Eiger BioPharmaceuticals (EIGRQ) S-4 14 Dec 15 Registration of securities issued in business combination transactions Financial data

Document and Entity Information

Document and Entity Information	9 Months Ended
	Sep. 30, 2015
Document And Entity Information [Abstract]
Document Type	S4
Amendment Flag	false
Document Period End Date	Sep. 30, 2015
Trading Symbol	CLDN
Entity Registrant Name	Celladon Corp
Entity Central Index Key	1,305,253
Entity Filer Category	Non-accelerated Filer

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014	Dec. 31, 2013
Current assets:
Cash and cash equivalents	$ 37,092	$ 14,435	$ 7,903
Short-term investments		70,513	10,467
Prepaid expenses and other assets	1,001	3,135	180
Total current assets	38,093	88,083	18,550
Property and equipment, net	133	763	308
Other assets	10	264	2,296
Total assets	38,236	89,110	21,154
Current liabilities:
Accounts payable and accrued expenses	1,025	5,803	2,908
Accrued restructuring charges	609
Accrued clinical expenses	163	731	1,478
Accrued interest		71	14
Current portion of long-term obligations		1
Convertible notes, net of discount			1,044
Warrant liability			1,116
Total current liabilities	1,797	6,606	6,560
Long-term obligations, net of discount		10,102
Non-current liabilities	$ 29	$ 298	$ 37
Commitments and contingencies
Stockholders' equity (deficit):
Preferred stock
Common stock	$ 24	$ 23
Additional paid-in capital	222,492	218,528	$ 61,593
Accumulated other comprehensive (loss) income		(8)	2
Accumulated deficit	(186,106)	(146,439)	(112,586)
Stockholders' equity:	36,410	72,104	(50,991)
Total liabilities and stockholders' equity	$ 38,236	89,110	21,154
Series A-1 Redeemable Convertible Preferred Stock [Member]
Stockholders' equity (deficit):
Preferred stock, value		0	60,098
Convertible Preferred Stock [Member]
Stockholders' equity (deficit):
Preferred stock, value		$ 0	$ 5,450

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014	Dec. 31, 2013
Preferred stock, shares authorized			147,964,577
Preferred stock, shares outstanding			139,278,610
Preferred stock, liquidation preference			$ 119,622
Preferred stock, par value	$ 0.001	$ 0.001	$ 0.001
Preferred stock, shares authorized	10,000,000	10,000,000	0
Preferred stock, shares issued	0	0	0
Preferred stock, shares outstanding	0	0	0
Common stock, par value	$ 0.001	$ 0.001	$ 0.001
Common stock, shares authorized	200,000,000	200,000,000	180,000,000
Common stock, shares issued	23,916,021	23,490,737	884,179
Common stock, shares outstanding	23,916,021	23,490,737	884,179
Series A-1 Redeemable Convertible Preferred Stock [Member]
Preferred stock, par value		$ 0.0001	$ 0.0001
Preferred stock, shares authorized		0	135,826,497
Preferred stock, shares issued		0	127,140,530
Preferred stock, shares outstanding		0	127,140,530
Preferred stock, liquidation preference		$ 0	$ 114,172
Convertible Preferred Stock [Member]
Preferred stock, par value		$ 0.0001	$ 0.0001
Preferred stock, shares authorized		0	12,138,080
Preferred stock, shares issued		0	12,138,080
Preferred stock, shares outstanding		0	12,138,080
Preferred stock, liquidation preference		$ 0	$ 5,450

Consolidated Statements of Oper

Consolidated Statements of Operations and Comprehensive Loss - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Operating expenses:
Research and development	$ 738	$ 5,316	$ 21,757	$ 15,515	$ 22,676	$ 16,927	$ 13,314
General and administrative	2,533	2,815	10,805	6,545	10,342	3,037	2,631
Restructuring charges	1,781		4,862
Total operating expenses	5,052	8,131	37,424	22,060	33,018	19,964	15,945
Loss from operations	(5,052)	(8,131)	(37,424)	(22,060)	(33,018)	(19,964)	(15,945)
Other income (expense):
Interest income	6	36	60	65	118	69	35
Interest expense	(1,347)	(271)	(2,302)	(330)	(741)	(59)	(108)
Other income (expense)	(3)	8	(1)	(4)	(29)	25	147
Change in fair value of warrant liability				(183)	(183)	(162)
Consolidated net loss	(6,396)	(8,358)	(39,667)	(22,512)	(33,853)	(20,091)	(15,871)
Net loss attributable to non-controlling interest						96	154
Net loss attributable to Celladon Corporation					(33,853)	(19,995)	(15,717)
Accretion to redemption value of redeemable convertible preferred stock							(343)
Change in fair value of non-controlling interest						(3,105)	(154)
Deemed dividend						(856)
Net loss attributable to common stockholders					(33,853)	(23,956)	(16,214)
Other comprehensive loss:
Unrealized (loss) gain on investments		(26)	8	(10)	(10)	(7)	9
Comprehensive loss	$ (6,396)	$ (8,384)	$ (39,659)	$ (22,522)	$ (33,863)	$ (20,098)	$ (15,862)
Net loss per share attributable to common stockholders, basic and diluted	$ (0.27)	$ (0.40)	$ (1.66)	$ (1.32)	$ (1.82)	$ (27.09)	$ (19.74)
Weighted-average shares outstanding, basic and diluted	23,915,361	20,752,895	23,830,668	16,999,766	18,603,605	884,179	821,568

Consolidated Statements of Pref

Consolidated Statements of Preferred Stock and Stockholders' Deficit - USD ($) $ in Thousands	Total	Series A-1 Redeemable Convertible Preferred Stock [Member]	Convertible Preferred Stock [Member]	Initial Public Offering [Member]	Initial Public Offering [Member]Series A-1 Redeemable Convertible Preferred Stock [Member]	Initial Public Offering [Member]Convertible Preferred Stock [Member]	Special Voting Stock [Member]	Common Stock [Member]	Common Stock [Member]Initial Public Offering [Member]	Additional Paid-in Capital [Member]	Additional Paid-in Capital [Member]Initial Public Offering [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Accumulated Deficit [Member]
Temporary equity, Beginning balance at Dec. 31, 2011			$ 56,282
Temporary equity, Beginning balance, Shares at Dec. 31, 2011			39,186,807
Conversion of convertible securities into stock, Temporary equity value			$ (56,282)
Conversion of convertible securities into stock, Temporary equity shares			(39,186,807)
Conversion of convertible securities into stock, Temporary equity value		$ 6,807	$ 5,450
Issuance of Series A-1 preferred stock, net of $343 of offering costs, Temporary equity		$ 45,124
Issuance of Series A-1 preferred stock, net of $343 of offering costs, Temporary equity shares		101,263,824
Accretion to redemption value of redeemable convertible preferred stock, Temporary equity shares		$ 343
Temporary equity, Ending balance at Dec. 31, 2012		$ 52,274	$ 5,450
Temporary equity, Ending balance, Shares at Dec. 31, 2012		116,424,125	12,138,080
Beginning Balance at Dec. 31, 2011	$ (70,979)							$ 5,895					$ (76,874)
Impact of initial public offering
Conversion of convertible securities into stock	2,188							$ 2,188
Conversion of convertible securities into stock, Shares								849,952
Beginning Balance, Shares at Dec. 31, 2011								2,798
Impact of initial public offering
Issuance of common stock	0						$ 0	$ 0		$ 0		$ 0	0
Issuance of common stock, Shares								55
Conversion of Series A, B, B-1 and C preferred stock to common stock	56,282							$ 56,282
Conversion of Series A, B, B-1 and C preferred stock to common stock, Shares								31,374
Conversion of convertible securities into stock	2,188							$ 2,188
Conversion of convertible securities into stock, Shares								849,952
Delaware reincorporation								$ (64,168)		64,168
Issuance of special voting stock							$ 1
Issuance of special voting stock, Shares							1
Accretion to redemption value of redeemable convertible preferred stock	(343)							(252)		(91)
Stock-based compensation	298							$ 55		243
Change in fair value of redeemable non-controlling interest	(154)									(154)
Consolidated net loss	(15,871)												(15,871)
Net loss attributable to redeemable non-controlling interest	154												154
Unrealized gain (loss) on investment securities	9											9
Ending Balance at Dec. 31, 2012	$ (28,416)									64,166		9	(92,591)
Ending Balance, Shares at Dec. 31, 2012								884,179
Conversion of convertible securities into stock, Temporary equity shares		15,160,301	12,138,080
Share exchange related to non-controlling interest and special voting stock		$ 7,824
Share exchange related to non-controlling interest and special voting stock, Temporary equity, Shares		10,716,405
Temporary equity, Ending balance at Dec. 31, 2013		$ 60,098	$ 5,450
Temporary equity, Ending balance, Shares at Dec. 31, 2013	139,278,610	127,140,530	12,138,080
Impact of initial public offering
Stock-based compensation	$ 1,388									1,388
Change in fair value of redeemable non-controlling interest	(3,105)									(3,105)
Share exchange related to non-controlling interest and special voting stock							$ (1)
Share exchange related to non-controlling interest and special voting stock, Shares							(1)
Deemed dividend	(856)									(856)
Consolidated net loss	(20,091)												(20,091)
Net loss attributable to redeemable non-controlling interest	96												96
Unrealized gain (loss) on investment securities	(7)											(7)
Ending Balance at Dec. 31, 2013	$ (50,991)									61,593		2	(112,586)
Ending Balance, Shares at Dec. 31, 2013	884,179							884,179
Common stock issuance upon exercise of warrants	$ 143									143
Common stock issuance upon exercise of warrants, Shares								25,481
Conversion of convertible securities into stock, Temporary equity value					$ (60,098)	$ (5,450)
Public offering of common stock, net	40,689			$ 44,258				$ 5	$ 6	40,684	$ 44,252
Conversion of convertible securities into stock, Temporary equity shares					(127,140,530)	(12,138,080)
Public offering of common stock, net, Shares								4,600,000	6,325,000
Temporary equity, Ending balance at Dec. 31, 2014		$ 0	$ 0
Temporary equity, Ending balance, Shares at Dec. 31, 2014		0	0
Impact of initial public offering
Public offering of common stock, net	40,689			44,258				$ 5	$ 6	40,684	44,252
Public offering of common stock, net, Shares								4,600,000	6,325,000
Conversion of convertible notes into common stock				1,117							1,117
Conversion of convertible notes into common stock, shares									139,644
Conversion of convertible securities into stock				65,548					$ 11		65,537
Conversion of convertible securities into stock, Shares									11,151,192
Warrant liability reclassification				1,299							1,299
Conversion of convertible securities into stock				$ 65,548					$ 11		$ 65,537
Conversion of convertible securities into stock, Shares									11,151,192
Stock-based compensation	3,319									3,319
Exercise of stock options	$ 407							$ 1		406
Exercise of stock options, Shares	340,220							340,220
Issuance of common stock under employee stock purchase plan	$ 178									178
Issuance of common stock under employee stock purchase plan, Shares								25,021
Consolidated net loss	(33,853)												(33,853)
Unrealized gain (loss) on investment securities	(10)											(10)
Ending Balance at Dec. 31, 2014	$ 72,104							$ 23		$ 218,528		$ (8)	$ (146,439)
Ending Balance, Shares at Dec. 31, 2014	23,490,737							23,490,737
Impact of initial public offering
Consolidated net loss	$ (39,667)
Unrealized gain (loss) on investment securities	8
Ending Balance at Sep. 30, 2015	$ 36,410
Ending Balance, Shares at Sep. 30, 2015	23,916,021

Consolidated Statements of Pre6

Consolidated Statements of Preferred Stock and Stockholders' Deficit (Parenthetical) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2012
Issuance of Series A-1 preferred stock, net of offering costs		$ 343
Public offering of common stock, offering costs	$ 3,011
Initial Public Offering [Member]
Public offering of common stock, offering costs	$ 6,342

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	9 Months Ended		12 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Cash flows from operating activities
Consolidated net loss	$ (39,667)	$ (22,512)	$ (33,853)	$ (20,091)	$ (15,871)
Adjustments to reconcile net loss to net cash used in operating activities
Depreciation	371	110	153	67	64
Asset impairments	192
Stock-based compensation	3,183	2,178	3,319	1,388	298
Noncash interest expense	1,807	190	388	59	108
Amortization of investment premium	194	163	393	255	124
Change in fair value of warrant liability		183	183	162
Loss on disposal of property and equipment	2	1	1
Deferred rent	(117)	84	74	17	28
Changes in operating assets and liabilities:
Prepaid expenses and other assets	2,239	(689)	(2,860)	104	(266)
Accounts payable and accrued expenses	(4,937)	910	2,935	1,843	878
Other liabilities		8	8
Net cash used in operating activities	(36,733)	(19,374)	(29,259)	(16,196)	(14,637)
Cash flows from investing activities
Purchases of investment securities		(88,661)	(90,659)	(17,860)	(26,751)
Proceeds from maturities of investment securities	70,327	18,200	30,210	28,801	4,966
Purchases of property and equipment	(235)	(549)	(739)	(87)	(48)
Proceeds from sale of property and equipment	277
Net cash provided by (used in) investing activities	70,369	(71,010)	(61,188)	10,854	(21,833)
Cash flows from financing activities
Proceeds from issuance of common stock	783	94,578	95,028
Proceeds from issuance of preferred stock, net					45,140
Proceeds from issuance of exchangeable shares					4,814
Proceeds from issuance of convertible debt				1,097
Repayment of convertible debt	(10,000)				(111)
Costs paid in connection with common stock offering		(7,396)	(7,661)	(1,693)
Proceeds from borrowing under term loan		10,000	10,000
Costs paid in connection with term loan	(1,750)	(334)	(387)
Other	(12)		(1)
Net cash provided by (used in) financing activities	(10,979)	96,848	96,979	(596)	49,843
Net increase (decrease) in cash and cash equivalents	22,657	6,464	6,532	(5,938)	13,373
Cash and cash equivalents, beginning of period	14,435	7,903	7,903	13,841	468
Cash and cash equivalents, end of period	$ 37,092	$ 14,367	14,435	7,903	13,841
Supplemental disclosure of cash flow information
Interest paid			282
Supplemental schedule of noncash investing and financing activities
Share exchange related to non-controlling interest and special voting stock				7,824
Deemed dividend				856
Accrued purchases of property and equipment			23	$ 166
Warrant liability reclassification to equity			1,299
Capital expenditures funded by capital lease borrowings			12
Common Stock [Member]
Supplemental schedule of noncash investing and financing activities
Conversion of convertible debt and accrued interest and convertible notes			1,117
Series A-1 and Junior Preferred and Common Stock [Member]
Supplemental schedule of noncash investing and financing activities
Conversion of convertible debt and accrued interest and convertible notes					$ 14,430
Convertible Preferred Stock [Member]
Supplemental schedule of noncash investing and financing activities
Conversion of convertible preferred stock into common stock			$ 65,548

