950	(59,257)
Total liabilities, preferred units and stockholders'/members' equity	$ 189,242	76,193
Series 2 Senior Preferred Units [Member]
Preferred Units
Preferred Units		55,002
Series 1 Senior Preferred Units [Member]
Preferred Units
Preferred Units		25,000
Junior Preferred Units [Member]
Preferred Units
Preferred Units		$ 44,177

Condensed Consolidated Balance Sheets (Parenthetical) - $ / shares	Mar. 31, 2018	Dec. 31, 2017
Series A, B, C and D common units, authorized	0	20,189,509
Series A, B, C and D common units, issued	0	19,438,552
Series A, B, C and D common units, outstanding	0	19,438,552
Preferred stock, par value	$ 0.001	$ 0.001
Preferred stock, shares authorized	10,000,000	0
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	0
Common stock, shares issued	35,476,892	0
Common stock, shares outstanding	35,476,892	0
Series 2 Senior Preferred Units [Member]
Preferred units, authorized	0	4,886,000
Preferred units, issued	0	4,886,000
Preferred units, outstanding	0	4,886,000
Series 1 Senior Preferred Units [Member]
Preferred units, authorized	0	2,500,000
Preferred units, issued	0	2,500,000
Preferred units, outstanding	0	2,500,000
Junior Preferred Units [Member]
Preferred units, authorized	0	4,414,356
Preferred units, issued	0	4,414,356
Preferred units, outstanding	0	4,414,356

Condensed Consolidated Statements of Operations - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Income Statement [Abstract]
Revenue	$ 0	$ 0
Operating expenses:
Research and development	11,929	8,733
General and administrative	4,044	5,380
Total operating expenses	15,973	14,113
Loss from operations	(15,973)	(14,113)
Other income (expense):
Interest income	65	62
Other income	31	176
Total other income (expense), net	96	238
Net loss	(15,877)	(13,875)
Net loss attributable to non-controlling interest		(1,060)
Net loss attributable to Solid Biosciences Inc.	(15,877)	(12,815)
Accretion of preferred units to redemption value		(959)
Redemption of preferred units		15,685
Redemption of redeemable interest from non-controlling interest in Solid GT		(1,925)
Net loss attributable to common stockholders	$ (15,877)	$ (14)
Net loss per share attributable to common stockholders, basic and diluted	$ (0.54)	$ (0.01)
Weighted average shares of common stock outstanding, basic and diluted	29,354,650	3,047,759

Condensed Consolidated Statements of Comprehensive Loss - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Statement of Comprehensive Income [Abstract]
Net loss	$ (15,877)	$ (13,875)
Other comprehensive loss:
Unrealized loss on available-for-sale securities	(10)	(23)
Comprehensive loss	(15,887)	(13,898)
Comprehensive loss attributable to non-controlling interest		(1,060)
Comprehensive loss attributable to Solid Biosciences Inc.	$ (15,887)	$ (12,838)

Condensed Consolidated Statements of Preferred Units and Stockholders' /Members' Equity/(Deficit) - USD ($) $ in Thousands	Total	Series A, B, C and D Common Units [Member]	Series 1 Senior Preferred Units [Member]	Redeemable Preferred Units [Member]	Series 2 Senior Preferred Units [Member]	Junior Preferred Units [Member]	Common Stock [Member]	Additional Paid In Capital [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Accumulated Members' Deficit [Member]	Accumulated Members' Deficit [Member] Series 1 Senior Preferred Units [Member]	Accumulated Members' Deficit [Member] Redeemable Preferred Units [Member]	Total Members' Deficit [Member]	Total Members' Deficit [Member] Series 1 Senior Preferred Units [Member]	Total Members' Deficit [Member] Redeemable Preferred Units [Member]	Noncontrolling Interest [Member]	Series B Common Units in exchange for Series A Common Units [Member] Series A, B, C and D Common Units [Member]	Series D Common Units in Exchange for Series A Common Units [Member] Series A, B, C and D Common Units [Member]	Series A Common Units in Exchange for Redeemable Preferred Units [Member]	Series A Common Units in Exchange for Redeemable Preferred Units [Member] Series A, B, C and D Common Units [Member]	Series A Common Units in Exchange for Redeemable Preferred Units [Member] Total Members' Deficit [Member]	Series D Common Units [Member]	Series D Common Units [Member] Series A, B, C and D Common Units [Member]	Series D Common Units [Member] Accumulated Members' Deficit [Member]	Series D Common Units [Member] Total Members' Deficit [Member]	Series D Common Units [Member] Noncontrolling Interest [Member]	Series C Common Units in Exchange for Class B Non-controlling Interest in Solid GT [Member] Series A, B, C and D Common Units [Member]	Series C Common Units in Exchange for Class B Non-controlling Interest in Solid GT [Member] Total Members' Deficit [Member]	Series C Common Units in Exchange for Class B Non-controlling Interest in Solid GT [Member] Noncontrolling Interest [Member]	Series D Common Units in Exchange for Class C Non-controlling Interest in Solid GT [Member] Series A, B, C and D Common Units [Member]	Series D Common Units in Exchange for Class C Non-controlling Interest in Solid GT [Member] Total Members' Deficit [Member]	Series D Common Units in Exchange for Class C Non-controlling Interest in Solid GT [Member] Noncontrolling Interest [Member]
Ending balance, units at Dec. 31, 2017			2,500,000		4,886,000	4,414,356
Ending balance, units at Dec. 31, 2017	19,438,552	19,438,552
Beginning balance at Dec. 31, 2016				$ 71,649
Redeemable Preferred Units
Conversion of units into shares of common stock, units																				12,219,299							1,635,916			1,083,205
Beginning balance, units at Dec. 31, 2016				17,100,000
Redeemable Preferred Units
Conversion of units into shares of common stock, value																			$ 55,964	$ 55,964	$ 55,964						$ 2,053	$ 2,053	$ (2,053)	$ 1,409	$ 1,409	$ (1,409)
Issuance of preferred units, value			$ 24,041		$ 55,002	$ 44,177
Issuance of preferred units, units			2,500,000		4,886,000	4,414,356
Accretion (decretion) in redemption value of preferred units			$ 959
Redemption of preferred units				$ (15,685)
Issuance of Series A common units in exchange for redeemable preferred units, units				(17,100,000)
Issuance of Series A common units in exchange for redeemable preferred units, value				$ (55,964)
Ending balance at Dec. 31, 2017			$ 25,000		$ 55,002	$ 44,177
Ending balance, units at Dec. 31, 2017			2,500,000		4,886,000	4,414,356
Members' Deficit
Conversion of units into shares of common stock, value																			$ 55,964	$ 55,964	$ 55,964						$ 2,053	$ 2,053	$ (2,053)	$ 1,409	$ 1,409	$ (1,409)
Conversion of units into shares of common stock, units																				12,219,299							1,635,916			1,083,205
Issuance of common stock upon initial public offering, net of offering cost, units																							838,689
Equity-based compensation	$ 5,330	$ 5,030											$ 5,030			$ 300
Net loss	(53,178)									$ (52,118)			(52,118)			(1,060)
Unrealized loss on available for sale securities	(36)								$ (36)				(36)
Ending balance at Dec. 31, 2017	(59,257)	65,014							(13)	(124,258)			(59,257)
Beginning balance at Dec. 31, 2016	$ (37,886)	$ 558							23	(84,941)			(84,360)			$ 46,474
Beginning balance, units at Dec. 31, 2016		5,123,917,000
Members' Deficit
Accretion (decretion) in redemption value of preferred units			$ (959)								$ (959)			$ (959)
Redemption of preferred units				$ 15,685								$ 15,685			$ 15,685
Issuance of common units in exchange for common units																	(1,301,520)	(160,954)
Issuance of junior preferred units in redemption of Class D non-controlling interest in Solid GT																						$ (44,177)		$ (1,925)	$ (1,925)	$ (42,252)
Ending balance, units at Dec. 31, 2017	19,438,552	19,438,552
Ending balance, units at Mar. 31, 2018			0		0	0
Ending balance, units at Mar. 31, 2018	0						35,476,892
Redeemable Preferred Units
Conversion of units into shares of common stock, units		(19,429,620)	(2,500,000)	0	(4,886,000)	(4,414,356)	26,498,559
Beginning balance, units at Dec. 31, 2017			2,500,000		4,886,000	4,414,356
Redeemable Preferred Units
Conversion of units into shares of common stock, value	$ 124,179	$ (65,180)	$ (25,000)		$ (55,002)	$ (44,177)	$ 26	$ 189,333					124,179
Ending balance, units at Mar. 31, 2018			0		0	0
Members' Deficit
Conversion of units into shares of common stock, value	124,179	$ (65,180)	$ (25,000)		$ (55,002)	$ (44,177)	$ 26	189,333					124,179
Conversion of units into shares of common stock, units		(19,429,620)	(2,500,000)	0	(4,886,000)	(4,414,356)	26,498,559
Issuance of common stock upon initial public issuance, net of issuance costs of $4,592	129,096						$ 9	129,087					129,096
Issuance of common stock upon initial public offering, net of offering cost, units							8,984,375
Equity-based compensation	819	$ 166						653					819
Net loss	(15,877)									(15,877)			(15,877)
Repurchase of common units/ shares of common stock		(8,932)					(6,042)
Unrealized loss on available for sale securities	(10)								(10)				(10)
Ending balance at Mar. 31, 2018	178,950						$ 35	$ 319,073	(23)	(140,135)			178,950
Beginning balance at Dec. 31, 2017	$ (59,257)	$ 65,014							$ (13)	$ (124,258)			$ (59,257)
Beginning balance, units at Dec. 31, 2017	19,438,552	19,438,552
Ending balance, units at Mar. 31, 2018	0						35,476,892

Condensed Consolidated Statements of Preferred Units and Stockholders' /Members' Equity/(Deficit) (Parenthetical) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2018	Dec. 31, 2017
Net issuance costs, issuance of common stock upon initial public offering	$ 4,592
Common Stock [Member]
Net issuance costs, issuance of common stock upon initial public offering	4,592
Additional Paid In Capital [Member]
Net issuance costs, issuance of common stock upon initial public offering	4,592
Total Members' Deficit [Member]
Net issuance costs, issuance of common stock upon initial public offering	$ 4,592
Series 1 Senior Preferred Units [Member]
Issuance costs		$ 500
Tranche right		$ 459

Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Cash flows from operating activities:
Net loss	$ (15,877)	$ (13,875)
Adjustments to reconcile net loss to net cash used in operating activities:
Amortization of premium on available-for-sale securities	5	107
Equity-based compensation expense	819	3,230
Depreciation expense	227	51
Changes in operating assets and liabilities:
Prepaid expenses and other current and non-current assets	(641)	184
Accounts payable	(354)	832
Accrued expenses and other current and non-current liabilities	(1,351)	(725)
Net cash used in operating activities	(17,172)	(10,196)
Cash flows from investing activities:
Purchases of property and equipment	(1,001)	(248)
Proceeds from sale and maturities of available-for-sale securities	8,509	7,210
Purchases of available-for-sale securities	(9,119)
Net cash (used in) provided by investing activities	(1,611)	6,962
Cash flows from financing activities:
Proceeds from issuance of Series 1 Senior Preferred units		25,000
Proceeds from initial public offering of common stock, net of commissions and underwriting discounts	133,688
Payment of deferred offering costs	(1,975)	(178)
Net cash provided by financing activities	131,713	24,822
Net increase in cash, cash equivalents and restricted cash	112,930	21,588
Cash, cash equivalents and restricted cash at beginning of period	52,145	7,843
Cash, cash equivalents, and restricted cash at end of period	165,075	29,431
Supplemental disclosure of non-cash investing and financing activities:
Accretion to redemption value for redeemable preferred units		(959)
Redemption of preferred units		15,685
Redemption of redeemable interest from non-controlling interest in Solid GT		(1,925)
Deferred offering costs included in accounts payable	193	54
Offering costs included in accounts payable		500
Property and equipment included in accounts payable	1,479	16
Series A, B, C and D Common Units [Member]
Supplemental disclosure of non-cash investing and financing activities:
Conversion of units into shares of common stock	65,180
Series D Common Units in Exchange for Series A Common Units [Member]
Supplemental disclosure of non-cash investing and financing activities:
Issuance of units		638
Series A Common Units in Exchange for Redeemable Preferred Units [Member]
Supplemental disclosure of non-cash investing and financing activities:
Issuance of units		55,964
Series C Common Units in Exchange for Class B Non-controlling Interest in Solid GT [Member]
Supplemental disclosure of non-cash investing and financing activities:
Issuance of units		2,053
Series D Common Units in Exchange for Class C Non-controlling Interest in Solid GT [Member]
Supplemental disclosure of non-cash investing and financing activities:
Issuance of units		1,409
Series 2 Senior Preferred Units [Member]
Supplemental disclosure of non-cash investing and financing activities:
Conversion of units into shares of common stock	55,002
Series 1 Senior Preferred Units [Member]
Supplemental disclosure of non-cash investing and financing activities:
Conversion of units into shares of common stock	25,000
Junior Preferred Units [Member]
Supplemental disclosure of non-cash investing and financing activities:
Conversion of units into shares of common stock	$ 44,177
Junior Preferred Units Upon Redemption of Class D Non-controlling Interest in Solid GT [Member]
Supplemental disclosure of non-cash investing and financing activities:
Issuance of units		$ 44,177

Nature of the Business and Basis of Presentation	3 Months Ended
Nature of the Business and Basis of Presentation	Mar. 31, 2018
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”). As a result of the Corporate Conversion, all of the Series 1 and 2 Senior Preferred Units, 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 (“DMD”), 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 under development to restore functional dystrophin protein expression in patients’ muscles. SGT-001 has been granted Rare Pediatric Disease Designation in the United States and Orphan Drug Designations in both the United States and European Union. The Company filed an Investigational New Drug application, or 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. In November 2017, the FDA notified the Company that the Company was not permitted to dose patients in the higher-dose group of IGNITE DMD due to a partial clinical hold. The partial clinical hold related to the number of vials and manufacturing lots utilized per patient, as well as manufacturing processes to support the higher-dose group. The Company has since submitted a response to the FDA and was notified that the partial clinical hold has been resolved. In March 2018, the Company announced that IGNITE DMD was placed on full clinical hold following an unexpected serious adverse event reported in the first patient dosed in the clinical trial. The Company has since received a formal clinical hold letter in which the FDA has requested additional information, including an assessment of the etiology of the event, the patient’s clinical status and laboratory parameters, and any additional measures to address patient safety. The Company is finalizing its response to the FDA letter. 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. *Initial Public Offering in January 2018* On January 30, 2018, the Company completed its initial public offering with the sale of 8,984,375 shares of common stock, including shares of common stock issued upon the exercise in full of the underwriters’ over-allotment option, at a public offering price of $16.00 per share, resulting in net proceeds of $129,096, after deducting underwriting discounts and commissions and offering expenses. *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 March 31, 2018, the Company has funded its operations primarily with the proceeds from the private placements of preferred units and member units and its recently completed initial public offering. The Company has incurred recurring losses from operations since its inception, including a net loss of $15,877 and $13,875 for the three months ended March 31, 2018 and 2017, respectively. In addition, as of March 31, 2018, the Company had an accumulated deficit of $140,135. The Company expects to continue to generate operating losses for the foreseeable future. As of March 31, 2018, the Company had cash, cash equivalents and available-for-sale securities of $182,382. The Company believes that its cash, cash equivalents and available-for-sale securities as of March 31, 2018 will enable it to fund its operating expenses and capital expenditure requirements through at least the next 12 months from the issuance of these financial statements. To execute its business plans, the Company will need substantial funding to support its continuing operations and pursue its growth strategy. Until the Company can generate significant revenue from product sales, if ever, it expects to finance its operations through the sale of public or private equity, debt financings or other capital sources, potentially including collaborations with other companies or other strategic transactions. The Company may not be able to obtain financing on acceptable terms, or at all. Even if the Company is able to secure financing, the terms of any financing may adversely affect the holdings or the rights of the Company’s stockholders. If the Company is unable to obtain funding, the Company could 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. Although management continues to pursue these plans, there is no assurance that the Company will be successful in obtaining sufficient financing on terms acceptable to the Company to fund continuing operations, if at all. *Merger and Recapitalization in March 2017* The Company had historically owned 100% of the voting units of its wholly owned subsidiary, Solid GT, LLC (“Solid GT”), and the results of Solid GT are included in the Company’s condensed consolidated financial statements. In November 2015, Solid GT issued voting units to new investors which decreased the Company’s voting ownership in Solid GT to 77%. The Company continued to consolidate the results of Solid GT into its financial statements as the Company owned a majority voting interest in Solid GT and directed the activities of Solid GT. However, because the Company controlled but owned less than 100% of Solid GT, the Company recorded a non-controlling ownership interest at its fair value at inception and recognizes the net loss or profit attributable to non-controlling interests in the condensed consolidated statements of operations based on a profit and loss sharing arrangement between the Company and the non-controlling interests. The Company also presents the change in equity related to equity-based compensation issued to Solid GT employees by Solid GT in non-controlling interest. On March 29, 2017, the Company merged the operations of Solid GT into the Company and Solid GT ceased to exist as a legal entity. The proportionate share of the loss attributed to the non-controlling interest amounted to $1,060 for the three months ended March 31, 2017. There was no loss attributed to the non-controlling interest for the three months ended March 31, 2018 since the merger was completed on March 29, 2017. See Note 3, Merger and Recapitalization, for additional information. 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 the Company 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 (condensed consolidated financial statements) include all adjustments, consisting of normal recurring accruals, necessary for a fair presentation 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, 2017. The results of operations for the three months ended March 31, 2018 are not necessarily indicative of the operating results for the full year or for any other subsequent interim period.

Summary of Significant Accounting Policies

3 Months Ended

Mar. 31, 2018

Accounting Policies [Abstract]

Summary of Significant Accounting Policies

2. Summary of Significant Accounting Policies

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. 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 $302 in separate restricted bank accounts as security deposits for the lease of the Company’s facilities as of March 31, 2018. The Company has included restricted cash of $65 as a current asset and restricted cash of $237 as a non-current asset as of March 31, 2018.

The Company held restricted cash of $65 in a separate restricted bank account as a security deposit for the lease of the Company’s facility as of December 31, 2017. The Company has included the restricted cash of $65 as a current asset as of December 31, 2017.

Available-for-Sale Securities

Available-for-sale securities consist of investments with original maturities greater than 90 days at acquisition date. The Company has classified its investments with maturities beyond one year as short term, based on their highly liquid nature and because such available-for-sale securities represent the investment of cash that is available for current operations.

The Company classifies all of its investments as available-for-sale securities. The Company’s investments are measured and reported at fair value using quoted prices in active markets for similar securities. Unrealized gains and losses on available-for-sale debt securities are reported as a separate component of stockholders’ equity. The cost of securities sold is determined on a specific identification basis, and realized gains and losses are included in other income (expense) within the condensed consolidated statement of operations. If any adjustment to fair value reflects a decline in the value of the investment that the Company considers to be “other than temporary,” the Company reduces the investment to fair value through a charge to the condensed consolidated statement of operations. No such adjustments were necessary during the periods presented.