Basis of Presentation, Organiza

Basis of Presentation, Organization and Summary of Significant Accounting Policies	9 Months Ended	12 Months Ended
	Sep. 30, 2015	Dec. 31, 2014
Accounting Policies [Abstract]
Basis of Presentation, Organization and Summary of Significant Accounting Policies	1. Basis of Presentation, Organization and Summary of Significant Accounting Policies Basis of Presentation The accompanying unaudited consolidated financial statements of Celladon Corporation (Celladon or the Company) should be read in conjunction with the audited financial statements and notes thereto as of and for the year ended December 31, 2014 included in the Company’s Annual Report on Form 10-K (Annual Report) filed with the Securities and Exchange Commission (SEC). The accompanying financial statements have been prepared in accordance with U.S. generally accepted accounting principles (GAAP) for interim financial information and in accordance with the instructions to Form 10-Q and Article 10 of Regulation S-X. Accordingly, since they are interim statements, the accompanying financial statements do not include all of the information and notes required by GAAP for complete financial statements. In the opinion of management, the accompanying financial statements reflect all adjustments (consisting of normal recurring adjustments) that are necessary for a fair statement of the financial position, results of operations and cash flows for the interim periods presented. Interim results are not necessarily indicative of results for a full year. The preparation of the Company’s consolidated financial statements requires it to make estimates and assumptions that impact the reported amounts of assets, liabilities and expenses and the disclosure of contingent assets and liabilities in the Company’s consolidated financial statements and accompanying notes. The most significant estimates in the Company’s consolidated financial statements relate to the fair value of equity awards and clinical trial expense accruals. Although these estimates are based on the Company’s knowledge of current events and actions it may undertake in the future, actual results may ultimately materially differ from these estimates and assumptions. Organization Celladon was incorporated in California on December 21, 2000 (inception) and reincorporated in Delaware in April 2012. The Company is a biotechnology company that has been focused on the development of cardiovascular gene therapy. As a consequence of the negative results from the Phase 2b clinical trial of its lead product candidate, MYDICAR (AAV1/SERCA2a), the Company is evaluating its strategic opportunities to maximize shareholder value, including the possibility of seeking a merger, sale of the Company or all or some of its assets, and/or a liquidation. At this time, the Company’s current development activities are limited to the oversight of the long-term follow up period in the CUPID 2 trial, which is expected to continue through February 2016. As of September 30, 2015, the Company has devoted substantially all of its efforts to product development, raising capital and building infrastructure and has not generated revenues from product sales or other sources. Principles of Consolidation The financial statements of the Company’s former subsidiary Celladon Europe B.V. (Celladon Europe) were consolidated with those of the Company through Celladon Europe’s dissolution on December 30, 2014. All intercompany transactions and balances were eliminated in consolidation. Investment Securities Investment securities primarily consist of investment grade corporate debt securities. The Company classifies all investment securities as available-for-sale. Investments with maturity dates greater than 12 months from the end of each reporting period are classified as long-term. Investment securities are carried at fair value, with the unrealized gains and losses reported as a component of other comprehensive income (loss) in stockholders’ equity (deficit) until realized. Realized gains and losses from the sale of investment securities, if any, are determined on a specific identification basis. A decline in the market value of any investment security below cost that is determined to be other than temporary will result in an impairment charge to earnings and a new cost basis for the security is established. No such impairment charges were recorded for any period presented. As of December 31, 2014, none of the investment securities had been in an unrealized loss position for more than 12 months. Premiums and discounts are amortized or accreted over the life of the related security as an adjustment to yield using the straight-line method and are included in interest income. Interest income is recognized when earned. During the third quarter of 2015 the Company’s investment securities matured and the Company held the proceeds as cash equivalents. As of September 30, 2015, the Company had no investment securities. The following table sets forth the composition of the Company’s investment securities (in thousands) as of December 31, 2014: Unrealized As of December 31, 2014 Maturity in Years Amortized Gains Losses Fair Corporate debt securities Less than 1 year $ 70,521 $ — $ (8 ) $ 70,513 Net Loss Per Share Attributable to Common Stockholders Basic and diluted net loss per common share is calculated by dividing net loss applicable to common stockholders by the weighted-average number of common shares outstanding during the period, without consideration for common stock equivalents. Potentially dilutive shares, which include convertible preferred stock and rights to acquire convertible preferred stock (non-controlling interest), warrants for the purchase of common stock and options outstanding under the Company’s equity incentive plans, are considered to be common stock equivalents and are only included in the calculation of diluted net loss per share when their effect is dilutive. Potentially dilutive securities not included in the calculation of diluted net loss per share attributable to common stockholders because to do so would be anti-dilutive are as follows (in common stock equivalent shares): Nine Months Ended 2015 2014 Warrants for common stock 152,735 206,340 Common stock options and restricted stock units 1,527,098 2,527,067 1,679,833 2,733,407 Recent Accounting Pronouncements In April 2015, the Financial Accounting Standards Board (the “FASB”) issued Accounting Standards Update (“ASU”) No. 2015-03, Interest - Imputation of Interest (Subtopic 835-30): Simplifying the Presentation of Debt Issuance Costs. The amendments in this ASU require that debt issuance costs related to a recognized debt liability be presented in the balance sheet as a direct deduction from the carrying amount of that debt liability, consistent with debt discounts. The amendments in this ASU are effective for financial statements issued for fiscal years beginning after December 15, 2015, and interim periods within those fiscal years. Early adoption of the amendments is permitted. The new guidance shall be applied on a retrospective basis, wherein the balance sheet of each individual period presented should be adjusted to reflect the period-specific effects of applying the new guidance. The Company is currently evaluating the impact of the adoption of this standard on its consolidated financial statements. In August 2014, the FASB issued ASU 2014-15, which defined management’s responsibility to evaluate whether there is substantial doubt about an entity’s ability to continue as a going concern and to provide related disclosure. ASU 2014-15 defined the term substantial doubt and requires an assessment for a period of one year after the date of the issuance of the financial statements. It requires certain disclosures when substantial doubt is alleviated as a result of consideration of management’s plans and requires an express statement and other disclosures when substantial doubt is not alleviated. The guidance becomes effective for reporting periods beginning after December 15, 2016, with early adoption permitted. The Company does not believe that the adoption of this guidance will have a material impact on its consolidated financial statements.	1. Organization and Summary of Significant Accounting Policies Organization Celladon Corporation (Celladon or the Company) was incorporated in California on December 21, 2000 (inception) and reincorporated in Delaware in April 2012. The Company is a clinical-stage biotechnology with industry-leading expertise in the development of cardiovascular gene therapy. The Company applies its leadership position in the field of gene therapy and calcium dysregulation to develop novel therapies for diseases with tremendous unmet medical needs and characterized by an underlying SERCA enzyme deficiency. As of December 31, 2014, the Company has devoted substantially all of its efforts to product development, raising capital and building infrastructure and has not generated revenues from its planned principal operations. Use of Estimates The Company’s consolidated financial statements are prepared in accordance with U.S. generally accepted accounting principles (GAAP). The preparation of the Company’s consolidated financial statements requires it to make estimates and assumptions that impact the reported amounts of assets, liabilities and expenses and the disclosure of contingent assets and liabilities in the Company’s consolidated financial statements and accompanying notes. The most significant estimates in the Company’s consolidated financial statements relate to the fair value of equity awards and clinical trial expense accruals. Although these estimates are based on the Company’s knowledge of current events and actions it may undertake in the future, actual results may ultimately materially differ from these estimates Public Offerings In February 2014, the Company completed its initial public offering of 6,325,000 shares of common stock at an offering price of $8.00 per share, which included the exercise by the underwriters of their option to purchase 825,000 additional shares of common stock. The Company received net proceeds of $44.3 million after deducting underwriting discounts and commission and offering expenses payable by the Company, including $1.7 million in offering costs paid by the Company prior to December 31, 2013. In connection with the initial public offering, all outstanding shares of convertible preferred stock were converted into shares of common stock, the outstanding principal and accrued interest on the Company’s outstanding convertible notes were converted into shares of common stock and the unamortized debt discount related to the convertible notes was charged to expense, warrants to purchase shares of Series A-1 preferred stock were converted into warrants to purchase common stock, the warrant liability was reclassified to additional paid-in capital, and the Company’s certificate of incorporation was amended and restated to authorize 200,000,000 shares of common stock and 10,000,000 shares of undesignated preferred stock. See Note 7 for additional information. In August 2014, the Company completed an underwritten public offering of 4,600,000 shares of common stock at an offering price of $9.50 per share, which included the exercise by the underwriters of their option to purchase 600,000 additional shares of common stock. The Company received net proceeds of $40.7 million after deducting underwriting discounts and commission and offering expenses payable by the Company. See Note 7 for additional information. Principles of Consolidation On April 27, 2012, Celladon formed a subsidiary, Celladon Europe B.V. (Celladon Europe), a Dutch limited liability company, for the purpose of managing the new capital investment made by Cooperatief LSP IV U.A. (LSP) related to Celladon’s Series A-1 preferred stock (see Note 2). From its inception to June 6, 2013 the subsidiary was 90% owned by Celladon and from June 6, 2013 to December 29, 2014 the subsidiary was wholly owned by Celladon. Celladon Europe was dissolved on December 30, 2014. The financial statements of Celladon Europe are consolidated with those of the Company. All intercompany transactions and balances were eliminated in consolidation. The U.S. dollar was the functional currency of Celladon Europe. The Company remeasured Celladon Europe’s assets and liabilities related to monetary assets and liabilities to the U.S. dollar and recorded the net gains or losses resulting from remeasurement in other income (expense) in the consolidated statements of operations and comprehensive loss. During all periods presented, the Company did not record any material gains or losses from remeasurement. Segment Reporting Operating segments are identified as components of an enterprise about which separate discrete financial information is available for evaluation by the chief operating decision-maker in making decisions regarding resource allocation and assessing performance. The Company views its operations and manages its business in one operating segment. Cash and Cash Equivalents Cash and cash equivalents consists primarily of readily available checking, money market accounts and money market funds. The Company considers all highly liquid investments with an original maturity of three months or less at the date of purchase to be cash equivalents. Investment Securities Investment securities primarily consist of investment grade corporate debt securities. The Company classifies all investment securities as available-for-sale. Investments with maturity dates greater than 12 months from the end of each reporting period are classified as long-term. Investment securities are carried at fair value, with the unrealized gains and losses reported as a component of other comprehensive income (loss) in stockholders’ equity (deficit) until realized. Realized gains and losses from the sale of investment securities, if any, are determined on a specific identification basis. A decline in the market value of any investment security below cost that is determined to be other than temporary will result in an impairment charge to earnings and a new cost basis for the security is established. No such impairment charges were recorded for any period presented. As of December 31, 2014 and December 31, 2013, none of the investment securities have been in an unrealized loss position for more than 12 months. Premiums and discounts are amortized or accreted over the life of the related security as an adjustment to yield using the straight-line method and are included in interest income. Interest income is recognized when earned. The following table sets forth the composition of the Company’s investment securities (in thousands): As of December 31, 2014 Maturity in Years Amortized Unrealized Fair Value Gains Losses Corporate debt securities Less than 1 year $ 70,521 $ — $ (8 ) $ 70,513 As of December 31, 2013 Maturity in Years Amortized Unrealized Fair Value Gains Losses Corporate debt securities Less than 1 year $ 10,465 $ 2 $ — $ 10,467 Concentration of Credit Risk Financial instruments, which potentially subject the Company to significant concentration of credit risk, consist primarily of cash, cash equivalents and investment securities. The Company has established guidelines regarding diversification of investments and their maturities, which are designed to maintain principal and maximize liquidity. The Company maintains deposits in federally insured financial institutions in excess of federally insured limits. The Company has not experienced any losses in such accounts and management believes that the Company is not exposed to significant credit risk due to the financial position of the depository institutions in which those deposits are held. Property and Equipment Property and equipment are recorded at cost and depreciated using the straight-line method over the estimated useful lives of the assets (generally three to five years) and generally consist of furniture and fixtures, computers, and office equipment. Repairs and maintenance costs are charged to expense as incurred. Impairment of Long-Lived Assets Long-lived assets consist primarily of property and equipment. An impairment loss is recorded if and when events and circumstances indicate that assets might be impaired and the undiscounted cash flows estimated to be generated by those assets are less than the carrying amount of those assets. While the Company’s current and historical operating losses and negative cash flows are indicators of impairment, management believes that future cash flows to be received support the carrying value of its long-lived assets and, accordingly, has not recognized any impairment losses since inception. Clinical Trial Accruals As part of the process of preparing its financial statements, the Company is required to estimate its expenses resulting from its obligations under contracts with vendors and consultants and clinical site agreements in connection with conducting clinical trials. The financial terms of these contracts are subject to negotiations which vary from contract to contract and may result in payment flows that do not match the periods over which materials or services are provided to the Company under such contracts. The Company’s objective is to reflect the appropriate trial expenses in its financial statements by matching those expenses with the period in which services and efforts are expended. The Company accounts for these expenses according to the progress of the trial as measured by patient progression and the timing of various aspects of the trial. The Company determines accrual estimates through financial models taking into account discussion with applicable personnel and outside service providers as to the progress or state of consummation of trials, or the services completed. During the course of a clinical trial, the Company adjusts its rate of clinical expense recognition if actual results differ from its estimates. The Company makes estimates of its accrued expenses as of each balance sheet date in its financial statements based on the facts and circumstances known at that time. Although the Company does not expect its estimates to be materially different from amounts actually incurred, its understanding of the status and timing of services performed relative to the actual status and timing of services performed may vary and may result in the Company reporting amounts that are too high or too low for any particular period. Through December 31, 2014, there have been no material adjustments to the Company’s prior period estimates of accrued expenses for clinical trials. The Company’s clinical trial accrual is dependent upon the timely and accurate reporting of contract research organizations and other third-party vendors. Preferred Stock Warrant Liability The Company had issued freestanding warrants to purchase shares of its convertible preferred stock. The fair value of these warrants is classified as a current liability at December 31, 2013 in the accompanying consolidated balance sheets since the underlying redeemable convertible preferred stock is classified as temporary equity at December 31, 2013 in the accompanying consolidated balance sheets instead of in stockholders’ equity (deficit) in accordance with authoritative guidance for the classification and measurement of redeemable securities. The warrants were recorded at fair value using the Black-Scholes option pricing model with any changes in fair value being recognized as a component of other income (expense) in the accompanying consolidated statements of operations and comprehensive loss. Upon completion of the Company’s initial public offering in February 2014, the warrants no longer required liability accounting and the then fair value of the warrant liability was reclassified into equity Deferred Rent Deferred rent consists of the difference between cash payments and the recognition of rent expense on a straight-line basis for the facility the Company occupies. The Company’s lease for its facility provides for fixed increases in minimum annual rental payments. The total amount of rental payments due over the lease term is being charged to rent expense ratably over the life of the lease. Preferred Stock The Company classifies preferred stock that is redeemable or subject to liquidation outside of the Company’s control outside of permanent equity. For preferred stock that is contractually redeemable outside of the Company’s control, the carrying value is increased to its redemption value by accretion in the period of issuance. In the absence of retained earnings, these accretion charges are recorded against additional paid-in capital. Research and Development Costs Research and development expenses consist primarily of salaries and related overhead expenses; fees paid to consultants and contract research organizations; costs related to acquiring and manufacturing clinical trial materials; costs related to compliance with regulatory requirements; and maintenance and license payments related to licensed product candidates and technologies. All research and development costs are expensed as incurred. Patent Costs Costs related to filing and pursuing patent applications are recorded as general and administrative expense and expensed as incurred since recoverability of such expenditures is uncertain. Stock-Based Compensation Stock-based compensation expense represents the cost of the grant date fair value of employee stock option grants and stock purchases under the Employee Stock Purchase Plan (ESPP) recognized over the requisite service period of the awards (usually the vesting period) on a straight-line basis, net of estimated forfeitures. The Company estimates the fair value of the awards using the Black-Scholes option pricing model. The Company accounts for stock options granted to non-employees using the fair value approach. These option grants are subject to periodic revaluation over their vesting terms. Income Taxes The Company accounts for income taxes under the asset and liability method, which requires the recognition of deferred tax assets and liabilities for the expected future tax consequences of events that have been included in the financial statements. Under this method, deferred tax assets and liabilities are determined on the basis of the differences between the financial statements and tax basis of assets and liabilities using enacted tax rates in effect for the year in which the differences are expected to reverse. The effect of a change in tax rates on deferred tax assets and liabilities is recognized in income in the period that includes the enactment date. The Company recognizes net deferred tax assets to the extent that management believes these assets are more likely than not to be realized. In making such a determination, management considers all available positive and negative evidence, including future reversals of existing taxable temporary differences, projected future taxable income, tax-planning strategies, and results of recent operations. If management determines that the Company would be able to realize its deferred tax assets in the future in excess of their net recorded amount, management would make an adjustment to the deferred tax asset valuation allowance, which would reduce the provision for income taxes. The Company records uncertain tax positions on the basis of a two-step process whereby (1) management determines whether it is more likely than not that the tax positions will be sustained on the basis of the technical merits of the position and (2) for those tax positions that meet the more-likely-than-not recognition threshold, management recognizes the largest amount of tax benefit that is more than 50% likely to be realized upon ultimate settlement with the related tax authority. The Company recognizes interest and penalties related to unrecognized tax benefits within income tax expense. Any accrued interest and penalties are included within the related tax liability. Comprehensive Loss Comprehensive loss is defined as a change in equity during a period from transactions and other events and circumstances from non-owner sources. The Company’s only component of other comprehensive loss is unrealized gains (losses) on investment securities. Comprehensive loss has been reflected in the consolidated statements of operations and comprehensive loss and as a separate component of the statements of stockholders’ deficit for all periods presented. Net Loss Per Share Attributable to Common Stockholders Basic net loss per share attributable to common stockholders is calculated by dividing the net loss attributable to common stockholders by the weighted-average number of common shares outstanding for the period, without consideration for common stock equivalents. Diluted 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 common share equivalents outstanding for the period determined using the treasury-stock method. Dilutive common stock equivalents are comprised of convertible preferred stock and rights to acquire convertible preferred stock (non-controlling interest), warrants for the purchase of common stock and options outstanding under the Company’s stock option plans. For all periods presented, there is no difference in the number of shares used to calculate basic and diluted shares outstanding due to the Company’s net loss position. Potentially dilutive securities not included in the calculation of diluted net loss per share attributable to common stockholders because to do so would be anti-dilutive are as follows (in common stock equivalent shares): Years Ended December 31, 2014 2013 Redeemable convertible preferred stock — 10,179,372 Convertible preferred stock — 971,820 Warrants for convertible preferred stock — 231,821 Warrants for common stock 206,340 702 Common stock options 2,408,634 1,543,667 2,614,974 12,927,382 Recent Accounting Pronouncements In July 2013, the FASB issued Accounting Standards Update (ASU) No. 2013-11, Presentation of an Unrecognized Tax Benefit When a Net Operating Loss Carryforward, a Similar Tax Loss, or a Tax Credit Carryforward Exists In June 2014, the FASB issued Accounting Standards Update (ASU) No. 2014-10, Development Stage Entities (Topic 915): Elimination of Certain Financial Reporting Requirements, Including an Amendment to Variable Interest Entities Guidance in Topic 810, Consolidation 810-10-15-16 development stage entities In June 2014, the FASB issued ASU No. 2014-12, Accounting for Share-Based Payments When the Terms of an Award Provide That a Performance Target Could Be Achieved after the Requisite Service Period In August 2014, the FASB issued ASU No. 2014-15, Presentation of Financial Statements Going Concern In November 2014, the FASB issued ASU No. 2014-16, Determining Whether the Host Contract in a Hybrid Financial Instrument Issued in the Form of a Share is More Akin to Debt or Equity

Celladon Europe B.V.

Celladon Europe B.V.	12 Months Ended
	Dec. 31, 2014
Equity Method Investments and Joint Ventures [Abstract]
Celladon Europe B.V.	2. Celladon Europe B.V. In April 2012 and June 2012, LSP invested an aggregate of $4.8 million in Celladon Europe. In exchange for the investment, the Company issued LSP one share of Special Preferred Voting stock and Celladon Europe issued LSP 1,999 non-voting B shares. The 1,999 B shares were exchangeable into 10,716,405 shares of the Company’s Series A-1 preferred stock at the option of LSP. The Company determined that the investment held by LSP in Celladon Europe should be classified as a redeemable non-controlling interest, as the shares of Celladon Europe were not in-substance common stock. In-substance common stock is an investment in an entity that has risk and reward characteristics that are substantially similar to that entity’s common stock. Due to the liability characteristics associated with the shares of Celladon Europe held by LSP, the Company concluded that the investor’s shares were not substantially similar to common stock. The liability characteristics included the investor’s put rights, which provided the investor with the ability to exchange its shares in Celladon Europe for Series A-1 preferred stock of the Company. The redeemable non-controlling interest was initially valued using the fair value of the Series A-1 preferred stock. At each reporting period, the Company adjusted the carrying value of the redeemable non-controlling interest by the net loss attributable to the redeemable non-controlling interest. Any difference between the fair value and the adjusted carrying value of the redeemable non-controlling interest was recorded as an adjustment to additional paid-in capital and presented as a component of net loss attributable to common stockholders in the accompanying consolidated statements of operations and comprehensive loss. From April 2012 through June 6, 2013, LSP owned approximately 10% of Celladon Europe. On June 6, 2013, LSP delivered a notice to exchange its 1,999 B shares of Celladon Europe for 10,716,405 shares of the Company’s Series A-1 preferred stock. Concurrently, the one share of outstanding Special Preferred Voting stock was cancelled. As of June 6, 2013, the redeemable non-controlling interest was adjusted to fair value and reclassified to Series A-1 preferred stock on the accompanying consolidated balance sheet. During the years ended December 31, 2013 and 2012, the Company adjusted the loss attributable to common stockholders as a result of increases in the fair value of the redeemable non-controlling interest of approximately $3.1 million and $0.2 million, respectively. The increases in fair value increased the loss attributable to common stockholders. In May 2014, the Company completed the transfer of the open clinical site contracts from Celladon Europe to Celladon and on December 30, 2014, Celladon Europe was dissolved. Upon dissolution, final administrative fees were settled and cash of approximately $0.1 million was transferred from Celladon Europe to Celladon.

Balance Sheet Details

Balance Sheet Details	9 Months Ended	12 Months Ended
	Sep. 30, 2015	Dec. 31, 2014
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Balance Sheet Details	2. Balance Sheet Details Prepaid expenses and other assets consist of the following (in thousands): September 30, December 31, Prepaid clinical expenses (1) $ 388 $ — Prepaid other expenses 546 756 Commercial manufacturing costs (2) — 1,751 Other receivables 67 628 $ 1,001 $ 3,135 (1) During the second half of 2015, following the reduction in workforce initiatives (see Note 7), the Company prepaid certain contract research organizations, or CROs, to manage most aspects of the ongoing CUPID2 trial, including the future payments to clinical sites for patient costs. Additionally, the Company prepaid $0.4 million to CROs in October 2015. (2) The commercial manufacturing costs consisted mainly of design and engineering services for commercial drug manufacturing capabilities. The Company determined that it was probable that it would not complete the commercial manufacturing project in light of the CUPID 2 clinical data announced in April 2015 (see Note 7). The Company therefore recorded the costs accumulated as of December 31, 2014 and activity in 2015 as a period expense in the consolidated financial statements in the nine month period ended September 30, 2015. Property and equipment consist of the following (in thousands): September 30, December 31, Office furniture and other equipment (1) $ 174 $ 881 Leasehold improvements (2) 246 246 Accumulated depreciation (1) (2) (287 ) (364 ) $ 133 $ 763 (1) Following the CUPID 2 trial results and the decision to not pursue additional previously planned development activities with MYDICAR, the Company sold certain MYDICAR manufacturing assets in the third quarter of 2015. The assets had a historical cost of $0.8 million and accumulated depreciation of $0.3 million. The Company had recognized an impairment charge of $0.2 million in the second quarter of 2015 related to the assets which had reduced the net asset value to $0.3 million, the amount of cash proceeds received (see Note 7). (2) In September 2015, in light of the scale-down of certain operations, the Company terminated a sublease agreement effective November 13, 2015, as amended, in order to reduce the Company’s office space and corresponding rent obligations. The sublease was originally scheduled to expire in September 2021. The Company revised the estimated depreciable life of the leasehold improvements associated with the facility to end on November 13, 2015. The change in estimated life resulted in an acceleration of depreciation expense in the amount of $0.1 million in the third quarter of 2015. The net book value of the leasehold improvements was $0.1 million at September 30, 2015. Accounts payable and accrued expenses consist of the following (in thousands): September 30, December 31, Accounts payable $ 228 $ 3,293 Accrued compensation 93 1,909 Accrued other 547 596 Current portion of deferred rent 157 5 $ 1,025 $ 5,803	3. Balance Sheet Details Property and equipment consist of the following (in thousands): As of December 31, 2014 2013 Office furniture and other equipment $ 881 $ 555 Leasehold improvements 246 — Accumulated depreciation (364 ) (247 ) $ 763 $ 308 Accounts payable and accrued expenses consist of the following (in thousands): As of December 31, 2014 2013 Accounts payable $ 3,293 $ 1,397 Accrued compensation 1,909 664 Accrued other 596 839 Current portion of deferred rent 5 8 $ 5,803 $ 2,908

Fair Value Measurements

Fair Value Measurements	9 Months Ended	12 Months Ended
	Sep. 30, 2015	Dec. 31, 2014
Fair Value Disclosures [Abstract]
Fair Value Measurements	3. Fair Value Measurements The Company’s financial instruments primarily consist of cash and cash equivalents, accounts payable and accrued liabilities and historically have included investment securities. The carrying value of these financial instruments generally approximates fair value due to their short-term nature. Investment securities are recorded at fair value. The accounting guidance defines fair value, establishes a consistent framework for measuring fair value and expands disclosure for each major asset and liability category measured at fair value on either a recurring or nonrecurring basis. Fair value is defined as an exit price, representing the amount that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants. As such, fair value is a market-based measurement that should be determined based on assumptions that market participants would use in pricing an asset or liability. As a basis for considering such assumptions, the accounting guidance establishes a three-tier fair value hierarchy, which prioritizes the inputs used in measuring fair value as follows: Level 1: Observable inputs such as quoted prices in active markets; Level 2: Inputs, other than the quoted prices in active markets, that are observable either directly or indirectly; and Level 3: Unobservable inputs in which there is little or no market data, which require the reporting entity to develop its own assumptions As of September 30, 2015 and December 31, 2014, cash and cash equivalents consist primarily of bank deposits with third-party financial institutions and highly liquid money market securities with original maturities at date of purchase of 90 days or less and are stated at cost which approximate fair value and are classified within the Level 1 designation discussed above. Marketable securities are recorded at fair value, defined as the exit price in the principal market in which the Company would transact, representing the amount that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants. Level 2 securities are valued using quoted market prices for similar instruments, non-binding market prices that are corroborated by observable market data, or discounted cash flow techniques and include the Company’s investments in corporate debt securities and commercial paper. Financial liabilities that were measured or disclosed at fair value on a recurring basis, and were classified within the Level 3 designation, included the warrant liability and convertible notes prior to their conversion to equity upon the Company’s initial public offering in February 2014. None of the Company’s non-financial assets and liabilities are recorded at fair value on a non-recurring basis. No transfers between levels have occurred during the periods presented. Cash equivalents measured at fair value as of September 30, 2015 and December 31, 2014 are all classified within Level 1. As of September 30, 2015, the Company had no investment securities. Below is a summary of other assets and liabilities measured at fair value (in thousands): Fair Value Measurements at As of Quoted Prices Significant Significant Assets: Corporate debt securities $ 70,513 $ — $ 70,513 $ —	4. Fair Value Measurements The Company’s financial instruments primarily consist of cash and cash equivalents, investment securities, accounts payable and accrued liabilities. The carrying value of these financial instruments generally approximates fair value due to their short-term nature. Investment securities, warrant liabilities and redeemable non-controlling interest are recorded at fair value. Based on the borrowing rates currently available to the Company for loans with similar terms, which is considered a Level 2 input, the Company believes that the fair value of its convertible debt approximates its carrying value. The accounting guidance defines fair value, establishes a consistent framework for measuring fair value and expands disclosure for each major asset and liability category measured at fair value on either a recurring or nonrecurring basis. Fair value is defined as an exit price, representing the amount that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants. As such, fair value is a market-based measurement that should be determined based on assumptions that market participants would use in pricing an asset or liability. As a basis for considering such assumptions, the accounting guidance establishes a three-tier fair value hierarchy, which prioritizes the inputs used in measuring fair value as follows: Level 1: Observable inputs such as quoted prices in active markets; Level 2: Inputs, other than the quoted prices in active markets, that are observable either directly or indirectly; and Level 3: Unobservable inputs in which there is little or no market data, which require the reporting entity to develop its own assumptions As of December 31, 2014 and 2013, cash and cash equivalents consist primarily of bank deposits with third-party financial institutions and highly liquid money market securities with original maturities at date of purchase of 90 days or less and are stated at cost which approximate fair value and are classified within the Level 1 designation discussed above. Marketable securities are recorded at fair value, defined as the exit price in the principal market in which the Company would transact, representing the amount that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants. Level 2 securities are valued using quoted market prices for similar instruments, non-binding market prices that are corroborated by observable market data, or discounted cash flow techniques and include the Company’s investments in corporate debt securities and commercial paper. Financial assets and liabilities that are measured or disclosed at fair value on a recurring basis, and are classified within the Level 3 designation, include the warrant liability and redeemable non-controlling interest. None of the Company’s non-financial assets and liabilities are recorded at fair value on a non-recurring basis. No transfers between levels have occurred during the periods presented. Cash equivalents measured at fair value as of December 31, 2014 and 2013, are all classified within Level 1. Below is a summary of assets and liabilities measured at fair value (in thousands): Fair Value Measurements at Reporting Date Using As of December 31, 2014 Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Assets: Corporate debt securities $ 70,513 $ — $ 70,513 $ — Fair Value Measurements at Reporting Date Using As of December 31, 2013 Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Assets: Corporate debt securities $ 10,467 $ — $ 10,467 $ — Liabilities: Convertible notes $ 1,044 — — $ 1,044 Warrant liability 1,116 — — 1,116 $ 2,160 $ — $ — $ 2,160 The Company determined the fair value of the convertible notes utilizing an estimated cost of debt for comparable venture backed and mezzanine financings. The fair value per share of the Company’s underlying Series A-1 preferred stock was used to determine the fair value of the redeemable non-controlling interest and the warrant liability. As of February 4, 2014, December 31, 2013, October 15, 2013 (issuance date of Series A-1 warrants), June 6, 2013 (exchange date of exchangeable shares) and December 31, 2012, the fair value of the Series A-1 preferred stock was $0.64, $0.64, $0.91, $0.73 and $0.449, respectively. The fair value of the Series A-1 preferred stock was determined using either an option pricing model, a hybrid option pricing and probability weighted expected return model or, in the case of the February 4, 2014 and December 31, 2013 values, derived from the Company’s IPO price. The key inputs into the models included the probability and timing of expected liquidity event dates, discount rates and the selection of appropriate market comparable transactions and multiples to apply to the Company’s various historical and forecasted operational metrics. In addition to the fair value of the underlying Series A-1 preferred stock, the following assumptions were used in the Black-Scholes option pricing model to determine the fair value of the preferred stock warrant liability: October 15, 2013 December 31, 2013 February 4, 2014 Risk-free interest rate 1.37 % 1.58 % 1.58 % Expected volatility 79 % 82 % 82 % Expected term (in years) 5.0 4.8 4.7 Expected dividend yield 0.0 % 0.0 % 0.0 % The following table provides a reconciliation of all liabilities measured at fair value using Level 3 significant unobservable inputs (in thousands): Redeemable Non-Controlling Interest Convertible Notes Warrant Liability Balance at December 31, 2011 $ — $ — $ — Issuance of shares of redeemable non-controlling interest 4,814 — — Net loss attributable to redeemable non-controlling interest (154 ) — — Change in fair value 154 — — Balance at December 31, 2012 4,814 — — Issuance of warrants in connection with note and warrant purchase agreement — — 954 Issuance of debt — 999 — Net loss attributable to redeemable non-controlling interest (96 ) — — Changes in fair value 3,105 45 162 Exchange of redeemable non-controlling interest for Series A-1 preferred stock (7,823 ) — — Balance at December 31, 2013 — 1,044 1,116 Changes in fair value — 53 183 Reclassification to equity upon initial public offering — — (1,299 ) Conversion to common stock upon initial public offering — (1,097 ) — Balance at December 31, 2014 $ — $ — $ —