Concentration of Credit Risk and of Significant Suppliers

Financial instruments that potentially expose the Company to concentrations of credit risk consist primarily of cash and cash equivalents. Periodically, the Company maintains deposits in accredited financial institutions in excess of federally insured limits. The Company maintains each of its cash balances with high-quality and accredited financial institutions and accordingly, such funds are not exposed to significant credit risk. The Company does not believe that it is subject to unusual credit risk beyond the normal credit risk associated with commercial banking relationships.

The Company is dependent on third-party manufacturers to supply products for research and development activities of its programs, including clinical and pre-clinical testing. These programs could be adversely affected by a significant interruption in the supply of such drug substance products.

Fair Value Measurements

Certain assets and liabilities are carried at fair value under GAAP. Fair value is defined as the exchange price that would be received for an asset or paid to transfer a liability (an exit price) in the principal or most advantageous market for the asset or liability in an orderly transaction between market participants on the measurement date. Valuation techniques used to measure fair value must maximize the use of observable inputs and minimize the use of unobservable inputs. Financial assets and liabilities carried at fair value are to be classified and disclosed in one of the following three levels of the fair value hierarchy, of which the first two are considered observable and the last is considered unobservable:

•

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

•

Level 2—Observable inputs (other than Level 1 quoted prices), such as quoted prices in active markets for similar assets or liabilities, quoted prices in markets that are not active for identical or similar assets or liabilities or other inputs that are observable or can be corroborated by observable market data.

•

Level 3—Unobservable inputs that are supported by little or no market activity and that are significant to determining the fair value of the assets or liabilities, including pricing models, discounted cash flow methodologies and similar techniques.

The Company’s cash equivalents and available-for-sale securities are carried at fair value, determined according to the fair value hierarchy described above. See Note 4, Fair Value of Financial Assets and Liabilities, for additional information. The carrying values of the Company’s accounts payable and accrued expenses and other current liabilities approximate their fair value due to the short-term nature of these liabilities.

Equity-Based Compensation

In connection with the completion of the Company’s initial public offering, the Company adopted the 2018 Omnibus Incentive Plan, which provides for the issuance of share-based awards, including options to purchase common stock. The 2018 Omnibus Incentive Plan provides for the awarding of up to 5,001,000 shares of common stock for equity awards.

The Company measures all stock options and other stock-based awards granted to employees and directors based on the fair value on the date of the grant and recognizes compensation expense of those awards, over the requisite service period, which is generally the vesting period of the respective award. Forfeitures are accounted for as they occur. The Company applies the straight-line method of expense recognition to all awards with only service-based vesting conditions. The Company has not issued any awards with performance-based vesting conditions.

For stock-based awards granted to non-employees, compensation expense is recognized over the period during which services are rendered by such non-employees until completed. At the end of each financial reporting period prior to the completion of the service, the fair value of these awards is remeasured using the then-current fair value of the Company’s common stock and updated assumption inputs in the Black-Scholes option-pricing model.

The fair value of each stock option grant is estimated on the date of grant using the Black-Scholes option-pricing model. The Company historically has been a private company and lacks company-specific historical and implied volatility information. Therefore, it estimates its expected stock volatility based on the historical volatility of a publicly traded set of peer companies and expects to continue to do so until such time as it has adequate historical data regarding the volatility of its own traded stock price. For options with service-based vesting conditions, the expected term of the Company’s stock options has been determined utilizing the “simplified” method for awards that qualify as “plain-vanilla” options. The expected term of stock options granted to non-employees is equal to the contractual term of the option award. The risk-free interest rate is determined by reference to the U.S. Treasury yield curve in effect at the time of grant of the award for time periods approximately equal to the expected term of the award. Expected dividend yield is based on the fact that the Company has never paid cash dividends and does not expect to pay any cash dividends in the foreseeable future.

Through January 25, 2018, the Company granted restricted common units to employees, directors and non-employees. In connection with the Company’s Corporate Conversion on January 25, 2018, all restricted common units were converted to restricted shares of common stock.

The Company measures restricted common stock granted to employees and directors based on the fair value on the date of grant and recognizes compensation expense of those awards over the requisite service period, which is generally the vesting period of the respective award. Forfeitures are accounted for as they occur. The Company generally issued restricted common stock with only service-based vesting conditions and records the expense for these awards using the straight-line method. The Company has not issued any awards with performance-based vesting conditions.

The Company measured restricted common stock awards granted to consultants and non-employees based on the fair value of the award on the date of grant. Compensation expense is recognized over the period during which services are rendered by such consultants and non-employees until completed. At the end of each financial reporting period prior to completion of the service, the fair value of unvested awards is remeasured using the then-current fair value of the Company’s common stock.

The Company classifies stock-based compensation expense in its condensed consolidated statement of operations and comprehensive loss in the same manner in which the award recipient’s payroll costs are classified or in which the award recipient’s service payments are classified.

Income Taxes

Income taxes are accounted for under the asset and liability method. Under the asset and liability method, deferred tax assets and liabilities are recognized for the future tax consequences attributable to differences between the financial statement carrying amounts of existing assets and liabilities and their respective tax bases. Deferred tax assets and liabilities are measured using enacted tax rates expected to apply to taxable income in the years in which those temporary differences are expected to be recovered or settled. The effect on deferred tax assets and liabilities of a change in tax rates is recognized in income in the period that includes the enactment date. The Company records valuation allowances to reduce deferred income tax assets to the amount that is more likely than not to be realized. The Company determines whether it is more likely than not that a tax position will be sustained upon examination. If it is not more likely than not that a position will be sustained, no amount of benefit attributable to the position is recognized. The tax benefit to be recognized of any tax position that meets the more likely than not recognition threshold is calculated as the largest amount that is more than 50% likely of being realized upon resolution of the contingency.

Prior to the January 25, 2018, the Company had not been subject to U.S. federal income taxes as the Company was organized as a limited liability company. As such, the taxable income or loss was passed through to and included in the tax returns of the members. Since January 25, 2018, the Company’s income has since been subject to U.S. federal, state, local, and foreign income taxes and taxed at the prevailing corporate tax rates.

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 DMD. All of the Company’s tangible assets are held in the United States.

Comprehensive Loss

Comprehensive loss includes net loss, as well as other changes in stockholders’/members’ equity/(deficit) that result from transactions and economic events other than those with stockholders and members. The Company’s only element of other comprehensive income (loss) in all periods presented was unrealized gains (losses) from available-for-sale securities.

Net Loss per Share

The Company follows the two-class method when computing net loss per share, as the Company has issued shares that meet the definition of participating securities. The two-class method determines net loss per share for each class of common and participating securities according to dividends declared or accumulated and participation rights in undistributed earnings. The two-class method requires income available to common stockholders for the period to be allocated between common and participating securities based upon their respective rights to receive dividends as if all income for the period had been distributed.

Basic net loss per share attributable to common stockholders is computed by dividing the net loss attributable to common stockholders by the weighted average number of shares of common stock outstanding for the period. Diluted net loss attributable to common stockholders is computed by adjusting net loss attributable to common stockholders to reallocate undistributed earnings based on the potential impact of dilutive securities. Diluted net loss per share attributable to common stockholders is computed by dividing the diluted net loss attributable to common stockholders by the weighted average number of shares of common stock outstanding for the period, including potential dilutive shares of common stock assuming the dilutive effect of common stock equivalents.

The Company’s preferred stock contractually entitles the holders of such shares to participate in dividends but does not contractually require the holders of such shares to participate in losses of the Company. Accordingly, in periods in which the Company reports a net loss, such losses are not allocated to such participating securities. In periods in which the Company reports a net loss attributable to common stockholders, diluted net loss per share attributable to common stockholders is the same as basic net loss per share attributable to common stockholders, since dilutive shares of common stock are not assumed to have been issued if their effect is anti-dilutive.

Contingencies

Loss contingency provisions are recorded if the potential loss from any claim, asserted or unasserted, or legal proceeding is considered probable and the amount can be reasonably estimated or a range of loss can be determined. These accruals represent the Company’s best estimate of probable loss. Disclosure also is provided when it is reasonably possible that a loss will be incurred or when it is reasonably possible that the amount of a loss will exceed the recorded provision. The Company reviews the status of each significant matter and assesses its potential financial exposure. Significant judgment is required in both the determination of probability and the determination as to whether an exposure is reasonably estimable. Because of uncertainties related to these matters, accruals are based only on the best information available at the time. As additional information becomes available, the Company reassesses the potential liability related to pending claims and may change its estimates. These changes in the estimates of the potential liabilities could have a material impact on the Company’s condensed consolidated results of operations and financial position.

Recently Adopted Accounting Pronouncements

In May 2017, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update (“ASU”) 2017-09, Compensation—Stock Compensation (Topic 718): Scope of Modification Accounting (“ASU 2017-09”). ASC 2017-09 provides guidance about which changes to the terms or conditions of a share-based payment award require an entity to apply modification accounting in Topic 718. The Company adopted this standard in the first quarter of 2018 and its adoption did not have any impact on the Company’s condensed consolidated financial statements.

In November 2016, the FASB issued ASU 2016-18, Statement of Cash Flows (“ASU 2016-18”), which requires that amounts generally described as restricted cash and restricted cash equivalents should be included with cash and cash equivalents. The Company adopted this standard in the first quarter of 2018 and its adoption resulted in the inclusion of restricted cash in total cash and cash equivalents in the determination of changes in cash and cash equivalents in the Company’s condensed consolidated statements of cash flows. The presentation of restricted cash on the condensed consolidated balance sheet remains the same.

A reconciliation of the amounts from the cash flow statement to the balance sheet is as follows:


	March 31, 2018		March 31, 2017
Cash and cash equivalents as presented on balance sheet	$	164,773	$	29,266
Restricted cash, current, as presented on balance sheet		65		—
Restricted cash, non-current, as presented on balance sheet		237		165

Cash and cash equivalents and restricted cash as presented on cash flow statement	$	165,075	$	29,431

In August 2016, the FASB issued ASU 2016-15, Statement of Cash Flows (Topic 230): Classification of Certain Cash Receipts and Cash Payments (“ASU 2016-15”). ASU 2016-15 reduces diversity in practice by providing guidance on the classification of certain cash receipts and payments in the statement of cash flows. ASU 2016-15 clarifies that when cash receipts and cash payments have aspects of more than one class of cash flows and cannot be separated, classification will depend on the predominant source or use. ASU 2016-15 is effective on a retrospective basis. The Company adopted this standard in the first quarter of 2018 and the adoption of this standard did not have a material impact on the Company’s condensed consolidated statements of cash flows.

Recently Issued Accounting Pronouncements

In February 2016, the FASB issued ASU 2016-02, Leases (Topic 842) (“ASU 2016-02”), which sets out the principles for the recognition, measurement, presentation and disclosure of leases for both parties to a contract (i.e., lessees and lessors). The new standard requires lessees to apply a dual approach, classifying leases as either finance or operating leases based on the principle of whether or not the lease is effectively a financed purchase by the lessee. This classification will determine whether lease expense is recognized based on an effective interest method or on a straight-line basis over the term of the lease, respectively. A lessee is also required to record a right-of-use asset and a lease liability for all leases with a term of greater than 12 months regardless of their classification. Leases with a term of 12 months or less will be accounted for similar to existing guidance for operating leases today. ASU 2016-02 supersedes the previous leases standard, ASC 840, Leases. The standard is effective for public entities for annual periods beginning after December 15, 2018 and for interim periods within those fiscal years. Early adoption is permitted. The Company is currently evaluating the impact that the adoption of ASU 2016-02 will have on its condensed consolidated financial statements.

Merger and Recapitalization

3 Months Ended

Mar. 31, 2018

Business Combinations [Abstract]

Merger and Recapitalization

3. Merger and Recapitalization

On March 29, 2017, Solid Biosciences, LLC completed a series of transactions, which included the issuance of Series 1 Senior Preferred Units pursuant to the Senior Preferred Unit Purchase Agreement (the “Senior Preferred Unit Purchase Agreement”) and the merger of Solid GT into Solid Biosciences, LLC pursuant to the merger agreement between Solid Biosciences, LLC and Solid GT (the “Merger Agreement”), collectively referred to as the “Merger and Recapitalization.” As part of the Merger and Recapitalization, Solid Biosciences, LLC (a) issued 2,500,000 Series 1 Senior Preferred Units to new investors at $10.00 per unit resulting in gross proceeds to Solid Biosciences, LLC of $25,000, (b) merged operations of Solid GT into Solid Biosciences, LLC, effected through the exchange of Solid GT units held by non-controlling interests of Solid Biosciences, LLC into new classes Solid Biosciences, LLC units, and (c) exchanged existing Redeemable Preferred Units and Series A Common Units of Solid Biosciences, LLC into new units. The details of each component of the Merger and Recapitalization are as follows:

(a) Issuance of Series 1 Senior Preferred Units

Pursuant to the Senior Preferred Unit Purchase Agreement, Solid Biosciences, LLC issued 2,500,000 Series 1 Senior Preferred Units to new investors at $10.00 per unit resulting in gross proceeds to Solid Biosciences, LLC of $25,000.

(b) Merger of Solid GT into Solid Biosciences, LLC

Prior to the Merger and Recapitalization, Solid Biosciences, LLC issued Class B Non-Voting and Class D Voting Units of Solid GT to holders which represent non-controlling interests of Solid Biosciences, LLC. On March 29, 2017, in connection with the Merger and Recapitalization, the non-controlling interests were eliminated as follows:

•

50,000 Class B Non-Voting Units of Solid GT (“Solid GT Class B Units”) were exchanged for 1,635,916 Series C Common Units of Solid Biosciences, LLC; and

•

134,920 Class D Voting Units of Solid GT (“Solid GT Class D Units”) were exchanged for 4,414,356 Junior Preferred Units of Solid Biosciences, LLC.

In addition, the Class C Non-Voting Units of Solid GT (“Solid GT Class C Restricted Units”) were exchanged for Series D Common Units of Solid Biosciences, LLC. The Solid GT Class C Restricted Units were held by employees and consultants of Solid GT.

Since there was no change in control in connection with the Solid GT merger, the exchange of Solid GT Class B Units, Class C Restricted Units and Class D Units was accounted for as an equity transaction. In addition, because Solid GT Class D Units represented preferred units with preference over the other classes of Solid GT Units, the difference between the carrying value of the Solid GT Class D Units and the fair value of Junior Preferred Units was recorded as a deemed dividend in members’ deficit, which impacted net loss attributable to common unitholders.

(c) Exchange of Solid Biosciences, LLC existing Redeemable Preferred Units and Series A Common Units

In connection with the Merger and Recapitalization, Solid Biosciences, LLC exchanged its existing Redeemable Preferred Units and Series A Common Units as follows:

•

17,100,000 Redeemable Preferred Units of Solid Biosciences, LLC were exchanged for 12,219,299 Series A Common Units of Solid Biosciences, LLC.

•

4,560,000 Series A Common Units of Solid Biosciences, LLC were exchanged for 3,258,480 Series B Common Units of Solid Biosciences, LLC.

•

563,917 Series A Common Units of Solid Biosciences, LLC were exchanged for 402,963 Series D Common Units of Solid Biosciences, LLC.

The table below displays the pre-merger and post-merger capitalization structure of Solid Biosciences, LLC:

Pre-Merger and Recapitalization

Post-Merger and Recapitalization

Entity

Class

Issued

Entity

Class

Issued

Company

Redeemable Preferred

17,100,000

Company

Series A Common

12,219,299

Company

Series A Common (Founders)

4,560,000

Company

Series B Common

3,258,480

Company

Series A Common (Others)

563,917

Company

Series D Common

402,963

Solid GT

Class A Voting

450,000

Ceased to exist

Solid GT

Class B Non-Voting

50,000

Company

Series C Common

1,635,916

Solid GT

Class C Non-Voting

33,107

Company

Series D Common

1,083,205

Solid GT

Class D Voting

134,920

Company

Junior Preferred

4,414,356

Company (Total)

Common Units (Series A)

5,123,917

Company (Total)

Common Units

(Series A, B, C and D)

18,599,863

Fair Value of Financial Assets and Liabilities

3 Months Ended

Mar. 31, 2018

Fair Value Disclosures [Abstract]

Fair Value of Financial Assets and Liabilities

4. 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 March 31, 2018 Using:
	Level 1		Level 2		Level 3		Total
Assets:
Available-for-sale securities	$	—	$	17,609	$	—	$	17,609


	Fair Value Measurements as of December 31, 2017 Using:
	Level 1		Level 2		Level 3		Total
Assets:
Available-for-sale securities	$	—	$	17,014	$	—	$	17,014

As of March 31, 2018 and December 31, 2017, the fair values of the Company’s available-for-sale debt securities, which consisted of U.S. government agency securities and corporate bond securities, were determined using Level 2 inputs. During the three months ended March 31, 2018 and the year ended December 31, 2017, 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

3 Months Ended

Mar. 31, 2018

Investments, Debt and Equity Securities [Abstract]

Available-for-Sale Securities

5. Available-for-Sale Securities

As of March 31, 2018 and December 31, 2017, the fair value of available-for-sale securities by type of security was as follows:


	March 31, 2018
	Amortized Cost		Gross Unrealized Gain		Gross Unrealized Loss			Fair Value
Investments:
U.S. government agency securities	$	10,475	$	—	$	(9	)	$	10,466
Corporate bond securities		7,157		—		(14	)		7,143

	$	17,632	$	—	$	(23	)	$	17,609


	December 31, 2017
	Amortized Cost		Gross Unrealized Gain		Gross Unrealized Loss			Fair Value
Investments:
U.S. government agency securities	$	9,473	$	—	$	(7	)	$	9,466
Corporate bond securities		7,554		—		(6	)		7,548

	$	17,027	$	—	$	(13	)	$	17,014

The estimated fair value and amortized cost of the Company’s available-for-sale securities by contractual maturity are summarized as follows:


	March 31, 2018				December 31, 2017
	Amortized Cost		Fair Value		Amortized Cost		Fair Value
Due in one year or less	$	17,632	$	17,609	$	17,027	$	17,014

Total available-for-sale securities	$	17,632	$	17,609	$	17,027	$	17,014

The weighted average maturity of the Company’s available-for-sale securities as of March 31, 2018 and December 31, 2017 was approximately 0.4 years.

Property and Equipment

3 Months Ended

Mar. 31, 2018

Property, Plant and Equipment [Abstract]

Property and Equipment

6. Property and Equipment

Property and equipment consists of the following:


	March 31, 2018		December 31, 2017
Furniture and fixtures	$	66	$	61
Laboratory equipment		2,682		2,338
Leasehold improvements		84		68
Computer equipment		166		77
Computer software		23		23
Construction in process		2,128		366

		5,149		2,933
Less accumulated depreciation		731		504

	$	4,418	$	2,429

Depreciation expense was $227 and $51 for the three months ended March 31, 2018 and 2017, respectively.