Commitments and Contingencies

Commitments and Contingencies	9 Months Ended	12 Months Ended
	Sep. 30, 2015	Dec. 31, 2014
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	4. Commitments and Contingencies Sublicense Agreement and Amended and Restated License Agreement with AmpliPhi Sublicense Agreement In June 2012, the Company entered into a sublicense agreement (the AmpliPhi Sublicense) with AmpliPhi Biosciences Corporation (AmpliPhi), pursuant to which AmpliPhi sublicensed to the Company certain rights under a separate agreement which AmpliPhi entered into in 2009 with the Trustees of University of Pennsylvania (UPenn). Under the terms of the AmpliPhi Sublicense, the Company obtained an exclusive, worldwide sublicense from AmpliPhi under certain UPenn patents related to AAV1 vectors for the development, manufacture, use and sale of companion diagnostics to MYDICAR. In addition, the Company is required to use commercially reasonable efforts to meet certain developmental, regulatory and commercial milestones with respect to companion diagnostics under the agreement. Following the decision to not pursue additional previously planned development activities with MYDICAR and its companion diagnostic, the Company may not currently be in compliance with these milestone requirements and may in the future choose to terminate the agreement. In consideration for the sublicense granted to the Company under the agreement, the Company paid to AmpliPhi a sublicense initiation fee of $310,000, and the Company is obligated to pay to AmpliPhi an annual sublicense maintenance fee of $310,000. The Company is also required to pay to AmpliPhi a low single-digit percentage royalty based on net sales of any companion diagnostic covered by a licensed patent sold by the Company, its affiliates or its sublicensees. The Company’s royalty obligations continue on a companion diagnostic-by-companion diagnostic and country-by-country basis until the expiration of the last-to-expire valid claim in a licensed patent covering the applicable companion diagnostic in such country. Finally, the Company is obligated to pay to AmpliPhi all royalty and milestone payments that become due and payable by AmpliPhi to UPenn under AmpliPhi’s agreement with UPenn as a result of the Company’s exercise of the sublicense granted under the Company’s agreement with AmpliPhi, including a low single-digit tiered percentage royalty on net sales of any companion diagnostic sold by the Company, its affiliates or its sublicensees, which royalty is separate from and in addition to the royalty payable to AmpliPhi described above, and up to an aggregate of $850,000 in potential milestone payments per product covered by the licensed patents. The Company may unilaterally terminate the agreement upon 30 days’ written notice to AmpliPhi. Absent early termination, the agreement will automatically terminate upon the expiration of the last-to-expire licensed patent, which is expected to be in 2019. The Company recorded $0.3 million in research and development expense in each of the nine month periods ended September 30, 2015 and September 30, 2014. Through September 30, 2015, no milestone obligations were incurred under the agreement. Amended and Restated License Agreement The Company entered into an amended and restated license agreement with AmpliPhi concurrently with the AmpliPhi Sublicense that both amended the terms of the license agreement which the Company entered into with AmpliPhi in 2009 and terminated its manufacturing agreement with AmpliPhi which the Company entered into in 2009. Under the agreement, the Company obtained an exclusive, worldwide license under certain patents and know-how related to AmpliPhi’s AAV vector and manufacturing technology for the development, manufacture, use and sale of MYDICAR. In addition, the Company has agreed to use commercially reasonable efforts to meet certain diligence milestones with respect to the development and commercialization of at least one product covered by the UPenn patent rights licensed to AmpliPhi by UPenn under the Company’s agreement with UPenn. Following the decision to not pursue additional previously planned development activities with MYDICAR and its companion diagnostic, the Company may not currently be in compliance with these milestone requirements. During the term of the agreement, the Company is not obligated to make annual license or maintenance payments, but is obligated to pay to AmpliPhi all royalty and milestone payments that become due and payable by AmpliPhi to UPenn under AmpliPhi’s agreement with UPenn as a result of the Company’s exercise of the sublicense granted under the Company’s agreement with AmpliPhi. This includes a low single-digit tiered percentage royalty on net sales of MYDICAR and any other product covered by the licensed patents sold by the Company, its affiliates or its sublicensees, and up to $850,000 in milestone payments upon the achievement of certain developmental and regulatory milestones related to MYDICAR and any other product covered by the licensed patents. Through September 30, 2015, no milestone obligations were incurred under the agreement. The agreement does not provide either party with termination rights and does not have a provision for expiration or automatic termination. Exclusive Patent License with the Regents of the University of Minnesota In May 2009, the Company entered into an exclusive patent license agreement with the Regents of the University of Minnesota (UMinn) under which it obtained an exclusive license to UMinn’s joint ownership interest in a patent application related to screening technology for isolation of small molecule modulators of SERCA enzymes. The agreement did not encompass a manufacturing agreement. The Company suspended further development of the small molecule program in the first half of 2015 and, after review of its strategic alternatives, cancelled the patent license agreement in September 2015. The Company recorded $0.1 million in research and development expense in each of the nine month periods ended September 30, 2015 and September 30, 2014. No milestone obligations were incurred under the agreement. Material Transfer and Exclusivity Agreement In February 2014, the Company and Les Laboratoires Servier (Servier) entered into a material transfer and exclusivity agreement, pursuant to which the Company agreed to transfer to Servier samples of certain proprietary compounds from the Company’s small molecule SERCA2b modulator program and granted to Servier a non-exclusive, non-sublicensable, royalty-free license to conduct certain studies of the samples for the purpose of evaluating Servier’s interest in negotiating a potential license and research collaboration agreement with the Company relating to small molecule SERCA2b modulators (Compounds), for the treatment of type 2 diabetes and other metabolic diseases. In 2015 the Company concluded certain pre-clinical studies in coordination with Servier and the evaluation period has expired. License Agreement with Enterprise On July 18, 2014, the Company and Enterprise Partners Management, LLC (Enterprise), an affiliate of Enterprise Partners Venture Capital, entered into an Assignment and License Agreement (the Enterprise License Agreement), pursuant to which Enterprise granted to the Company an exclusive, worldwide license and the assignment of patents held by Enterprise relating to certain gene therapy applications of the membrane-bound form of the Stem Cell Factor gene (mSCF) for treatment of cardiac ischemia. The Company has the right to grant sublicenses to third parties under the Enterprise License Agreement. Entities affiliated with Enterprise beneficially owned more than 10% of the Company’s stock as of the date the Enterprise License Agreement was executed. In consideration for the rights granted to the Company under the Enterprise License Agreement, the Company paid an upfront fee to Enterprise of $160,000. The Company is also obligated to pay to Enterprise a milestone payment in the amount of $1,000,000 upon the grant to the Company, a Company affiliate or a Company sublicensee of the first regulatory approval in the United States of a product that is covered by the licensed patents. In addition, the Company is required to pay to Enterprise a 2% royalty on net sales of products sold by the Company, Company affiliates and Company sublicensees that are covered by the licensed patents. The Company’s royalty obligations continue on a product-by-product and country-by-country basis until the expiration of the last-to-expire valid claim in the licensed patents covering a licensed product in such country. The Company may unilaterally terminate the Enterprise License Agreement upon written notice to Enterprise. Enterprise may terminate the agreement in the event of the Company’s material breach of the Enterprise License Agreement if such breach remains uncured for 90 days following receipt of written notice of such breach. Absent early termination, the Enterprise License Agreement will automatically terminate upon the expiration of the last-to-expire of the licensed patents containing a valid claim. Other License Agreements The Company has entered into various license agreements pursuant to which the Company acquired certain intellectual property. Pursuant to each agreement the Company paid a license fee and reimbursed historical patent costs. Additionally, under each agreement, the Company may be required to pay annual maintenance fees, royalties, milestone payments and sublicensing fees. Each of the license agreements is generally cancelable by the Company, given appropriate prior written notice. The Company cancelled certain license agreements following the CUPID 2 clinical trial results in April 2015 (see Note 7). Minimum annual payments to maintain these cancelable licenses total an aggregate of approximately $0.1 million and potential future milestone payments total an aggregate of approximately $0.9 million. The Company has recorded research and development expense related to license and annual maintenance fees under the agreements of $0.2 million and $0.2 million for the nine month periods ended September 30, 2015 and September 30, 2014, respectively. Through September 30, 2015, the Company has recorded research and development expense of $0.1 million related to milestone obligations incurred under the agreements. Leases The Company leases office space in San Diego, California under a long-term operating lease that expires in October 2017 and a short-term operating lease that expires in January 2016. In September 2015, in light of the scale-down of certain operations, the Company terminated a sublease agreement for office space effective November 13, 2015, as amended, and paid an early termination fee of approximately $1.0 million. The subleased office space was in San Diego, California and the sublease was originally scheduled to expire in September 2021. In the third quarter of 2015 the Company also terminated its Seattle, Washington leases and paid an early termination fee of $0.2 million. Rent expense for the three months and nine months ended September 30, 2015 was $31,000 and $0.3 million, respectively, which expense included $0.1 million for the acceleration of deferred rent due to the early termination of the sublease agreements. Rent expense for the three months and nine months ended September 30, 2014 was $94,000 and $136,000, respectively. Future minimum payments under the long-term operating leases net of contractual sublease payments total $51,000.	5. Commitments and Contingencies Note and Warrant Purchase Agreement In October 2013, the Company entered into a note and warrant purchase agreement with certain existing investors for the sale of up to an aggregate of $1,097,017 of convertible promissory notes (the 2013 Notes) and warrants exercisable to purchase shares of Series A-1 Preferred Stock (the 2013 Warrants). The terms of the 2013 Notes provided for their automatic conversion (including accrued interest) upon a qualified initial public offering or private placement of equity securities into common stock or other equity securities issued in such private placement at a conversion price per share equal to the initial public offering price or per share purchase price to investors in the private placement. The conversion of the 2013 Notes in the event of a qualified initial public offering or private placement of equity was deemed to be the predominant settlement mechanism. As this predominant settlement mechanism provided for the settlement of a fixed monetary amount in a variable number of equity instruments, the Company concluded that it was appropriate to recognize the 2013 Notes at fair value. The Company valued the 2013 Notes utilizing an estimated cost of debt for comparable venture backed and mezzanine financings. The initial fair value of the 2013 Notes was approximately $1.0 million. Upon completion of the Company’s initial public offering in February 2014, the 2013 Notes plus approximately $20,000 of accrued interest automatically converted into 139,644 shares of common stock. The 2013 Warrants were initially accounted for as liabilities with subsequent changes in fair value recognized within the consolidated statement of operations. The Company determined that the initial fair value of the 2013 Warrants was $1.0 million. The fair value of the 2013 Warrants was derived from the probability weighted expected return model the Company used to value its common stock. Upon completion of the Company’s initial public offering in February 2014, the warrants no longer require liability accounting and the then fair value of the warrant liability was reclassified into equity. The warrants also became exercisable for an aggregate of 231,821 shares of common stock at an exercise price of $5.61 per share. The initial recognition of the 2013 Notes and 2013 Warrants at fair value resulted in a deemed dividend in the amount of $0.9 million that was accounted for as additional net loss attributable to common stockholders. Sublicense Agreement and Amended and Restated License Agreement with AmpliPhi Sublicense Agreement In June 2012, the Company entered into a sublicense agreement (the AmpliPhi Sublicense) with AmpliPhi Biosciences Corporation (AmpliPhi), pursuant to which AmpliPhi sublicensed to the Company certain rights under a separate agreement which AmpliPhi entered into in 2009 with the Trustees of University of Pennsylvania (UPenn). Under the terms of the AmpliPhi Sublicense, the Company obtained an exclusive, worldwide sublicense from AmpliPhi under certain UPenn patents related to AAV1 vectors for the development, manufacture, use and sale of companion diagnostics to MYDICAR. In addition, the Company is required to use commercially reasonable efforts to meet certain developmental, regulatory and commercial milestones with respect to companion diagnostics under the agreement. The Company is currently in compliance with these milestone requirements. In consideration for the sublicense granted to the Company under the agreement, the Company paid to AmpliPhi a sublicense initiation fee of $310,000, and the Company is obligated to pay to AmpliPhi an annual sublicense maintenance fee of $310,000. The Company is also required to pay to AmpliPhi a low single-digit percentage royalty based on net sales of any companion diagnostic covered by a licensed patent sold by the Company, its affiliates or its sublicensees. The Company’s royalty obligations continue on a companion diagnostic-by-companion diagnostic and country-by-country basis until the expiration of the last-to-expire valid claim in a licensed patent covering the applicable companion diagnostic in such country. Finally, the Company is obligated to pay to AmpliPhi all royalty and milestone payments that become due and payable by AmpliPhi to UPenn under AmpliPhi’s agreement with UPenn as a result of the Company’s exercise of the sublicense granted under the Company’s agreement with AmpliPhi, including a low single-digit tiered percentage royalty on net sales of any companion diagnostic sold by the Company, its affiliates or its sublicensees, which royalty is separate from and in addition to the royalty payable to AmpliPhi described above, and up to an aggregate of $850,000 in potential milestone payments per product covered by the licensed patents. The Company may unilaterally terminate the agreement upon 30 days’ written notice to AmpliPhi. Absent early termination, the agreement will automatically terminate upon the expiration of the last-to-expire licensed patent, which is expected to be in 2019. The Company has recorded research and development expense related to sublicense fees under the agreement of $0.3 million, $0.3 million and $0.3 million, respectively, for the years ended December 31, 2014, 2013 and 2012. Through December 31, 2014, no milestone obligations were incurred under the agreement. Amended and Restated License Agreement The Company entered into an amended and restated license agreement with AmpliPhi concurrently with the AmpliPhi Sublicense that both amended the terms of the license agreement which the Company entered into with AmpliPhi in 2009 and terminated its manufacturing agreement with AmpliPhi which the Company entered into in 2009. Under the agreement, the Company obtained an exclusive, worldwide license under certain patents and know-how related to AmpliPhi’s AAV vector and manufacturing technology for the development, manufacture, use and sale of MYDICAR. In addition, the Company has agreed to use commercially reasonable efforts to meet certain diligence milestones with respect to the development and commercialization of at least one product covered by the UPenn patent rights licensed to AmpliPhi by UPenn under the Company’s agreement with UPenn. The Company is currently in compliance with these milestone requirements. During the term of the agreement, the Company is not obligated to make annual license or maintenance payments, but is obligated to pay to AmpliPhi all royalty and milestone payments that become due and payable by AmpliPhi to UPenn under AmpliPhi’s agreement with UPenn as a result of the Company’s exercise of the sublicense granted under the Company’s agreement with AmpliPhi. This includes a low single-digit tiered percentage royalty on net sales of MYDICAR and any other product covered by the licensed patents sold by the Company, its affiliates or its sublicensees, and up to $850,000 in milestone payments upon the achievement of certain developmental and regulatory milestones related to MYDICAR and any other product covered by the licensed patents. Through December 31, 2014, no milestone obligations were incurred under the agreement. The agreement does not provide either party with termination rights and does not have a provision for expiration or automatic termination. In addition, the Company paid $3.2 million in exchange for certain intangible assets associated with the license agreement that the Company acquired from AmpliPhi in June 2012, which were expensed as in-process research and development during the year ended December 31, 2012. Exclusive Patent License with the Regents of the University of Minnesota In May 2009, the Company entered into an exclusive patent license agreement with the Regents of the University of Minnesota (UMinn) under which it obtained an exclusive license to UMinn’s joint ownership interest in a patent application related to screening technology for isolation of small molecule modulators of SERCA enzymes. The agreement does not encompass a manufacturing agreement. The Company has agreed to meet certain performance milestones under the agreement, the deadline for which may be extended at the Company’s request provided that the Company has used commercially reasonable efforts to achieve such milestones by the applicable deadlines. The Company is currently in compliance with these milestone requirements. The Company has the first right to prosecute and maintain the applicable patent family. The Company made an upfront payment to UMinn of $120,000. In addition, the Company is obligated to pay to UMinn an annual license fee of $120,000. The annual license fee will increase to $325,000 if the Company (1) undergoes a change of control, (2) assigns the agreement, any of its rights or obligations under the agreement or as joint ownership interest in the licensed technology, (3) receives a certain amount in license and sublicense revenues under the agreement, (4) files an investigational new drug application, or IND, new drug application, biologic license application or orphan drug application (or a foreign equivalent of any such application) for a product covered by the licensed technology, or (5) enters into any agreement with a third party to market or use the licensed technology, subject to certain exceptions. The Company may unilaterally terminate the agreement upon 90 days’ written notice to UMinn. UMinn may terminate the agreement upon 10 days’ written notice to the Company upon the Company’s insolvency or for its breach of the agreement if such breach remains uncured for 90 days after the Company receives notice of such breach, or 30 days in the case of a non-payment breach. Absent early termination, the agreement will automatically terminate upon the expiration of all active claims in any licensed patent or patent application, which is expected to occur no earlier than January 2030. The Company has recorded research and development expense related to license and annual maintenance fees under the agreement of $0.1 million, $0.1 million, and $0.1 million, respectively, for the years ended December 31, 2014, 2013 and 2012. Through December 31, 2014, no milestone obligations were incurred under the agreement. Material Transfer and Exclusivity Agreement In February 2014, the Company and Les Laboratoires Servier (Servier) entered into a material transfer and exclusivity agreement, pursuant to which the Company agreed to transfer to Servier samples of certain proprietary compounds from the Company’s small molecule SERCA2b modulator program and granted to Servier a non-exclusive, non-sublicensable, royalty-free license to conduct certain studies of the samples for the purpose of evaluating Servier’s interest in negotiating a potential license and research collaboration agreement with the Company relating to small molecule SERCA2b modulators (Compounds), for the treatment of type 2 diabetes and other metabolic diseases. Although the evaluation period under this Agreement has expired, the Company is in the process of completing certain pre-clinical studies of these compounds in coordination with Servier and Servier is continuing to evaluate its potential interest in this program. Under the terms of the agreement, the Company also granted to Servier the exclusive right to negotiate for an exclusive, royalty-bearing license to develop and commercialize Compounds, and products containing Compounds, in the field of type 2 diabetes and other metabolic diseases, or the field, solely outside of the United States and its territories and possessions on the terms and conditions set forth in the agreement and other commercially reasonable terms to be negotiated in good faith by the parties and set forth in a definitive license and research collaboration agreement. License Agreement with Enterprise On July 18, 2014, the Company and Enterprise Partners Management, LLC (Enterprise), an affiliate of Enterprise Partners Venture Capital, entered into an Assignment and License Agreement (the Enterprise License Agreement), pursuant to which Enterprise granted to the Company an exclusive, worldwide license and the assignment of patents held by Enterprise relating to certain gene therapy applications of the membrane-bound form of the Stem Cell Factor gene (mSCF) for treatment of cardiac ischemia. The Company has the right to grant sublicenses to third parties under the Enterprise License Agreement. Entities affiliated with Enterprise beneficially owned more than 10% of Celladon’s stock as of the date the Enterprise License Agreement was executed. In consideration for the rights granted to the Company under the Enterprise License Agreement, the Company paid an upfront fee to Enterprise of $160,000. The Company is also obligated to pay to Enterprise a milestone payment in the amount of $1,000,000 upon the grant to the Company, a Company affiliate or a Company sublicensee of the first regulatory approval in the United States of a product that is covered by the licensed patents. In addition, the Company is required to pay to Enterprise a 2% royalty on net sales of products sold by the Company, Company affiliates and Company sublicensees that are covered by the licensed patents. The Company’s royalty obligations continue on a product-by-product and country-by-country basis until the expiration of the last-to-expire valid claim in the licensed patents covering a licensed product in such country. The Company may unilaterally terminate the Enterprise License Agreement upon written notice to Enterprise. Enterprise may terminate the agreement in the event of the Company’s material breach of the Enterprise License Agreement if such breach remains uncured for 90 days following receipt of written notice of such breach. Absent early termination, the Enterprise License Agreement will automatically terminate upon the expiration of the last-to-expire of the licensed patents containing a valid claim. Other License Agreements The Company has entered into various license agreements pursuant to which the Company acquired certain intellectual property. Pursuant to each agreement the Company paid a license fee and reimbursed historical patent costs. Additionally, under each agreement, the Company may be required to pay annual maintenance fees, royalties, milestone payments and sublicensing fees. Each of the license agreements is generally cancelable by the Company, given appropriate prior written notice. Minimum annual payments to maintain these cancelable licenses total an aggregate of approximately $0.2 million and potential future milestone payments total an aggregate of approximately $3.3 million. The Company has recorded research and development expense related to license and annual maintenance fees under the agreements of $0.2 million for each of the years ended December 31, 2014, 2013 and 2012. Through December 31, 2014, the Company has recorded research and development expense of $0.1 million related to milestone obligations incurred under the agreements. Leases The Company leases office space in San Diego, California under long-term operating leases that expire in October 2017 and September 2021. On July 1, 2014, the Company relocated its San Diego office to another location in San Diego and is subleasing the prior space. The Company also has short-term leases for satellite office space in Seattle, Washington and housing accommodation in San Diego that expire in 2015. Rent expense was $0.3 million, $0.1 million and $0.1 million for the years ended December 31, 2014, 2013 and 2012, respectively. In March 2015, the Company entered into a short-term lease for approximately 7,000 additional square feet of office space in Seattle, Washington that expires in June 2016. The future minimum annual rental commitments under the lease obligations and sublease rental receipts at December 31, 2014 are as follows (in thousands): Lease Obligations Sublease Rental Receipts Total Year ending December 31: 2015 $ 466 $ (75 ) $ 391 2016 487 (77 ) 410 2017 485 (67 ) 418 2018 414 — 414 2019 426 — 426 Thereafter 776 — 776 Total $ 3,054 $ (219 ) $ 2,835