Accrued Expenses and Other Current Liabilities

3 Months Ended

Mar. 31, 2018

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:


	March 31, 2018		December 31, 2017
Accrued research and development	$	996	$	1,855
Accrued compensation		979		2,033
Deferred funding from charitable organizations		213		233
Accrued other		1,904		2,084

	$	4,092	$	6,205

Equity-Based Compensation

3 Months Ended

Mar. 31, 2018

Disclosure of Compensation Related Costs, Share-based Payments [Abstract]

Equity-Based Compensation

8. Equity-Based Compensation

2018 Omnibus Incentive Plan

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. The following table summarizes the Company’s stock option activity for the three months ended March 31, 2018:


	Number of Options		Weighted Average Exercise Price
Outstanding at December 31, 2017		—	$	—
Granted		558,105		26.23

Outstanding at March 31, 2018		558,105	$	26.23

Exercisable at March 31, 2018		—	$	—

At March 31, 2018, the Company had an aggregate of $9,563 of unrecognized equity-based compensation cost related to stock options, which is expected to be recognized over a weighted average period of 3.9 years.

The fair value of each option award is estimated on the date of grant using the Black-Scholes option-pricing model using the assumptions noted in the following table:


	Three Months Ended March 31, 2018
Expected volatility		73.8	%
Expected dividends		0.00	%
Expected term (in years)		6.25
Risk-free rate		2.77	%

The weighted average fair value of options to purchase shares of common stock granted during the three months ended March 31, 2018 was $17.68.

Restricted Common Stock

In connection with the Company’s Corporate Conversion on January 25, 2018, all restricted Series B and D common units were converted to restricted shares of common stock. The following table summarizes the Company’s unvested restricted shares of common stock activity from December 31, 2017 through March 31, 2018:


	Units / Shares			Weighted- Average Grant Date Fair Value
Unvested restricted Series D Common Units at December 31, 2017		1,404,265		$	4.83
Vested units prior to Corporate Conversion		(66,019	)		3.46
Forfeited units prior to Corporate Conversion		(8,932	)		2.99
Unvested Series D Common Units at January 25, 2018 prior to Corporate Conversion		1,329,314			4.91

Conversion to restricted shares of common stock upon Corporate Conversion		1,128,182			5.79
Vested shares of common stock		(56,655	)		3.93
Forfeited		(6,042	)		5.55

Unvested restricted shares of common stock at March 31, 2018		1,065,485		$	5.89

At March 31, 2018, the Company had an aggregate of $5,655 of unrecognized equity-based compensation cost related to restricted shares of common stock, which is expected to be recognized over a weighted average period of 1.6 years.

The Company recorded equity-based compensation expense related to all of its share and unit-based awards to employees and non-employees in the following captions within its condensed consolidated statements of operations for the three months ended March 31:


	2018		2017
Research and development	$	632	$	393
General and administrative		187		2,837

Total	$	819	$	3,230

Income Taxes

3 Months Ended

Mar. 31, 2018

Income Tax Disclosure [Abstract]

Income Taxes

9. Income Taxes

The Company recorded no tax benefit for the three months ended March 31, 2018 for the net operating losses incurred due to its uncertainty of realizing a benefit from those items. The Company was not subject to federal and state income taxes for the three months ended March 31, 2017 as it was organized as a limited liability company which was taxed as a partnership for U.S. tax purposes.

A reconciliation of income taxes computed using the U.S. federal statutory rate to that reflected in operations as of March 31, 2018 is as follows:


	March 31, 2018
Income tax computed at federal statutory tax rate		21.0	%
State taxes, net of federal benefit		3.1	%
Permanent differences		(2.3	)%
Tax credits		6.4	%
Loss taxed as a partnership		(8.2	)%
Other		(0.1	)%
Valuation allowance		(19.9	)%

		0.0	%

The Company established deferred tax assets and liabilities on identified book to tax temporary differences as of the date of conversion to a C-corporation. Deferred income taxes reflect the net tax effects of these temporary differences between the carrying amounts of assets and liabilities for financial reporting purposes and the amounts used for income tax purposes. Significant components of the Company’s net deferred tax assets as of March 31, 2018 is as follows:


	March 31, 2018
Deferred tax assets:
Tax loss carryforwards	$	2,027
Tax credit carryforwards		1,019
Intangible assets		108
Deferred revenues		58
Deferred expenses		100
Accrued expenses		188
Other		9

Total deferred tax assets		3,509

Depreciation		(224	)
Valuation allowance		(3,285	)

Net deferred taxes	$	—

As of March 31, 2018, the Company has federal net operating loss carryforwards of $6,935 and tax credits of $956 which may be used to offset future federal income and tax liability, respectively. In addition, the Company has state net operating loss carryforwards of approximately $6,922 and tax credits of $80 which may be used to offset future state income and tax liability, respectively. The Company’s ability to utilize these federal and state carryforwards may be limited in the future if the Company experiences an ownership change pursuant to Internal Revenue Code Section 382. Ownership changes, as defined in the Internal Revenue Code, including those resulting from the issuance of common stock in connection with the Company’s public offerings, may limit the amount of net operating loss and tax credit carryforwards that can be utilized to offset future taxable income or tax liability. The Company has not conducted a study to assess whether a change of control has occurred or whether there have been multiple changes of control since inception due to the significant complexity and cost associated with such a study. If the Company has experienced a change of control, as defined by Section 382, at any time since inception, utilization of the net operating loss carryforwards or research and development tax credit carryforwards would be subject to an annual limitation under Section 382. Any limitation may result in expiration of a portion of the net operating loss carryforwards or research and development tax credit carryforwards before utilization. Further, until a study is completed and any limitation is known, no amounts are being presented as an uncertain tax position.

A valuation allowance is recorded against deferred tax assets if it is more likely than not that some or all of the deferred tax assets will not be realized. The Company has evaluated the positive and negative evidence bearing upon the realizability of the deferred tax assets. The Company concluded, in accordance with the applicable accounting standards, that it is more likely than not that the Company will not realize the benefit of its deferred tax assets. Accordingly, the Company has recorded a full valuation allowance against its deferred tax assets. The Company had approximately $3,285 in valuation allowances recorded against its deferred tax assets as of March 31, 2018.

As of March 31, 2018, the Company did not have unrecognized tax benefits. The Company recognizes interest and penalties related to income taxes as a component of income tax expense. As of March 31, 2018, no interest and penalties have been recorded.

Commitments and Contingencies

3 Months Ended

Mar. 31, 2018

Commitments and Contingencies Disclosure [Abstract]

Commitments and Contingencies

10. Commitments and Contingencies

Contingencies

In the first quarter of 2017, the Company terminated the development, manufacturing and testing agreement (the “Agreement”) it entered into in January 2016 with a third-party. The Company and the third-party were in dispute regarding the remaining amounts owned by the Company to the third-party under the Agreement. The Company settled the matter in April 2018 for $1,320. This amount is included in accrued expenses and other liabilities at March 31, 2018.

Legal Proceedings

On March 27, 2018, a purported stockholder of the Company, filed a putative class action complaint alleging violations of the federal securities laws, in the United States District Court for the District of Massachusetts (Case No. 18-10587), against the Company and certain of the Company’s current executive officers and underwriters in the Company’s initial public offering. The plaintiff claims to represent purchasers of the Company’s common stock during the period from January 25, 2018 to March 14, 2018 and seeks unspecified damages arising out of the alleged failure to disclose risks associated with toxicity and potential for adverse events related to the Company’s lead product candidate.

On March 28, 2018, a purported stockholder of the Company, filed a putative class action complaint alleging violations of the federal securities laws, in the Business Litigation Section of the Superior Court of the Commonwealth of Massachusetts (Civil Action No. 1884-00984), against the Company, Ilan Ganot, Jennifer Ziolkowski, the Company’s directors and certain of the underwriters in the Company’s initial public offering. The plaintiff in this suit claims to represent purchasers of the Company’s common stock in or traceable to the Company’s January 25, 2018 initial public offering and seeks unspecified damages arising out of the alleged failure to disclose risks associated with toxicity and potential for adverse events related to the Company’s lead product candidate.

On April 3, 2018, a purported stockholder of the Company, filed a putative class action complaint alleging violations of the federal securities laws, in the United States District Court for the District of Massachusetts (Case No. 18-10639), against the Company, Ilan Ganot and Jennifer Ziolkowski. The plaintiff in this suit claims to represent purchasers of the Company’s common stock during the period from January 25, 2018 to March 14, 2018 and seeks unspecified damages arising out of the alleged failure to disclose risks associated with toxicity and potential for adverse events related to the Company’s lead product candidate.

While the Company is vigorously defending against all claims asserted, this litigation could result in substantial costs to the Company and a diversion of the Company’s management’s attention and resources, which could harm its business. In addition, the uncertainty of the pending lawsuits or potential filing of additional lawsuits could lead to more volatility and a reduction in the Company’s stock price. Given the early stage of the litigation, at this time the Company is unable to reasonably estimate possible losses or form a judgment that an unfavorable outcome is either probable or remote. It is not currently possible to assess whether or not the outcome of these proceedings may have a material adverse effect on the Company.

Leases

In January 2018, the Company executed a lease agreement for lab space in Cambridge, Massachusetts. The lease consists of approximately 9,500 square feet with an initial term of five years with the option to extend the term for one additional two year term. The future minimum rent commitment for the initial five-year term is approximately $3,800. In addition to rent, the lease requires the Company to pay additional amounts for taxes, insurance, maintenance and other operating expenses.

In January 2018, the Company executed a lease agreement for office space in Cambridge, Massachusetts. The space serves as the Company’s corporate headquarters and consists of approximately 16,000 square feet. The term of the lease runs through February 2022. The future minimum rent commitment for the lease term is approximately $4,600. In addition to rent, the lease requires the Company to pay additional amounts for taxes, insurance, maintenance and other operating expenses.