Long-Term Obligations

Long-Term Obligations	9 Months Ended	12 Months Ended
	Sep. 30, 2015	Dec. 31, 2014
Debt Disclosure [Abstract]
Long-Term Obligations	6. Long-Term Obligations Hercules Loan Agreement On July 31, 2014, the Company entered into a Loan and Security Agreement (the Loan Agreement) with Hercules Technology III, L.P. and Hercules Technology Growth Capital, Inc. (as agent and as a lender, and together with Hercules Technology III, L.P., the Lenders) under which up to $25.0 million was available for the Company to borrow in two tranches (the Loan). The Company borrowed the first tranche of $10.0 million on August 1, 2014. The Loan accrued interest at a rate equal to the greater of either (i) 8.25% plus the prime rate as reported from time to time in The Wall Street Journal minus 5.25%, and (ii) 8.25%. Contractual payments under the Loan Agreement were interest only until August 1, 2015 followed by equal monthly payments of principal and interest, through the scheduled maturity date on February 1, 2018. In addition, a final payment equal to $1,750,000 was due at such time as the Loan was prepaid or became due and payable in full as specified in the Loan Agreement. The second tranche of up to $15.0 million was available to be drawn through June 30, 2015, but only if the Company provided the Lenders with notice that data from the Company’s Phase 2b clinical trial for MYDICAR supported the continued development of MYDICAR for its Breakthrough Therapy designation to either a Phase 3 clinical trial or for registration for approval, as reasonably determined by the Company’s senior management and board of directors (the Milestone). In April 2015, the Company’s senior management and board of directors determined that the Company did not achieve the Milestone (see Note 7). Accordingly, the Company could not draw down the second tranche of $15.0 million. In June 2015 the Company announced it would prepay the outstanding amounts due under the Loan Agreement and on August 3, 2015, the Company paid the Lenders (i) the $10,000,000 outstanding principal balance, (ii) $75,625 in accrued and unpaid interest, and (iii) an end of term charge of $1,750,000, for a total payment of $11,825,625. Upon the prepayment on August 3, 2015, the Company’s obligations, covenants, debts and liabilities under the Loan Agreement were satisfied in full and the Lender’s commitments to extend further credit to the Company were terminated. Capital Lease In 2014 the Company entered into a capital lease arrangement for office equipment in the Company’s San Diego, California office. The Company was obligated to make 60 payments of approximately $600. In September 2015 the Company purchased and obtained title to the office equipment. At September 30, 2015, the Company had no capital lease obligations.	6. Long-Term Obligations Hercules Loan Agreement On July 31, 2014, the Company entered into a Loan and Security Agreement (the Loan Agreement) with Hercules Technology III, L.P. and Hercules Technology Growth Capital, Inc. (as agent and as a lender, and together with Hercules Technology III, L.P., the Lenders) under which the Company may borrow up to $25.0 million in two tranches (the Loan). The Company borrowed the first tranche of $10.0 million on August 1, 2014 and paid a facility charge to the Lenders of $150,000 in addition to $37,500 previously paid to the Lenders as a commitment fee. The Company plans to use the proceeds of the Loan to provide additional funding for the development of MYDICAR, for other development programs in its pipeline and for general corporate purposes. The second tranche of up to $15.0 million can be drawn through June 30, 2015 (amended from May 31, 2015), but only if the Company has provided the Lenders with notice that data from the Company’s Phase 2b clinical trial for MYDICAR supports the continued development of MYDICAR for its Breakthrough Therapy designation to either a Phase 3 clinical trial or for registration for approval, as reasonably determined by the Company’s senior management and board of directors (the Milestone). Upon funding of the second tranche of the Loan, the Company will be required to pay a facility charge to the Lenders of $100,000. The interest rate for each tranche will be calculated at a rate equal to the greater of either (i) 8.25% plus the prime rate as reported from time to time in The Wall Street Journal minus 5.25%, and (ii) 8.25%. Payments under the Loan Agreement are interest only until August 1, 2015 (which will be extended until February 1, 2016 if the Company achieves the Milestone on or before June 30, 2015) (the Amortization Date) followed by equal monthly payments of principal and interest through the scheduled maturity date on February 1, 2018 (the Loan Maturity Date). In addition, a final payment equal to $1,750,000 will be due at such time as the Loan is prepaid or becomes due and payable as specified in the Loan Agreement. The Company’s obligations under the Loan Agreement are secured by a security interest in substantially all of its assets, excluding its intellectual property but including the proceeds from the sale, licensing or disposition of its intellectual property. The Company’s intellectual property is also subject to customary negative covenants. If the Company prepays the loan prior to maturity, it will pay the Lenders a prepayment charge, based on a percentage of the then outstanding principal balance, equal to 1.5% if the prepayment occurs prior to the Amortization Date. Subject to certain conditions and limitations set forth in the Loan Agreement, including ownership limitations of the Lenders, the Company has the right to convert up to $3.0 million of scheduled principal installments of the Loan into shares of the Company’s common stock, provided such shares must be freely tradable. The number of shares of common stock that would be issued upon conversion would be equal to the number determined by dividing (x) the principal amount to be paid in shares of common stock by (y) $16.33. The Loan Agreement includes customary representations, warranties and covenants (affirmative and negative) of the Company, including restrictive covenants that limit the Company’s ability to: incur additional indebtedness; encumber the collateral securing the Loan; acquire, own or make investments; repurchase or redeem stock or other equity securities; declare or pay any cash dividend or make a cash distribution on any class of stock or other equity interest; transfer a material portion of the Company’s assets; acquire other businesses; and merge or consolidate with or into any other business organization. The Loan Agreement does not however include any financial maintenance covenants. The Loan Agreement also includes standard events of default, including payment defaults, breaches of covenants following any applicable cure period, a material impairment in the perfection or priority of the Lenders’ security interest or in the value of the collateral, and events relating to bankruptcy or insolvency. Upon the occurrence of an event of default, a default interest rate of an additional 5% may be applied to the outstanding Loan, and the Lenders may declare all outstanding obligations immediately due and payable and take such other actions as are set forth in the Loan Agreement. Capital Lease In 2014 the Company entered into a capital lease arrangement for office equipment in the Company’s San Diego, California office. Contractual Payments and Carrying-Value Reconciliation As of December 31, 2014, future contractual principal and final fee payments on the Company’s debt and capital lease obligations are as follows (in thousands): Year ending December 31: Total Term Loan Capital Lease 2015 $ 1 $ — $ 1 2016 3,432 3,430 2 2017 4,052 4,049 3 2018 4,275 4,271 4 2019 2 — 2 Total $ 11,762 $ 11,750 $ 12 The following table provides a reconciliation of the Company’s future contractual principal and final fee payments on its debt and capital lease obligations to the reported carrying value as of December 31, 2014 (in thousands): Total loan debt and capital lease obligations $ 11,762 Less: Debt discount (1,659 ) Total carrying value: 10,103 Less: Carrying value of current portion of long-term obligations (1 ) Carrying value of long-term obligations, less current portion 10,102 Interest expense for the years ended December 31, 2014, 2013 and 2012 was $0.7 million, $0.1 million and $0.1 million, respectively. Interest expense in 2014 related mainly to the Hercules Loan Agreement and interest expense in prior years related mainly to convertible debt outstanding in those periods.