Future minimum lease payments for these operating leases as of March 31, 2018 were as follows:


Year Ending December 31,
2018	$	1,157
2019		1,917
2020		1,999
2021		2,038
2022		1,005
Thereafter		267

Total	$	8,383

Net Loss per Share

3 Months Ended

Mar. 31, 2018

Earnings Per Share [Abstract]

Net Loss per Share

11. 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 for the three months ended March 31:


	2018			2017
Net loss	$	(15,877	)	$	(13,875	)
Net loss attributable to non-controlling interest		—			(1,060	)

Net loss attributable to Solid Biosciences Inc.	$	(15,877	)	$	(12,815	)
Accretion of preferred units to redemption value		—			(959	)
Redemption of preferred units		—			15,685
Redemption of redeemable interest from non-controlling interest in Solid GT		—			(1,925	)

Net loss attributable to common stockholders	$	(15,877	)	$	(14	)

The denominator is as follows for the three months ended March 31:


	2018		2017
Weighted average shares of common stock outstanding, basic and diluted		29,354,650		3,047,759

Net loss per share attributable to common stockholders, basic and diluted is as follows for the three months ended March 31:


	2018			2017
Net loss per share attributable to common stockholders	$	(0.54	)	$	(0.01	)

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 months ended March 31:


	2018		2017
Options to purchase shares of common stock		558,105		—
Unvested shares of common stock		1,065,485		—
Series B common units		—		814,620
Series D common units		—		819,578

		1,623,590		1,634,198

Summary of Significant Accounting Policies (Policies)

3 Months Ended

Mar. 31, 2018

Accounting Policies [Abstract]

Use of Estimates

Use of 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

Available-for-Sale Securities

Available-for-Sale Securities

Concentration of Credit Risk and of Significant Suppliers

Concentration of Credit Risk and of Significant Suppliers

Fair Value Measurements

Fair Value Measurements

•

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

•

Equity-Based Compensation

Equity-Based Compensation

Income Taxes

Income Taxes

Prior to the January 25, 2018, the Company had not been subject to U.S. federal income taxes as the Company was organized as limited liability company. As such, the taxable income or loss was passed through to and included in the tax returns of the members. Since January 25, 2018, the Company’s income has since been subject to U.S. federal, state, local, and foreign income taxes and taxed at the prevailing corporate tax rates.

Segment Data

Segment Data

Comprehensive Loss

Comprehensive Loss

Net Loss per Share

Net Loss per Share

Contingencies

Contingencies

Recently Adopted Accounting Pronouncements

Recently Adopted Accounting Pronouncements

A reconciliation of the amounts from the cash flow statement to the balance sheet is as follows:


	March 31, 2018		March 31, 2017
Cash and cash equivalents as presented on balance sheet	$	164,773	$	29,266
Restricted cash, current, as presented on balance sheet		65		—
Restricted cash, non-current, as presented on balance sheet		237		165

Cash and cash equivalents and restricted cash as presented on cash flow statement	$	165,075	$	29,431

Recently Issued Accounting Pronouncements

Recently Issued Accounting Pronouncements

Summary of Significant Accounting Policies (Tables)

3 Months Ended

Mar. 31, 2018

Accounting Policies [Abstract]

Reconciliation of Amounts From Cash Flow Statement to Balance Sheet

A reconciliation of the amounts from the cash flow statement to the balance sheet is as follows:


	March 31, 2018		March 31, 2017
Cash and cash equivalents as presented on balance sheet	$	164,773	$	29,266
Restricted cash, current, as presented on balance sheet		65		—
Restricted cash, non-current, as presented on balance sheet		237		165

Cash and cash equivalents and restricted cash as presented on cash flow statement	$	165,075	$	29,431

Merger and Recapitalization (Tables)

3 Months Ended

Mar. 31, 2018

Business Combinations [Abstract]

Schedule of Pre-Merger and Post-Merger Capitalization Structure

The table below displays the pre-merger and post-merger capitalization structure of Solid Biosciences, LLC:

Pre-Merger and Recapitalization

Post-Merger and Recapitalization

Entity

Class

Issued

Entity

Class

Issued

Company

Redeemable Preferred

17,100,000

Company

Series A Common

12,219,299

Company

Series A Common (Founders)

4,560,000

Company

Series B Common

3,258,480

Company

Series A Common (Others)

563,917

Company

Series D Common

402,963

Solid GT

Class A Voting

450,000

Ceased to exist

Solid GT

Class B Non-Voting

50,000

Company

Series C Common

1,635,916

Solid GT

Class C Non-Voting

33,107

Company

Series D Common

1,083,205

Solid GT

Class D Voting

134,920

Company

Junior Preferred

4,414,356

Company (Total)

Common Units (Series A)

5,123,917

Company (Total)

Common Units

(Series A, B, C and D)

18,599,863

Fair Value of Financial Assets and Liabilities (Tables)

3 Months Ended

Mar. 31, 2018

Fair Value Disclosures [Abstract]

Summary of Assets and Liabilities Measured at Fair Value on Recurring Basis and Indicate Level of Fair Value Hierarchy Utilized


	Fair Value Measurements as of March 31, 2018 Using:
	Level 1		Level 2		Level 3		Total
Assets:
Available-for-sale securities	$	—	$	17,609	$	—	$	17,609


	Fair Value Measurements as of December 31, 2017 Using:
	Level 1		Level 2		Level 3		Total
Assets:
Available-for-sale securities	$	—	$	17,014	$	—	$	17,014

Available-for-Sale Securities (Tables)

3 Months Ended

Mar. 31, 2018

Investments, Debt and Equity Securities [Abstract]

Schedule of Fair Value of Available-for-Sale Securities by Type of Security

As of March 31, 2018 and December 31, 2017, the fair value of available-for-sale securities by type of security was as follows:


	March 31, 2018
	Amortized Cost		Gross Unrealized Gain		Gross Unrealized Loss			Fair Value
Investments:
U.S. government agency securities	$	10,475	$	—	$	(9	)	$	10,466
Corporate bond securities		7,157		—		(14	)		7,143

	$	17,632	$	—	$	(23	)	$	17,609


	December 31, 2017
	Amortized Cost		Gross Unrealized Gain		Gross Unrealized Loss			Fair Value
Investments:
U.S. government agency securities	$	9,473	$	—	$	(7	)	$	9,466
Corporate bond securities		7,554		—		(6	)		7,548

	$	17,027	$	—	$	(13	)	$	17,014

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:


	March 31, 2018				December 31, 2017
	Amortized Cost		Fair Value		Amortized Cost		Fair Value
Due in one year or less	$	17,632	$	17,609	$	17,027	$	17,014

Total available-for-sale securities	$	17,632	$	17,609	$	17,027	$	17,014

- Definition

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

+ References + Details

Property and Equipment (Tables)

3 Months Ended

Mar. 31, 2018

Property, Plant and Equipment [Abstract]

Summary of Property and Equipment

Property and equipment consists of the following:


	March 31, 2018		December 31, 2017
Furniture and fixtures	$	66	$	61
Laboratory equipment		2,682		2,338
Leasehold improvements		84		68
Computer equipment		166		77
Computer software		23		23
Construction in process		2,128		366

		5,149		2,933
Less accumulated depreciation		731		504

	$	4,418	$	2,429

Accrued Expenses and Other Current Liabilities (Tables)

3 Months Ended

Mar. 31, 2018

Payables and Accruals [Abstract]

Summary of Accrued Expenses and Other Current Liabilities

Accrued expenses and other current liabilities consist of the following:


	March 31, 2018		December 31, 2017
Accrued research and development	$	996	$	1,855
Accrued compensation		979		2,033
Deferred funding from charitable organizations		213		233
Accrued other		1,904		2,084

	$	4,092	$	6,205

Equity-Based Compensation (Tables)

3 Months Ended

Mar. 31, 2018

Disclosure of Compensation Related Costs, Share-based Payments [Abstract]

Summary of Stock Option Activity

The following table summarizes the Company’s stock option activity for the three months ended March 31, 2018:


	Number of Options		Weighted Average Exercise Price
Outstanding at December 31, 2017		—	$	—
Granted		558,105		26.23

Outstanding at March 31, 2018		558,105	$	26.23

Exercisable at March 31, 2018		—	$	—

Assumptions for Measuring Fair Values of Stock Options

The fair value of each option award is estimated on the date of grant using the Black-Scholes option-pricing model using the assumptions noted in the following table:


	Three Months Ended March 31, 2018
Expected volatility		73.8	%
Expected dividends		0.00	%
Expected term (in years)		6.25
Risk-free rate		2.77	%

Schedule of Unvested Restricted Shares of Common Stock Activity

The following table summarizes the Company’s unvested restricted shares of common stock activity from December 31, 2017 through March 31, 2018:


	Units / Shares			Weighted- Average Grant Date Fair Value
Unvested restricted Series D Common Units at December 31, 2017		1,404,265		$	4.83
Vested units prior to Corporate Conversion		(66,019	)		3.46
Forfeited units prior to Corporate Conversion		(8,932	)		2.99
Unvested Series D Common Units at January 25, 2018 prior to Corporate Conversion		1,329,314			4.91

Conversion to restricted shares of common stock upon Corporate Conversion		1,128,182			5.79
Vested shares of common stock		(56,655	)		3.93
Forfeited		(6,042	)		5.55

Unvested restricted shares of common stock at March 31, 2018		1,065,485		$	5.89

Schedule of Equity-based Compensation Expense


	2018		2017
Research and development	$	632	$	393
General and administrative		187		2,837

Total	$	819	$	3,230

Income Taxes (Tables)

3 Months Ended

Mar. 31, 2018

Income Tax Disclosure [Abstract]

Schedule of Reconciliation of Income Taxes Computed by U.S. Federal Statutory Rate

A reconciliation of income taxes computed using the U.S. federal statutory rate to that reflected in operations as of March 31, 2018 is as follows:


	March 31, 2018
Income tax computed at federal statutory tax rate		21.0	%
State taxes, net of federal benefit		3.1	%
Permanent differences		(2.3	)%
Tax credits		6.4	%
Loss taxed as a partnership		(8.2	)%
Other		(0.1	)%
Valuation allowance		(19.9	)%

		0.0	%

Schedule of Net Deferred Tax Assets

Significant components of the Company’s net deferred tax assets as of March 31, 2018 is as follows:


	March 31, 2018
Deferred tax assets:
Tax loss carryforwards	$	2,027
Tax credit carryforwards		1,019
Intangible assets		108
Deferred revenues		58
Deferred expenses		100
Accrued expenses		188
Other		9

Total deferred tax assets		3,509

Depreciation		(224	)
Valuation allowance		(3,285	)

Net deferred taxes	$	—

Commitments and Contingencies (Tables)

3 Months Ended

Mar. 31, 2018

Commitments and Contingencies Disclosure [Abstract]

Summary of Future Minimum Lease Payments for Operating Leases

Future minimum lease payments for these operating leases as of March 31, 2018 were as follows:


Year Ending December 31,
2018	$	1,157
2019		1,917
2020		1,999
2021		2,038
2022		1,005
Thereafter		267

Total	$	8,383

Net Loss per Share (Tables)

3 Months Ended

Mar. 31, 2018

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 for the three months ended March 31:


	2018			2017
Net loss	$	(15,877	)	$	(13,875	)
Net loss attributable to non-controlling interest		—			(1,060	)

Net loss attributable to Solid Biosciences Inc.	$	(15,877	)	$	(12,815	)
Accretion of preferred units to redemption value		—			(959	)
Redemption of preferred units		—			15,685
Redemption of redeemable interest from non-controlling interest in Solid GT		—			(1,925	)

Net loss attributable to common stockholders	$	(15,877	)	$	(14	)

The denominator is as follows for the three months ended March 31:


	2018		2017
Weighted average shares of common stock outstanding, basic and diluted		29,354,650		3,047,759

Net loss per share attributable to common stockholders, basic and diluted is as follows for the three months ended March 31:


	2018			2017
Net loss per share attributable to common stockholders	$	(0.54	)	$	(0.01	)

Schedule of Antidilutive Securities Excluded from Calculation of Diluted Net Loss per Share Attributable to Common Stockholders


	2018		2017
Options to purchase shares of common stock		558,105		—
Unvested shares of common stock		1,065,485		—
Series B common units		—		814,620
Series D common units		—		819,578

		1,623,590		1,634,198

Nature of the Business and Basis of Presentation - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands		1 Months Ended	3 Months Ended
	Jan. 30, 2018	Nov. 30, 2015	Mar. 31, 2018	Mar. 31, 2017	Jan. 25, 2018	Dec. 31, 2017
Nature Of Business And Basis Of Presentation [Line Items]
Net loss			$ (15,877)	$ (13,875)
Accumulated deficit			140,135			$ 124,258
Cash, cash equivalents and available-for-sale securities			$ 182,382
Net loss attributable to non-controlling interest				(1,060)
Corporate Conversion [Member]
Nature Of Business And Basis Of Presentation [Line Items]
Common stock, conversion basis			One for 0.8485 basis
Common stock, conversion ratio					84.85%
Solid GT, LLC [Member]
Nature Of Business And Basis Of Presentation [Line Items]
Voting ownership percentage before transactions		100.00%
Voting ownership percentage after transactions		77.00%
Net loss attributable to non-controlling interest			$ 0	$ (1,060)
IPO [Member]
Nature Of Business And Basis Of Presentation [Line Items]
Number of shares sold	8,984,375
Public offering price per share	$ 16.00
Net proceeds from issuance	$ 129,096

Summary of Significant Accounting Policies - Additional Information (Detail) - USD ($)	3 Months Ended
	Mar. 31, 2018	Dec. 31, 2017	Mar. 31, 2017
Significant Accounting Policies [Line Items]
Restricted cash deposit	$ 302,000	$ 65,000
Restricted cash	65,000	$ 65,000
Restricted cash noncurrent	237,000		$ 165,000
Income tax expense (benefit)	$ 0
2018 Omnibus Incentive Plan [Member]
Significant Accounting Policies [Line Items]
Number of shares authorized for common stock for equity awards	5,001,000

Summary of Significant Accounting Policies - Reconciliation of Amounts From Cash Flow Statement to Balance Sheet (Detail) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017	Mar. 31, 2017	Dec. 31, 2016
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	$ 164,773	$ 52,080	$ 29,266
Restricted cash, current, as presented on balance sheet	65	65
Restricted cash, non-current, as presented on balance sheet	237		165
Cash and cash equivalents and restricted cash as presented on cash flow statement	$ 165,075	$ 52,145	$ 29,431	$ 7,843

Merger and Recapitalization - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands			12 Months Ended
	Mar. 29, 2017	Mar. 28, 2017	Dec. 31, 2017
Series C Common Units in Exchange for Class B Non-controlling Interest in Solid GT [Member]
Schedule of Capitalization [Line Items]
Common units exchanged, units		50,000
Issuance of common units in exchange, units	1,635,916
Series A Common Units in Exchange for Redeemable Preferred Units [Member]
Schedule of Capitalization [Line Items]
Issuance of common units in exchange, units	12,219,299
Series B Common Units in exchange for Series A Common Units [Member]
Schedule of Capitalization [Line Items]
Common units exchanged, units		4,560,000
Issuance of common units in exchange, units	3,258,480
Series D Common Units in Exchange for Series A Common Units [Member]
Schedule of Capitalization [Line Items]
Common units exchanged, units		563,917
Issuance of common units in exchange, units	402,963
Series 1 Senior Preferred Units [Member]
Schedule of Capitalization [Line Items]
Issuance of preferred units, units	2,500,000		2,500,000
Preferred units, price per unit	$ 10.00
Proceeds from issuance of units	$ 25,000
Junior Preferred Units [Member]
Schedule of Capitalization [Line Items]
Issuance of preferred units, units	4,414,356		4,414,356
Redeemable Preferred Units [Member]
Schedule of Capitalization [Line Items]
Issuance of Series A common units in exchange for redeemable preferred units, units		17,100,000	17,100,000
Solid GT, LLC [Member] \| Series D Common Units [Member]
Schedule of Capitalization [Line Items]
Common units exchanged, units		134,920

Merger and Recapitalization - Schedule of Pre-Merger And Post-Merger Capitalization Structure (Detail) - shares	Mar. 31, 2018	Dec. 31, 2017	Mar. 29, 2017	Mar. 28, 2017
Schedule of Capitalization [Line Items]
Common Units Issued	0	19,438,552
Series A Common Units [Member]
Schedule of Capitalization [Line Items]
Common Units Issued			12,219,299	5,123,917
Series A Common Units [Member] \| Solid GT, LLC [Member]
Schedule of Capitalization [Line Items]
Common Units Issued				450,000
Series A Common Units [Member] \| Founders Of Company [Member]
Schedule of Capitalization [Line Items]
Common Units Issued				4,560,000
Series A Common Units [Member] \| Other Management Employees [Member]
Schedule of Capitalization [Line Items]
Common Units Issued				563,917
Series B Common Units [Member]
Schedule of Capitalization [Line Items]
Common Units Issued			3,258,480
Series B Common Units [Member] \| Solid GT, LLC [Member]
Schedule of Capitalization [Line Items]
Common Units Issued				50,000
Series D Common Units One [Member]
Schedule of Capitalization [Line Items]
Common Units Issued			402,963
Series C- Common Units [Member]
Schedule of Capitalization [Line Items]
Common Units Issued			1,635,916
Series C- Common Units [Member] \| Solid GT, LLC [Member]
Schedule of Capitalization [Line Items]
Common Units Issued				33,107
Series D Common Units Two [Member]
Schedule of Capitalization [Line Items]
Common Units Issued			1,083,205
Series A, B, C and D Common Units [Member]
Schedule of Capitalization [Line Items]
Common Units Issued			18,599,863
Series D Common Units [Member] \| Solid GT, LLC [Member]
Schedule of Capitalization [Line Items]
Common Units Issued				134,920
Junior Preferred Units [Member]
Schedule of Capitalization [Line Items]
Preferred Units Issued	0	4,414,356	4,414,356
Redeemable Preferred Units [Member]
Schedule of Capitalization [Line Items]
Preferred Units Issued				17,100,000

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 ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Assets:
Available-for-sale securities	$ 17,609	$ 17,014
Level 2 [Member]
Assets:
Available-for-sale securities	$ 17,609	$ 17,014

Fair Value of Financial Assets and Liabilities - Additional Information (Detail) - USD ($)	Mar. 31, 2018	Dec. 31, 2017
Fair Value Disclosures [Abstract]
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, level 3 to level 1 transfers, amount	0	0
Fair value, assets, level 1 to level 3 transfers, amount	$ 0	$ 0

Available-for-Sale Securities - Schedule of Fair Value of Available-for-Sale Securities by Type of Security (Detail) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 17,632	$ 17,027
Gross Unrealized Gain	0	0
Gross Unrealized Loss	(23)	(13)
Fair Value	17,609	17,014
U.S. Government Agency Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	10,475	9,473
Gross Unrealized Gain	0	0
Gross Unrealized Loss	(9)	(7)
Fair Value	10,466	9,466
Corporate Bond Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	7,157	7,554
Gross Unrealized Gain	0	0
Gross Unrealized Loss	(14)	(6)
Fair Value	$ 7,143	$ 7,548