Preferred Stock and Stockholder

Preferred Stock and Stockholders' Equity (Deficit)	9 Months Ended	12 Months Ended
	Sep. 30, 2015	Dec. 31, 2014
Equity [Abstract]
Preferred Stock and Stockholders' Equity (Deficit)	5. Stockholders’ Equity Common Stock Warrants The following table summarizes the fully exercisable warrants outstanding for the purchase of common stock as of September 30, 2015 and December 31, 2014: September 30, 2015 December 31, 2014 Exercise Price Expiration Date 152,735 206,340 $ 5.61 October 2018 Stock Options Options granted under the Company’s equity incentive plans generally expire no more than ten years from the date of grant and generally vest and become exercisable over a period not to exceed four years, as determined by the Company’s board of directors. Recipients of stock options are eligible to purchase shares of the Company’s common stock at an exercise price equal to no less than the estimated fair market value of such stock on the date of grant. The Company has also granted inducement stock options outside an equity incentive plan that are subject to the terms and conditions of the Company’s 2013 Equity Incentive Plan. Prior Plans In December 2001, the Company adopted its 2001 Stock Option Plan (the 2001 Plan) and in January 2012 adopted its 2012 Equity Incentive Plan (the 2012 Plan, and together with the 2001 Plan, the Prior Plans). The Prior Plans have terminated and no further shares may be granted under the Prior Plans. 2013 Equity Incentive Plan The 2013 Equity Incentive Plan became effective in February 2014. Under the 2013 Equity Incentive Plan, the Company may grant stock options, stock appreciation rights, restricted stock, restricted stock units (RSUs), performance-based stock awards and other awards to individuals who are then employees, officers, non-employee directors or consultants of the Company and its affiliates. Additionally, the 2013 Equity Incentive Plan provides for the grant of performance cash awards. The number of shares of common stock reserved for issuance under the 2013 Equity Incentive Plan will automatically increase on January 1 of each year continuing through and including January 1, 2023 by 5% of the total number of shares of the Company’s capital stock outstanding on December 31 of the preceding calendar year, or a lesser number of shares determined by the Company’s board of directors. A summary of the Company’s stock option and RSU activity is as follows: Options and RSUs Outstanding at December 31, 2014 2,408,634 Granted 1,342,750 Exercised (383,011 ) Cancelled (1,841,275 ) Outstanding at September 30, 2015 1,527,098 2013 Employee Stock Purchase Plan The 2013 Equity Stock Purchase Plan (ESPP) became effective in January 2014. The number of shares of common stock reserved for issuance will automatically increase on January 1 of each calendar year through January 1, 2023 by the least of (1) 1% of the total number of shares of the Company’s common stock outstanding on December 31 of the preceding calendar year, (2) 384,307 shares, or (3) a number determined by the Company’s board of directors that is less than (1) and (2). Stock-Based Compensation Expense The allocation of stock-based compensation for all equity awards is as follows (in thousands): Three Months Nine Months 2015 2014 2015 2014 Research and development (1) $ (663 ) $ 391 $ 929 $ 1,175 General and administrative 645 520 2,254 1,003 $ (18 ) $ 911 $ 3,183 $ 2,178 (1) During the three months ended September 30, 2015, following the reduction in workforce initiatives (see Note 7), the Company reversed the previously recorded expense for unvested options of terminated employees aggregating $0.8 million. As of September 30, 2015 the unrecognized compensation cost related to outstanding employee options was $7.3 million and is expected to be recognized as expense over approximately 2.9 years.	7. Preferred Stock and Stockholders’ Equity (Deficit) Preferred Stock In addition to its redeemable convertible preferred stock, the Company’s convertible preferred stock has been classified as temporary equity at December 31, 2013 on the accompanying consolidated balance sheets instead of in stockholders’ deficit in accordance with authoritative guidance for the classification and measurement of potentially redeemable securities whose redemption is based upon certain change in control events that are outside of the control of the Company, including liquidation, sale or transfer of control of the Company. On February 4, 2014, in connection with the Company’s initial public offering, all outstanding shares of convertible preferred stock were converted into 11,151,192 shares of the Company’s common stock. The authorized, issued and outstanding shares of preferred stock by series are as follows (in thousands, except share amounts): Shares Authorized Shares Outstanding Liquidation Preference Redemption Amount As of December 31, 2014 Preferred stock 10,000,000 — — — As of December 31, 2013 Redeemable convertible preferred stock: Series A-1 135,826,497 127,140,530 $ 114,172 $ 57,086 Convertible preferred stock: Junior preferred stock 12,138,080 12,138,080 5,450 — Total 147,964,577 139,278,610 $ 119,622 $ 57,086 Common Stock and Common Stock Warrants In February 2014, the Company completed its initial public offering in which it sold 6,325,000 shares of common stock at a public offering price of $8.00 per share. The proceeds received and costs incurred in connection with the Company’s initial public offering, shown in the period received or paid, were as follows (in thousands): Year ended December 31, Total 2014 2013 Gross proceeds (including over-allotment) $ 50,600 $ 50,600 $ — Underwriting discounts and commissions (3,542 ) (3,542 ) — Offering costs (2,800 ) (1,107 ) (1,693 ) Net proceeds $ 44,258 $ 45,951 $ (1,693 ) In addition, each of the following occurred on February 4, 2014 in connection with the Company’s initial public offering: • Series A-1 redeemable convertible preferred stock outstanding (127,140,530 shares) and Junior preferred convertible stock outstanding (12,138,080 shares) were converted into 10,179,372 and 971,820 shares of the Company’s common stock, respectively; • the outstanding principal balance of $1,097,017 and accrued interest of $20,000 on convertible promissory notes converted into 139,644 shares of the Company’s common stock; • warrants to purchase 2,895,570 shares of Series A-1 preferred stock were converted into warrants to purchase 231,821 shares of the Company’s common stock and the warrant liability was reclassified to additional paid-in capital. In August 2014, the Company completed an underwritten public offering in which it sold 4,600,000 shares of common stock at a public offering price of $9.50 per share. The proceeds received and costs incurred in connection with this offering, shown in the period received or paid, were as follows (in thousands): 2014 Gross proceeds (including option to purchase additional shares) $ 43,700 Underwriting discounts and commissions (2,622 ) Offering costs (389 ) Net proceeds $ 40,689 The following table summarizes the fully exercisable warrants outstanding for the purchase of common stock as of December 31, 2014 and 2013: December 31, Exercise Expiration 2014 2013 Price Date — 80 $ 224.82 January 2015 — 622 $ 12.49 October 2016 206,340 — $ 5.61 October 2018 206,340 702 Stock Options Options granted under the Company’s equity incentive plans generally expire no more than 10 years from the date of grant and generally vest and become exercisable over a period not to exceed four years, as determined by the Company’s board of directors. Recipients of stock options are eligible to purchase shares of the Company’s common stock at an exercise price equal to no less than the estimated fair market value of such stock on the date of grant. Prior Plans In December 2001, the Company adopted its 2001 Stock Option Plan (the 2001 Plan) and in January 2012 adopted its 2012 Equity Incentive Plan (the 2012 Plan, and together with the 2001 Plan, the Prior Plans). The Prior Plans have terminated and no further shares may be granted under the Prior Plans. 2013 Equity Incentive Plan In October 2013, the Company’s stockholders approved the 2013 Equity Incentive Plan, as amended (2013 Plan), which became effective in February 2014. Under the 2013 Plan, the Company may grant stock options, stock appreciation rights, restricted stock, restricted stock units, performance-based stock awards and other awards to individuals who are then employees, officers, non-employee directors or consultants of the Company and its affiliates. Additionally, the 2013 Plan provides for the grant of performance cash awards. Initially, the aggregate number of shares of common stock that may be issued pursuant to stock awards under the 2013 Plan is the sum of (1) 1,473,738 shares, plus (2) the number of shares (not to exceed 1,569,905 shares) (i) the 26,294 shares reserved for issuance under the 2012 Plan at the time the 2013 Plan became effective, and (ii) any shares subject to outstanding stock options or other stock awards that were granted under the 2012 Plan or 2001 Plan that are forfeited, terminate, expire or are otherwise not issued. Additionally, the number of shares of common stock reserved for issuance under the 2013 Plan will automatically increase on January 1 of each year, beginning on January 1, 2015 and continuing through and including January 1, 2023, by 5% of the total number of shares of the Company’s capital stock outstanding on December 31 of the preceding calendar year, or a lesser number of shares determined by the Company’s board of directors. A summary of the Company’s stock option activity under the Prior Plans and 2013 Plan is as follows: Options Weighted- Average Exercise Price Per Share Weighted- Average Remaining Contractual Term Aggregate Intrinsic Value (in 000’s) Outstanding at December 31, 2013 1,543,667 $ 3.19 8.66 $ 9,128 Granted 1,240,673 10.61 Exercised (340,220 ) 1.20 Canceled (35,486 ) 10.93 Outstanding at December 31, 2014 2,408,634 $ 7.18 8.53 $ 31,031 Options exercisable at December 31, 2014 1,263,695 $ 4.02 7.78 $ 20,877 Options exercisable, vested and expected to vest at December 31, 2014 2,408,634 $ 7.18 8.53 $ 31,031 The weighted-average grant date fair value of employee options granted during the years ended December 31, 2014, 2013 and 2012 was $7.36, $7.27 and $0.75 per share, respectively. The aggregate intrinsic value of options exercised during the year ended December 31, 2014 was approximately $3.9 million. There were no options exercised in the years prior to the Company’s initial public offering in 2014. 2013 Employee Stock Purchase Plan In October 2013, the Company’s stockholders approved the 2013 Equity Stock Purchase Plan (ESPP) which became effective in February 2014. Initially, the ESPP authorizes the issuance of 165,732 shares of common stock pursuant to purchase rights granted to the Company’s employees or to employees of any of the Company’s designated affiliates. The number of shares of common stock reserved for issuance will automatically increase on January 1 of each calendar year, from January 1, 2015 through January 1, 2023 by the least of (1) 1% of the total number of shares of the Company’s common stock outstanding on December 31 of the preceding calendar year, (2) 384,307 shares, or (3) a number determined by the Company’s board of directors that is less than (1) and (2). During the year ended December 31, 2014, the Company recorded stock-based compensation expense of approximately $0.1 million related to the ESPP. Stock-Based Compensation Expense The weighted-average assumptions used in the Black-Scholes option pricing model to determine the fair value of the employee stock option grants were as follows: As of December 31, 2014 2013 2012 Risk-free interest rate 1.90 % 1.62 % 2.29 % Expected volatility 80 % 79 % 84 % Expected term (in years) 6.0 5.6 5.9 Expected dividend yield 0.0 % 0.0 % 0.0 % Risk-free interest rate. Expected volatility. Expected term. Expected dividend yield. The allocation of stock-based compensation for all equity awards is as follows (in thousands): As of December 31, 2014 2013 2012 Research and development $ 1,712 $ 1,264 $ 222 General and administrative 1,607 124 76 $ 3,319 $ 1,388 $ 298 As of December 31, 2014 the unrecognized compensation cost related to outstanding employee options was $8.9 million and is expected to be recognized as expense over approximately 3.0 years. Common Stock Reserved for Future Issuance Common stock reserved for future issuance as of December 31, 2014 and 2013 is as follows: December 31, 2014 2013 Granted and outstanding under the Plans 2,408,634 1,543,667 Available for grant under the 2012 Plan 294,845 26,294 Available for issuance under Employee Stock Purchase Plan 140,711 — Common stock warrants issued and outstanding 206,340 702 Convertible preferred stock warrants issued and outstanding — 231,821 Convertible preferred stock — 11,151,192 3,050,530 12,953,676

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2014
Income Tax Disclosure [Abstract]
Income Taxes	8. Income Taxes The following is a reconciliation of the expected statutory federal income tax provision to the actual income tax provision (in thousands): December 31, 2014 2013 2012 Tax computed at federal statutory rate $ (11,510 ) $ (6,831 ) $ (5,396 ) State income tax, net of federal benefit (1,517 ) (987 ) (907 ) Non-deductible interest 20 20 36 Other permanent items 1,676 756 214 Research credits (557 ) (728 ) (93 ) Remove (restore) DTA for NOL and Credits – IRC 382 — (12,666 ) 2,135 State Taxes — — — Uncertain tax position (1,125 ) 859 — Valuation allowance 13,013 19,577 4,011 Provision (benefit) for income taxes $ — $ — $ — The components of the Company’s deferred tax assets are summarized as follows (in thousands): December 31, 2014 2013 Deferred tax assets: Net operating loss carryforwards $ 31,484 $ 19,288 Research credits 1,649 1,092 Capitalized R&D 5,410 6,391 Other 2,049 803 Deferred tax assets 40,592 27,574 Valuation allowance (40,592 ) (27,574 ) Net deferred tax assets $ — $ — The Company has established a valuation allowance for all deferred tax assets (DTA) including those for new operating loss and tax credit carryforwards. A valuation allowance of approximately $40.6 million of which approximately $13.0 million relates to 2014, has been recognized to offset the deferred tax assets, as realization of such assets is uncertain. At December 31, 2014, the Company had federal and California net operating loss (NOL) carryforwards of approximately $82.2 million and $77.0 million, respectively. The federal NOL carryforwards will begin to expire in 2027 unless previously utilized, and the state NOL carryforwards have already begun to expire, and will continue to do so, unless utilized. At December 31, 2014, the Company had federal and state research tax credits each of $1.3 million. The federal research tax credits begin to expire in 2032 unless previously utilized. The California research credit will carry forward indefinitely until utilized. Utilization of the NOL and research tax credit carryforwards may be subject to a substantial annual limitation due to ownership change limitations that have occurred or that could occur in the future, as required by Section 382 of the Code, as well as similar state and foreign provisions. These ownership changes may limit the amount of NOL and research tax credit carryforwards that can be utilized annually to offset future taxable income and tax, respectively. In general, an “ownership change” as defined by Section 382 of the Code results from a transaction or series of transactions over a three-year period resulting in an ownership change of more than 50 percentage points of the outstanding stock of a company by certain stockholders or public groups. The Company completed a study to assess whether an ownership change, as defined by Section 382 of the Code, had occurred from the Company’s formation through December 31, 2014. Based upon this study, the Company determined that several ownership changes had occurred. Accordingly, the Company has reduced its deferred tax assets related to the federal and state NOL carryforwards and the federal research tax credit carryforwards that are anticipated to expire unused as a result of these ownership changes. These tax attributes have been excluded from the deferred tax assets with a corresponding reduction in the valuation allowance with no net effect on income tax expense or the effective tax rate. Future ownership changes may further limit the Company’s ability to utilize its remaining tax attributes. The Company adopted the provisions of Financial Accounting Standards Board (FASB) ASC 740-10 Income Taxes The following table summarized the activity related to the Company’s unrecognized tax benefits (in thousands): Year Ended December 31, 2014 2013 Balance beginning of the year $ 1,709 $ — Increase related to prior year tax positions (1,361 ) 681 Increase related to current year tax positions 314 1,028 Balance at end of year $ 662 $ 1,709 There were no unrecognized tax benefits prior to 2013. Approximately $0.7 million of the unrecognized tax benefits would reduce the Company’s annual effective tax rate, if recognized, subject to the valuation allowance. It is not anticipated that there will be significant change in the unrecognized tax benefits over the next 12 months. Due to the net operating loss carryforwards, the U.S. federal and state returns are open to examination by the Internal Revenue Service and significant state and foreign jurisdictions for all years beginning with the inception of the Company. The Company’s policy is to recognize interest expense and penalties related to income tax matters as a component of income tax expense. There was no interest and penalties associated with uncertain tax positions as of December 31, 2014.

Employee Benefits

Employee Benefits	12 Months Ended
	Dec. 31, 2014
Postemployment Benefits [Abstract]
Employee Benefits	9. Employee Benefits All employees of the Company are eligible to participate in the 401(k) Plan. The 401(k) matching contributions, if any, are determined by the Company at its sole discretion. During the years ended December 31, 2014, 2013 and 2012, the Company made matching contributions totaling $0.3 million, $0.1 million, $0.1 million, respectively.

Subsequent Events

Subsequent Events	12 Months Ended
	Dec. 31, 2014
Subsequent Events [Abstract]
Subsequent Events	10. Subsequent Events Novasep Agreement On March 20, 2015, the Company entered into a Development, Manufacturing and Supply Agreement (the “Manufacturing Agreement”) with Novasep, Inc. (“Novasep”) which superseded the Letter Agreement dated December 19, 2014 by and between the Company and Novasep. Under the terms of the Manufacturing Agreement, the parties agreed to continue the work initiated under the Letter Agreement, including the work necessary to prepare for the potential manufacture of MYDICAR drug substance (AAV1/SERCA2a) at the facilities of Novasep’s affiliate Henogen in Europe (the “Novasep Facility”). Pursuant to the Manufacturing Agreement (and as previously agreed in the Letter Agreement), in exchange for payments from the Company to Novasep totaling up to €4,750,000, Novasep agreed to (i) conduct the engineering design work for facility modifications that would be necessary for the manufacture of MYDICAR drug substance, (ii) undertake initial process and analytical transfer and initial scale-up work in support of such potential future commercial manufacturing of MYDICAR drug substance, and (iii) allocate the resources and capacity necessary for the foregoing activities. The parties have also agreed to proceed with the additional process transfer, engineering/construction, scale-up and development activities necessary for future production of MYDICAR drug substance in accordance with current Good Manufacturing Practices (“GMP”), and agreed to terms of a commercial supply arrangement with a term through at least December 31, 2018, with extension options through 2020 in favor of the Company. The Company has the right to terminate the Manufacturing Agreement, exercisable for a specified period of time following the un-blinding of the data from the Company’s Phase 2b clinical trial of MYDICAR (CUPID 2), if the Company concludes in good faith that the CUPID 2 data is such that the Company does not require production of MYDICAR drug substance at the Novasep Facility. The Company expects to un-blind the data from the CUPID 2 trial in late April 2015. Unless the Company exercises the post CUPID 2 data termination right described above, the Company will be obligated to (i) fund Novasep’s modifications to the Novasep Facility through time- and event-triggered milestone payments, (ii) make additional payments for the development services to be performed by Novasep, and (iii) commit to purchase a specified number of batches of MYDICAR drug substance (or make minimum payments with respect to any such batches that are not purchased) through 2018 (if the Company elects that the Novasep Facility be operated as a multi-product facility) or through 2019 (if the Company elects to have the Novasep Facility dedicated to MYDICAR drug substance production during the term of the Manufacturing Agreement). In addition to the above-described post CUPID 2 data termination right, the Company has the right to terminate the Manufacturing Agreement (i) at will on or before March 31, 2016, (ii) following the shut-down or non-production of the Novasep Facility for a specified period of time, or (iii) upon Novasep’s debarment. Additionally, each party may terminate the Manufacturing Agreement upon uncured material breach thereof by the other party, upon the other party’s insolvency or bankruptcy, or in the event of a continuing force majeure preventing performance. Upon any termination of the Manufacturing Agreement by Celladon following the expiration of the post CUPID 2 data termination right either for convenience or for any reason other than material breach of the Manufacturing Agreement, shut-down or non-production of the Novasep Facility for a period extending longer than six months, or Novasep’s insolvency, the Company is obligated to pay previously-unreimbursed amounts incurred by Novasep and specified termination fees as set forth in the Manufacturing Agreement.