Available-for-Sale Securities - Summary Estimated Fair Value and Amortized Cost of Available-for-Sale Securities by Contractual Maturity (Detail) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Investments, Debt and Equity Securities [Abstract]
Due in one year or less, amortized cost	$ 17,632	$ 17,027
Total available-for-sale securities, amortized cost	17,632	17,027
Due in one year or less, fair value	17,609	17,014
Total available-for-sale securities, fair value	$ 17,609	$ 17,014

Available-for-Sale Securities - Additional Information (Detail)	3 Months Ended	12 Months Ended
	Mar. 31, 2018	Dec. 31, 2017
Investments, Debt and Equity Securities [Abstract]
Available-for-sale securities weighted average maturity period	4 months 24 days	4 months 24 days

Property and Equipment - Summary of Property and Equipment (Detail) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 5,149	$ 2,933
Less accumulated depreciation	731	504
Property and equipment, net	4,418	2,429
Furniture and Fixtures [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	66	61
Laboratory Equipment [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	2,682	2,338
Leasehold Improvements [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	84	68
Computer Equipment [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	166	77
Computer Software [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	23	23
Construction in Progress [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 2,128	$ 366

Property and Equipment - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Property, Plant and Equipment [Abstract]
Depreciation expense	$ 227	$ 51

Accrued Expenses and Other Current Liabilities - Summary of Accrued Expenses and Other Current Liabilities (Detail) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Accrued Expenses And Other Current Liabilities [Line Items]
Accrued expenses and other current liabilities	$ 4,092	$ 6,205
Accrued Research and Development [Member]
Accrued Expenses And Other Current Liabilities [Line Items]
Accrued expenses and other current liabilities	996	1,855
Accrued Compensation [Member]
Accrued Expenses And Other Current Liabilities [Line Items]
Accrued expenses and other current liabilities	979	2,033
Deferred Funding from Charitable Organizations [Member]
Accrued Expenses And Other Current Liabilities [Line Items]
Accrued expenses and other current liabilities	213	233
Accrued Other [Member]
Accrued Expenses And Other Current Liabilities [Line Items]
Accrued expenses and other current liabilities	$ 1,904	$ 2,084

Equity-Based Compensation - Additional Information (Detail) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2018 USD ($) $ / shares shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized equity-based compensation cost related to stock options	$ 9,563
Unrecognized equity-based compensation cost related to stock options, period for recognition	3 years 10 months 25 days
Weighted average fair value of options to purchase common stock granted \| $ / shares	$ 17.68
Restricted Common Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized equity-based compensation cost related to stock options, period for recognition	1 year 7 months 6 days
Unrecognized equity-based compensation cost	$ 5,655
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 \| shares	5,001,000

Equity-Based Compensation - Summary of Stock Option Activity (Detail)	3 Months Ended
	Mar. 31, 2018 $ / shares shares
Shares
Granted \| shares	558,105
Outstanding at March 31, 2018 \| shares	558,105
Exercisable at March 31, 2018 \| shares	0
Weighted Average per share price
Granted \| $ / shares	$ 26.23
Outstanding at March 31, 2018 \| $ / shares	26.23
Exercisable at March 31, 2018 \| $ / shares	$ 0

Equity-Based Compensation - Assumptions for Measuring Fair Values of Stock Options (Detail)	3 Months Ended
	Mar. 31, 2018
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Expected volatility	73.80%
Expected dividends	0.00%
Expected term (in years)	6 years 3 months
Risk-free rate	2.77%

Equity-Based Compensation - Schedule of Unvested Restricted Shares of Common Stock Activity (Detail) - Restricted Common Stock [Member]	3 Months Ended
	Mar. 31, 2018 $ / shares shares
Units / Shares
Unvested restricted Series D Common Units at December 31, 2017 \| shares	1,404,265
Vested units prior to Corporate Conversion \| shares	(66,019)
Forfeited units prior to Corporate Conversion \| shares	(8,932)
Unvested Series D Common Units at January 25, 2018 prior to Corporate Conversion \| shares	1,329,314
Conversion to restricted shares of common stock upon Corporate Conversion \| shares	1,128,182
Vested shares of common stock \| shares	(56,655)
Forfeited \| shares	(6,042)
Unvested restricted shares of common stock at March 31, 2018 \| shares	1,065,485
Weighted-Average Grant Date Fair Value
Unvested restricted Series D Common Units at December 31, 2017 \| $ / shares	$ 4.83
Vested units prior to Corporate Conversion \| $ / shares	3.46
Forfeited units prior to Corporate Conversion \| $ / shares	2.99
Unvested series D Common Units at January 25, 2018 prior to Corporate Conversion \| $ / shares	4.91
Conversion to restricted shares of common stock upon Corporate Conversion \| $ / shares	5.79
Vested shares of common stock \| $ / shares	3.93
Forfeited \| $ / shares	5.55
Unvested restricted shares of common stock at March 31, 2018 \| $ / shares	$ 5.89

Equity-Based Compensation - Schedule of Equity-based Compensation Expense (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	$ 819	$ 3,230
Research and Development [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	632	393
Selling, General and Administrative [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	$ 187	$ 2,837

Income Taxes - Additional Information (Detail)	3 Months Ended
Income Taxes - Additional Information (Detail)	Mar. 31, 2018 USD ($)
Income Taxes [Line Items]
Income tax expense (benefit)	$ 0
Uncertain tax position	0
Deferred tax assets, valuation allowances	3,285,000
Unrecognized tax benefits	0
Tax interest and penalties	0
Domestic Tax Authority [Member]
Income Taxes [Line Items]
Net operating loss carryforwards	6,935,000
Federal tax credits carryforwards	956,000
State and Local Jurisdiction [Member]
Income Taxes [Line Items]
Net operating loss carryforwards	6,922,000
Federal tax credits carryforwards	$ 80,000

Income Taxes - Schedule of Reconciliation of Income Taxes Computed by U.S. Federal Statutory Rate (Detail)	3 Months Ended
	Mar. 31, 2018
Income Tax Disclosure [Abstract]
Income tax computed at federal statutory tax rate	21.00%
State taxes, net of federal benefit	3.10%
Permanent differences	(2.30%)
Tax credits	6.40%
Loss taxed as a partnership	(8.20%)
Other	(0.10%)
Valuation allowance	(19.90%)
Total	0.00%

Income Taxes - Schedule of Net Deferred Tax Assets (Detail) $ in Thousands	Mar. 31, 2018 USD ($)
Deferred tax assets:
Tax loss carryforwards	$ 2,027
Tax credit carryforwards	1,019
Intangible assets	108
Deferred revenues	58
Deferred expenses	100
Accrued expenses	188
Other	9
Total deferred tax assets	3,509
Depreciation	(224)
Valuation allowance	(3,285)
Net deferred taxes	$ 0

Commitments and Contingencies - Additional Information (Detail) $ in Thousands		1 Months Ended	3 Months Ended
	Apr. 30, 2018 USD ($)	Jan. 31, 2018 USD ($) ft²	Mar. 31, 2018 USD ($)
Commitment And Contingencies [Line Items]
Future minimum rent commitment			$ 8,383
Lab Space In Cambridge Massachusetts [Member]
Commitment And Contingencies [Line Items]
Area of lease agreement \| ft²		9,500
Lease term		5 years
Lease renewal term		2 years
Future minimum rent commitment		$ 3,800
Office Space In Cambridge Massachusetts [Member]
Commitment And Contingencies [Line Items]
Area of lease agreement \| ft²		16,000
Future minimum rent commitment		$ 4,600
Lease expiration period		2022-02
Accrued Expenses and Other Current Liabilities [Member]
Commitment And Contingencies [Line Items]
Contingency settled amount			$ 1,320
Subsequent Event [Member]
Commitment And Contingencies [Line Items]
Contingency settled amount to third-party, under agreement	$ 1,320

Commitments and Contingencies - Summary of Future Minimum Lease Payments for Operating Leases (Detail) $ in Thousands	Mar. 31, 2018 USD ($)
Operating Leases, Future Minimum Payments Due, Fiscal Year Maturity [Abstract]
2018	$ 1,157
2019	1,917
2020	1,999
2021	2,038
2022	1,005
Thereafter	267
Total	$ 8,383

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		12 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Earnings Per Share [Abstract]
Net loss	$ (15,877)	$ (13,875)
Net loss attributable to non-controlling interest		(1,060)
Net loss attributable to Solid Biosciences Inc.	(15,877)	(12,815)	$ (53,178)
Accretion of preferred units to redemption value		(959)
Redemption of preferred units		15,685
Redemption of redeemable interest from non-controlling interest in Solid GT		(1,925)
Net loss attributable to common stockholders	$ (15,877)	$ (14)
Weighted average shares of common stock outstanding, basic and diluted	29,354,650	3,047,759
Net loss per share attributable to common stockholders	$ (0.54)	$ (0.01)

Net Loss per Share - Schedule of Antidilutive Securities Excluded from Calculation of Diluted Net Loss per Share Attributable to Common Stockholders (Detail) - shares	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Common stock / unit equivalents excluded from calculation of diluted net loss per share / unit	1,623,590	1,634,198
Options to Purchase Shares of Common Stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Common stock / unit equivalents excluded from calculation of diluted net loss per share / unit	558,105
Unvested Shares of Common Stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Common stock / unit equivalents excluded from calculation of diluted net loss per share / unit	1,065,485
Series B Common Units [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Common stock / unit equivalents excluded from calculation of diluted net loss per share / unit		814,620
Series D Common Units [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Common stock / unit equivalents excluded from calculation of diluted net loss per share / unit		819,578