Selected Quarterly Financial Da

Selected Quarterly Financial Data	12 Months Ended
	Dec. 31, 2014
Quarterly Financial Information Disclosure [Abstract]
Selected Quarterly Financial Data	11. Selected Quarterly Financial Data (Unaudited) The following financial information reflects all normal recurring adjustments, which are, in the opinion of management, necessary for a fair statement of the results of the interim periods. Summarized quarterly data for fiscal 2014 and 2013 are as follows (in thousands, except per share data): First Quarter Second Quarter Third Quarter Fourth Quarter 2014 Total operating expenses $ 6,924 $ 7,005 $ 8,131 $ 10,958 Consolidated Net loss (7,162 ) (6,992 ) (8,358 ) (11,341 ) Basic and diluted net loss per share $ (0.60 ) $ (0.38 ) $ (0.40 ) $ (0.49 ) 2013 Total operating expenses $ 3,472 $ 4,992 $ 5,523 $ 5,977 Consolidated Net loss (3,530 ) (4,929 ) (5,453 ) (6,179 ) Basic and diluted net loss per share $ (3.99 ) $ (8.98 ) $ (6.17 ) $ (7.96 )

Restructuring charges

Restructuring charges	9 Months Ended
	Sep. 30, 2015
Restructuring and Related Activities [Abstract]
Restructuring charges	7. Restructuring charges On April 26, 2015, the Company announced that its Phase 2b CUPID 2 trial did not meet its primary and secondary endpoints. No safety issues were noted. In light of the CUPID 2 results and following analysis of the CUPID 2 data, the Company’s board of directors, in two phases prior to September 30, 2015, approved an approximately 70% aggregate reduction of the Company’s peak workforce of 34 employees to reduce operating expenses and conserve cash resources. The Company has also committed to retention payments payable to certain key employees if such employees remain with the Company until December 31, 2015 or are terminated by the Company without cause prior to such date. Restructuring charges for each period were as follows (in thousands): Three Months Nine Months 2015 2014 2015 2014 Employee severance and related costs $ 675 $ — $ 3,543 $ — Facility lease termination costs 1,127 — 1,127 — Asset impairments (21 ) — 192 — Total restructuring and asset impairment charges $ 1,781 $ — $ 4,862 $ — The accrued restructuring activity during the nine months ended September 30, 2015 was as follows: Employee Facility Total Accrued restructuring balance as of December 31, 2014 $ — $ — $ — Additional accruals 3,543 1,127 4,670 Cash payments (2,934 ) (1,127 ) (4,061 ) Accrued restructuring balance as of September 30, 2015 $ 609 $ — $ 609 The Company recorded the additional accruals as restructuring charges in the consolidated statements of operations. The accrued restructuring balance as of September 30, 2015, is presented as a current liability in the consolidated balance sheets and is expected to be paid within the fourth quarter of 2015. The charges incurred during the nine months ended September 30, 2015, included $2.4 million related to employee severance costs, which impacted 25 employees who were notified of their termination prior to September 30, 2015, $1.1 million related to retention payment accruals, and $1.1 million related to facility lease termination costs. The Company expects to record an additional $0.3 million related to retention payments in the fourth quarter of 2015. Following the announcement on June 26, 2015, that the Company had suspended further research and development of its MYDICAR programs, the Company determined that certain equipment used in the MYDICAR manufacturing process was impaired and an asset impairment charge of $0.2 million was recorded to restructuring charges in the consolidated statements of operations for the nine months ended September 30, 2015. The equipment was subsequently sold in September 2015. The Company may incur additional charges in connection with future restructuring activities.

Litigation

Litigation	9 Months Ended
	Sep. 30, 2015
Commitments and Contingencies Disclosure [Abstract]
Litigation	8. Litigation In July 2015, following the Company’s announcements of the negative CUPID 2 data and the suspension of further research and development activities and the subsequent declines of the price of the Company’s common stock, three putative securities class action complaints (captioned Fialkov v. Celladon Corporation, Case No. 15-cv-1458-AJB-DHB, Lorusso v. Celladon Corporation, Case No. 15-cv-1501-L-JLB and Jacobs v. Celladon Corporation, Case No. 15-cv-1529-AJB-MDD ) were filed in the U.S. District Court for the Southern District of California against the Company and certain of the Company’s current and former officers. The complaints generally allege that the defendants violated Sections 10(b) and 20(a) of the Securities Exchange Act of 1934 by making materially false and misleading statements regarding the clinical trial program for MYDICAR, thereby artificially inflating the price of the Company’s common stock. The complaints seek unspecified monetary damages and other relief, including attorneys’ fees. The Company expects the court to consolidate the three putative securities class actions and to appoint a lead plaintiff to represent the putative class. The Company then expects the lead plaintiff to file a consolidated complaint. It is possible that additional suits will be filed, or allegations made by stockholders, with respect to these same or other matters and also naming the Company and/or the Company’s officers and directors as defendants. The Company believes that it has meritorious defenses and intends to defend these lawsuits vigorously. Due to the early stage of these proceedings, the Company is not able to predict or reasonably estimate the ultimate outcome or possible losses relating to these claims.

Basis of Presentation, Organi21

Basis of Presentation, Organization and Summary of Significant Accounting Policies (Policies)	9 Months Ended	12 Months Ended
	Sep. 30, 2015	Dec. 31, 2014
Accounting Policies [Abstract]
Organization	Organization Celladon was incorporated in California on December 21, 2000 (inception) and reincorporated in Delaware in April 2012. The Company is a biotechnology company that has been focused on the development of cardiovascular gene therapy. As a consequence of the negative results from the Phase 2b clinical trial of its lead product candidate, MYDICAR (AAV1/SERCA2a), the Company is evaluating its strategic opportunities to maximize shareholder value, including the possibility of seeking a merger, sale of the Company or all or some of its assets, and/or a liquidation. At this time, the Company’s current development activities are limited to the oversight of the long-term follow up period in the CUPID 2 trial, which is expected to continue through February 2016. As of September 30, 2015, the Company has devoted substantially all of its efforts to product development, raising capital and building infrastructure and has not generated revenues from product sales or other sources.	Organization Celladon Corporation (Celladon or the Company) was incorporated in California on December 21, 2000 (inception) and reincorporated in Delaware in April 2012. The Company is a clinical-stage biotechnology with industry-leading expertise in the development of cardiovascular gene therapy. The Company applies its leadership position in the field of gene therapy and calcium dysregulation to develop novel therapies for diseases with tremendous unmet medical needs and characterized by an underlying SERCA enzyme deficiency. As of December 31, 2014, the Company has devoted substantially all of its efforts to product development, raising capital and building infrastructure and has not generated revenues from its planned principal operations.
Use of Estimates		Use of Estimates The Company’s consolidated financial statements are prepared in accordance with U.S. generally accepted accounting principles (GAAP). The preparation of the Company’s consolidated financial statements requires it to make estimates and assumptions that impact the reported amounts of assets, liabilities and expenses and the disclosure of contingent assets and liabilities in the Company’s consolidated financial statements and accompanying notes. The most significant estimates in the Company’s consolidated financial statements relate to the fair value of equity awards and clinical trial expense accruals. Although these estimates are based on the Company’s knowledge of current events and actions it may undertake in the future, actual results may ultimately materially differ from these estimates
Public Offerings		Public Offerings In February 2014, the Company completed its initial public offering of 6,325,000 shares of common stock at an offering price of $8.00 per share, which included the exercise by the underwriters of their option to purchase 825,000 additional shares of common stock. The Company received net proceeds of $44.3 million after deducting underwriting discounts and commission and offering expenses payable by the Company, including $1.7 million in offering costs paid by the Company prior to December 31, 2013. In connection with the initial public offering, all outstanding shares of convertible preferred stock were converted into shares of common stock, the outstanding principal and accrued interest on the Company’s outstanding convertible notes were converted into shares of common stock and the unamortized debt discount related to the convertible notes was charged to expense, warrants to purchase shares of Series A-1 preferred stock were converted into warrants to purchase common stock, the warrant liability was reclassified to additional paid-in capital, and the Company’s certificate of incorporation was amended and restated to authorize 200,000,000 shares of common stock and 10,000,000 shares of undesignated preferred stock. See Note 7 for additional information. In August 2014, the Company completed an underwritten public offering of 4,600,000 shares of common stock at an offering price of $9.50 per share, which included the exercise by the underwriters of their option to purchase 600,000 additional shares of common stock. The Company received net proceeds of $40.7 million after deducting underwriting discounts and commission and offering expenses payable by the Company. See Note 7 for additional information.
Principles of Consolidation	Principles of Consolidation The financial statements of the Company’s former subsidiary Celladon Europe B.V. (Celladon Europe) were consolidated with those of the Company through Celladon Europe’s dissolution on December 30, 2014. All intercompany transactions and balances were eliminated in consolidation.	Principles of Consolidation On April 27, 2012, Celladon formed a subsidiary, Celladon Europe B.V. (Celladon Europe), a Dutch limited liability company, for the purpose of managing the new capital investment made by Cooperatief LSP IV U.A. (LSP) related to Celladon’s Series A-1 preferred stock (see Note 2). From its inception to June 6, 2013 the subsidiary was 90% owned by Celladon and from June 6, 2013 to December 29, 2014 the subsidiary was wholly owned by Celladon. Celladon Europe was dissolved on December 30, 2014. The financial statements of Celladon Europe are consolidated with those of the Company. All intercompany transactions and balances were eliminated in consolidation. The U.S. dollar was the functional currency of Celladon Europe. The Company remeasured Celladon Europe’s assets and liabilities related to monetary assets and liabilities to the U.S. dollar and recorded the net gains or losses resulting from remeasurement in other income (expense) in the consolidated statements of operations and comprehensive loss. During all periods presented, the Company did not record any material gains or losses from remeasurement.
Segment Reporting		Segment Reporting Operating segments are identified as components of an enterprise about which separate discrete financial information is available for evaluation by the chief operating decision-maker in making decisions regarding resource allocation and assessing performance. The Company views its operations and manages its business in one operating segment.
Cash and Cash Equivalents		Cash and Cash Equivalents Cash and cash equivalents consists primarily of readily available checking, money market accounts and money market funds. The Company considers all highly liquid investments with an original maturity of three months or less at the date of purchase to be cash equivalents.
Investment Securities	Investment Securities Investment securities primarily consist of investment grade corporate debt securities. The Company classifies all investment securities as available-for-sale. Investments with maturity dates greater than 12 months from the end of each reporting period are classified as long-term. Investment securities are carried at fair value, with the unrealized gains and losses reported as a component of other comprehensive income (loss) in stockholders’ equity (deficit) until realized. Realized gains and losses from the sale of investment securities, if any, are determined on a specific identification basis. A decline in the market value of any investment security below cost that is determined to be other than temporary will result in an impairment charge to earnings and a new cost basis for the security is established. No such impairment charges were recorded for any period presented. As of December 31, 2014, none of the investment securities had been in an unrealized loss position for more than 12 months. Premiums and discounts are amortized or accreted over the life of the related security as an adjustment to yield using the straight-line method and are included in interest income. Interest income is recognized when earned. During the third quarter of 2015 the Company’s investment securities matured and the Company held the proceeds as cash equivalents. As of September 30, 2015, the Company had no investment securities. The following table sets forth the composition of the Company’s investment securities (in thousands) as of December 31, 2014: Unrealized As of December 31, 2014 Maturity in Years Amortized Gains Losses Fair Corporate debt securities Less than 1 year $ 70,521 $ — $ (8 ) $ 70,513	Investment Securities Investment securities primarily consist of investment grade corporate debt securities. The Company classifies all investment securities as available-for-sale. Investments with maturity dates greater than 12 months from the end of each reporting period are classified as long-term. Investment securities are carried at fair value, with the unrealized gains and losses reported as a component of other comprehensive income (loss) in stockholders’ equity (deficit) until realized. Realized gains and losses from the sale of investment securities, if any, are determined on a specific identification basis. A decline in the market value of any investment security below cost that is determined to be other than temporary will result in an impairment charge to earnings and a new cost basis for the security is established. No such impairment charges were recorded for any period presented. As of December 31, 2014 and December 31, 2013, none of the investment securities have been in an unrealized loss position for more than 12 months. Premiums and discounts are amortized or accreted over the life of the related security as an adjustment to yield using the straight-line method and are included in interest income. Interest income is recognized when earned. The following table sets forth the composition of the Company’s investment securities (in thousands): As of December 31, 2014 Maturity in Years Amortized Unrealized Fair Value Gains Losses Corporate debt securities Less than 1 year $ 70,521 $ — $ (8 ) $ 70,513 As of December 31, 2013 Maturity in Years Amortized Unrealized Fair Value Gains Losses Corporate debt securities Less than 1 year $ 10,465 $ 2 $ — $ 10,467
Concentration of Credit Risk		Concentration of Credit Risk Financial instruments, which potentially subject the Company to significant concentration of credit risk, consist primarily of cash, cash equivalents and investment securities. The Company has established guidelines regarding diversification of investments and their maturities, which are designed to maintain principal and maximize liquidity. The Company maintains deposits in federally insured financial institutions in excess of federally insured limits. The Company has not experienced any losses in such accounts and management believes that the Company is not exposed to significant credit risk due to the financial position of the depository institutions in which those deposits are held.
Property and Equipment		Property and Equipment Property and equipment are recorded at cost and depreciated using the straight-line method over the estimated useful lives of the assets (generally three to five years) and generally consist of furniture and fixtures, computers, and office equipment. Repairs and maintenance costs are charged to expense as incurred.
Impairment of Long-Lived Assets		Impairment of Long-Lived Assets Long-lived assets consist primarily of property and equipment. An impairment loss is recorded if and when events and circumstances indicate that assets might be impaired and the undiscounted cash flows estimated to be generated by those assets are less than the carrying amount of those assets. While the Company’s current and historical operating losses and negative cash flows are indicators of impairment, management believes that future cash flows to be received support the carrying value of its long-lived assets and, accordingly, has not recognized any impairment losses since inception.
Clinical Trial Accruals		Clinical Trial Accruals As part of the process of preparing its financial statements, the Company is required to estimate its expenses resulting from its obligations under contracts with vendors and consultants and clinical site agreements in connection with conducting clinical trials. The financial terms of these contracts are subject to negotiations which vary from contract to contract and may result in payment flows that do not match the periods over which materials or services are provided to the Company under such contracts. The Company’s objective is to reflect the appropriate trial expenses in its financial statements by matching those expenses with the period in which services and efforts are expended. The Company accounts for these expenses according to the progress of the trial as measured by patient progression and the timing of various aspects of the trial. The Company determines accrual estimates through financial models taking into account discussion with applicable personnel and outside service providers as to the progress or state of consummation of trials, or the services completed. During the course of a clinical trial, the Company adjusts its rate of clinical expense recognition if actual results differ from its estimates. The Company makes estimates of its accrued expenses as of each balance sheet date in its financial statements based on the facts and circumstances known at that time. Although the Company does not expect its estimates to be materially different from amounts actually incurred, its understanding of the status and timing of services performed relative to the actual status and timing of services performed may vary and may result in the Company reporting amounts that are too high or too low for any particular period. Through December 31, 2014, there have been no material adjustments to the Company’s prior period estimates of accrued expenses for clinical trials. The Company’s clinical trial accrual is dependent upon the timely and accurate reporting of contract research organizations and other third-party vendors.
Preferred Stock Warrant Liability		Preferred Stock Warrant Liability The Company had issued freestanding warrants to purchase shares of its convertible preferred stock. The fair value of these warrants is classified as a current liability at December 31, 2013 in the accompanying consolidated balance sheets since the underlying redeemable convertible preferred stock is classified as temporary equity at December 31, 2013 in the accompanying consolidated balance sheets instead of in stockholders’ equity (deficit) in accordance with authoritative guidance for the classification and measurement of redeemable securities. The warrants were recorded at fair value using the Black-Scholes option pricing model with any changes in fair value being recognized as a component of other income (expense) in the accompanying consolidated statements of operations and comprehensive loss. Upon completion of the Company’s initial public offering in February 2014, the warrants no longer required liability accounting and the then fair value of the warrant liability was reclassified into equity
Deferred Rent		Deferred Rent Deferred rent consists of the difference between cash payments and the recognition of rent expense on a straight-line basis for the facility the Company occupies. The Company’s lease for its facility provides for fixed increases in minimum annual rental payments. The total amount of rental payments due over the lease term is being charged to rent expense ratably over the life of the lease.
Preferred Stock		Preferred Stock The Company classifies preferred stock that is redeemable or subject to liquidation outside of the Company’s control outside of permanent equity. For preferred stock that is contractually redeemable outside of the Company’s control, the carrying value is increased to its redemption value by accretion in the period of issuance. In the absence of retained earnings, these accretion charges are recorded against additional paid-in capital.
Research and Development Costs		Research and Development Costs Research and development expenses consist primarily of salaries and related overhead expenses; fees paid to consultants and contract research organizations; costs related to acquiring and manufacturing clinical trial materials; costs related to compliance with regulatory requirements; and maintenance and license payments related to licensed product candidates and technologies. All research and development costs are expensed as incurred.
Patent Costs		Patent Costs Costs related to filing and pursuing patent applications are recorded as general and administrative expense and expensed as incurred since recoverability of such expenditures is uncertain.
Stock-Based Compensation		Stock-Based Compensation Stock-based compensation expense represents the cost of the grant date fair value of employee stock option grants and stock purchases under the Employee Stock Purchase Plan (ESPP) recognized over the requisite service period of the awards (usually the vesting period) on a straight-line basis, net of estimated forfeitures. The Company estimates the fair value of the awards using the Black-Scholes option pricing model. The Company accounts for stock options granted to non-employees using the fair value approach. These option grants are subject to periodic revaluation over their vesting terms.
Income Taxes		Income Taxes The Company accounts for income taxes under the asset and liability method, which requires the recognition of deferred tax assets and liabilities for the expected future tax consequences of events that have been included in the financial statements. Under this method, deferred tax assets and liabilities are determined on the basis of the differences between the financial statements and tax basis of assets and liabilities using enacted tax rates in effect for the year in which the differences are expected to reverse. The effect of a change in tax rates on deferred tax assets and liabilities is recognized in income in the period that includes the enactment date. The Company recognizes net deferred tax assets to the extent that management believes these assets are more likely than not to be realized. In making such a determination, management considers all available positive and negative evidence, including future reversals of existing taxable temporary differences, projected future taxable income, tax-planning strategies, and results of recent operations. If management determines that the Company would be able to realize its deferred tax assets in the future in excess of their net recorded amount, management would make an adjustment to the deferred tax asset valuation allowance, which would reduce the provision for income taxes. The Company records uncertain tax positions on the basis of a two-step process whereby (1) management determines whether it is more likely than not that the tax positions will be sustained on the basis of the technical merits of the position and (2) for those tax positions that meet the more-likely-than-not recognition threshold, management recognizes the largest amount of tax benefit that is more than 50% likely to be realized upon ultimate settlement with the related tax authority. The Company recognizes interest and penalties related to unrecognized tax benefits within income tax expense. Any accrued interest and penalties are included within the related tax liability.
Comprehensive Loss		Comprehensive Loss Comprehensive loss is defined as a change in equity during a period from transactions and other events and circumstances from non-owner sources. The Company’s only component of other comprehensive loss is unrealized gains (losses) on investment securities. Comprehensive loss has been reflected in the consolidated statements of operations and comprehensive loss and as a separate component of the statements of stockholders’ deficit for all periods presented.
Net Loss Per Share Attributable to Common Stockholders	Net Loss Per Share Attributable to Common Stockholders Basic and diluted net loss per common share is calculated by dividing net loss applicable to common stockholders by the weighted-average number of common shares outstanding during the period, without consideration for common stock equivalents. Potentially dilutive shares, which include convertible preferred stock and rights to acquire convertible preferred stock (non-controlling interest), warrants for the purchase of common stock and options outstanding under the Company’s equity incentive plans, are considered to be common stock equivalents and are only included in the calculation of diluted net loss per share when their effect is dilutive. Potentially dilutive securities not included in the calculation of diluted net loss per share attributable to common stockholders because to do so would be anti-dilutive are as follows (in common stock equivalent shares): Nine Months Ended 2015 2014 Warrants for common stock 152,735 206,340 Common stock options and restricted stock units 1,527,098 2,527,067 1,679,833 2,733,407	Net Loss Per Share Attributable to Common Stockholders Basic net loss per share attributable to common stockholders is calculated by dividing the net loss attributable to common stockholders by the weighted-average number of common shares outstanding for the period, without consideration for common stock equivalents. Diluted 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 common share equivalents outstanding for the period determined using the treasury-stock method. Dilutive common stock equivalents are comprised of convertible preferred stock and rights to acquire convertible preferred stock (non-controlling interest), warrants for the purchase of common stock and options outstanding under the Company’s stock option plans. For all periods presented, there is no difference in the number of shares used to calculate basic and diluted shares outstanding due to the Company’s net loss position. Potentially dilutive securities not included in the calculation of diluted net loss per share attributable to common stockholders because to do so would be anti-dilutive are as follows (in common stock equivalent shares): Years Ended December 31, 2014 2013 Redeemable convertible preferred stock — 10,179,372 Convertible preferred stock — 971,820 Warrants for convertible preferred stock — 231,821 Warrants for common stock 206,340 702 Common stock options 2,408,634 1,543,667 2,614,974 12,927,382
Recent Accounting Pronouncements	Recent Accounting Pronouncements In April 2015, the Financial Accounting Standards Board (the “FASB”) issued Accounting Standards Update (“ASU”) No. 2015-03, Interest - Imputation of Interest (Subtopic 835-30): Simplifying the Presentation of Debt Issuance Costs. The amendments in this ASU require that debt issuance costs related to a recognized debt liability be presented in the balance sheet as a direct deduction from the carrying amount of that debt liability, consistent with debt discounts. The amendments in this ASU are effective for financial statements issued for fiscal years beginning after December 15, 2015, and interim periods within those fiscal years. Early adoption of the amendments is permitted. The new guidance shall be applied on a retrospective basis, wherein the balance sheet of each individual period presented should be adjusted to reflect the period-specific effects of applying the new guidance. The Company is currently evaluating the impact of the adoption of this standard on its consolidated financial statements. In August 2014, the FASB issued ASU 2014-15, which defined management’s responsibility to evaluate whether there is substantial doubt about an entity’s ability to continue as a going concern and to provide related disclosure. ASU 2014-15 defined the term substantial doubt and requires an assessment for a period of one year after the date of the issuance of the financial statements. It requires certain disclosures when substantial doubt is alleviated as a result of consideration of management’s plans and requires an express statement and other disclosures when substantial doubt is not alleviated. The guidance becomes effective for reporting periods beginning after December 15, 2016, with early adoption permitted. The Company does not believe that the adoption of this guidance will have a material impact on its consolidated financial statements.	Recent Accounting Pronouncements In July 2013, the FASB issued Accounting Standards Update (ASU) No. 2013-11, Presentation of an Unrecognized Tax Benefit When a Net Operating Loss Carryforward, a Similar Tax Loss, or a Tax Credit Carryforward Exists In June 2014, the FASB issued Accounting Standards Update (ASU) No. 2014-10, Development Stage Entities (Topic 915): Elimination of Certain Financial Reporting Requirements, Including an Amendment to Variable Interest Entities Guidance in Topic 810, Consolidation 810-10-15-16 development stage entities In June 2014, the FASB issued ASU No. 2014-12, Accounting for Share-Based Payments When the Terms of an Award Provide That a Performance Target Could Be Achieved after the Requisite Service Period In August 2014, the FASB issued ASU No. 2014-15, Presentation of Financial Statements Going Concern In November 2014, the FASB issued ASU No. 2014-16, Determining Whether the Host Contract in a Hybrid Financial Instrument Issued in the Form of a Share is More Akin to Debt or Equity
Basis of Presentation	Basis of Presentation The accompanying unaudited consolidated financial statements of Celladon Corporation (Celladon or the Company) should be read in conjunction with the audited financial statements and notes thereto as of and for the year ended December 31, 2014 included in the Company’s Annual Report on Form 10-K (Annual Report) filed with the Securities and Exchange Commission (SEC). The accompanying financial statements have been prepared in accordance with U.S. generally accepted accounting principles (GAAP) for interim financial information and in accordance with the instructions to Form 10-Q and Article 10 of Regulation S-X. Accordingly, since they are interim statements, the accompanying financial statements do not include all of the information and notes required by GAAP for complete financial statements. In the opinion of management, the accompanying financial statements reflect all adjustments (consisting of normal recurring adjustments) that are necessary for a fair statement of the financial position, results of operations and cash flows for the interim periods presented. Interim results are not necessarily indicative of results for a full year. The preparation of the Company’s consolidated financial statements requires it to make estimates and assumptions that impact the reported amounts of assets, liabilities and expenses and the disclosure of contingent assets and liabilities in the Company’s consolidated financial statements and accompanying notes. The most significant estimates in the Company’s consolidated financial statements relate to the fair value of equity awards and clinical trial expense accruals. Although these estimates are based on the Company’s knowledge of current events and actions it may undertake in the future, actual results may ultimately materially differ from these estimates and assumptions.

Basis of Presentation, Organi22

Basis of Presentation, Organization and Summary of Significant Accounting Policies (Tables)	9 Months Ended	12 Months Ended
	Sep. 30, 2015	Dec. 31, 2014
Accounting Policies [Abstract]
Composition of Investment Securities	The following table sets forth the composition of the Company’s investment securities (in thousands) as of December 31, 2014: Unrealized As of December 31, 2014 Maturity in Years Amortized Gains Losses Fair Corporate debt securities Less than 1 year $ 70,521 $ — $ (8 ) $ 70,513	The following table sets forth the composition of the Company’s investment securities (in thousands): As of December 31, 2014 Maturity in Years Amortized Unrealized Fair Value Gains Losses Corporate debt securities Less than 1 year $ 70,521 $ — $ (8 ) $ 70,513 As of December 31, 2013 Maturity in Years Amortized Unrealized Fair Value Gains Losses Corporate debt securities Less than 1 year $ 10,465 $ 2 $ — $ 10,467
Potentially Dilutive Securities Not Included in Calculation of Diluted Net Loss Per Share Attributable to Common Stockholders	Potentially dilutive securities not included in the calculation of diluted net loss per share attributable to common stockholders because to do so would be anti-dilutive are as follows (in common stock equivalent shares): Nine Months Ended 2015 2014 Warrants for common stock 152,735 206,340 Common stock options and restricted stock units 1,527,098 2,527,067 1,679,833 2,733,407	Potentially dilutive securities not included in the calculation of diluted net loss per share attributable to common stockholders because to do so would be anti-dilutive are as follows (in common stock equivalent shares): Years Ended December 31, 2014 2013 Redeemable convertible preferred stock — 10,179,372 Convertible preferred stock — 971,820 Warrants for convertible preferred stock — 231,821 Warrants for common stock 206,340 702 Common stock options 2,408,634 1,543,667 2,614,974 12,927,382

Balance Sheet Details (Tables)

Balance Sheet Details (Tables)	9 Months Ended	12 Months Ended
	Sep. 30, 2015	Dec. 31, 2014
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Summary of Property and Equipment	Property and equipment consist of the following (in thousands): September 30, December 31, Office furniture and other equipment (1) $ 174 $ 881 Leasehold improvements (2) 246 246 Accumulated depreciation (1) (2) (287 ) (364 ) $ 133 $ 763 (1) Following the CUPID 2 trial results and the decision to not pursue additional previously planned development activities with MYDICAR, the Company sold certain MYDICAR manufacturing assets in the third quarter of 2015. The assets had a historical cost of $0.8 million and accumulated depreciation of $0.3 million. The Company had recognized an impairment charge of $0.2 million in the second quarter of 2015 related to the assets which had reduced the net asset value to $0.3 million, the amount of cash proceeds received (see Note 7). (2) In September 2015, in light of the scale-down of certain operations, the Company terminated a sublease agreement effective November 13, 2015, as amended, in order to reduce the Company’s office space and corresponding rent obligations. The sublease was originally scheduled to expire in September 2021. The Company revised the estimated depreciable life of the leasehold improvements associated with the facility to end on November 13, 2015. The change in estimated life resulted in an acceleration of depreciation expense in the amount of $0.1 million in the third quarter of 2015. The net book value of the leasehold improvements was $0.1 million at September 30, 2015.	Property and equipment consist of the following (in thousands): As of December 31, 2014 2013 Office furniture and other equipment $ 881 $ 555 Leasehold improvements 246 — Accumulated depreciation (364 ) (247 ) $ 763 $ 308
Summary of Accounts Payable and Accrued Expenses	Accounts payable and accrued expenses consist of the following (in thousands): September 30, December 31, Accounts payable $ 228 $ 3,293 Accrued compensation 93 1,909 Accrued other 547 596 Current portion of deferred rent 157 5 $ 1,025 $ 5,803	Accounts payable and accrued expenses consist of the following (in thousands): As of December 31, 2014 2013 Accounts payable $ 3,293 $ 1,397 Accrued compensation 1,909 664 Accrued other 596 839 Current portion of deferred rent 5 8 $ 5,803 $ 2,908
Summary of Prepaid Expenses and Other Assets	Prepaid expenses and other assets consist of the following (in thousands): September 30, December 31, Prepaid clinical expenses (1) $ 388 $ — Prepaid other expenses 546 756 Commercial manufacturing costs (2) — 1,751 Other receivables 67 628 $ 1,001 $ 3,135 (1) During the second half of 2015, following the reduction in workforce initiatives (see Note 7), the Company prepaid certain contract research organizations, or CROs, to manage most aspects of the ongoing CUPID2 trial, including the future payments to clinical sites for patient costs. Additionally, the Company prepaid $0.4 million to CROs in October 2015. (2) The commercial manufacturing costs consisted mainly of design and engineering services for commercial drug manufacturing capabilities. The Company determined that it was probable that it would not complete the commercial manufacturing project in light of the CUPID 2 clinical data announced in April 2015 (see Note 7). The Company therefore recorded the costs accumulated as of December 31, 2014 and activity in 2015 as a period expense in the consolidated financial statements in the nine month period ended September 30, 2015.

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	9 Months Ended	12 Months Ended
	Sep. 30, 2015	Dec. 31, 2014
Fair Value Disclosures [Abstract]
Summary of Assets and Liabilities Measured at Fair Value	Cash equivalents measured at fair value as of September 30, 2015 and December 31, 2014 are all classified within Level 1. As of September 30, 2015, the Company had no investment securities. Below is a summary of other assets and liabilities measured at fair value (in thousands): Fair Value Measurements at As of Quoted Prices Significant Significant Assets: Corporate debt securities $ 70,513 $ — $ 70,513 $ —	Cash equivalents measured at fair value as of December 31, 2014 and 2013, are all classified within Level 1. Below is a summary of assets and liabilities measured at fair value (in thousands): Fair Value Measurements at Reporting Date Using As of December 31, 2014 Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Assets: Corporate debt securities $ 70,513 $ — $ 70,513 $ — Fair Value Measurements at Reporting Date Using As of December 31, 2013 Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Assets: Corporate debt securities $ 10,467 $ — $ 10,467 $ — Liabilities: Convertible notes $ 1,044 — — $ 1,044 Warrant liability 1,116 — — 1,116 $ 2,160 $ — $ — $ 2,160
Reconciliation of All Liabilities Measured at Fair Value Using Level 3 Significant Unobservable Inputs		The following table provides a reconciliation of all liabilities measured at fair value using Level 3 significant unobservable inputs (in thousands): Redeemable Non-Controlling Interest Convertible Notes Warrant Liability Balance at December 31, 2011 $ — $ — $ — Issuance of shares of redeemable non-controlling interest 4,814 — — Net loss attributable to redeemable non-controlling interest (154 ) — — Change in fair value 154 — — Balance at December 31, 2012 4,814 — — Issuance of warrants in connection with note and warrant purchase agreement — — 954 Issuance of debt — 999 — Net loss attributable to redeemable non-controlling interest (96 ) — — Changes in fair value 3,105 45 162 Exchange of redeemable non-controlling interest for Series A-1 preferred stock (7,823 ) — — Balance at December 31, 2013 — 1,044 1,116 Changes in fair value — 53 183 Reclassification to equity upon initial public offering — — (1,299 ) Conversion to common stock upon initial public offering — (1,097 ) — Balance at December 31, 2014 $ — $ — $ —

Preferred Stock and Stockhold25

Preferred Stock and Stockholders' Equity (Deficit) (Tables)	9 Months Ended	12 Months Ended
	Sep. 30, 2015	Dec. 31, 2014
Summary of Authorized, Issued and Outstanding Shares of Preferred Stock by Series		The authorized, issued and outstanding shares of preferred stock by series are as follows (in thousands, except share amounts): Shares Authorized Shares Outstanding Liquidation Preference Redemption Amount As of December 31, 2014 Preferred stock 10,000,000 — — — As of December 31, 2013 Redeemable convertible preferred stock: Series A-1 135,826,497 127,140,530 $ 114,172 $ 57,086 Convertible preferred stock: Junior preferred stock 12,138,080 12,138,080 5,450 — Total 147,964,577 139,278,610 $ 119,622 $ 57,086
Summary of Proceeds Received and Costs Incurred in Connection with Company's Initial Public Offering		The proceeds received and costs incurred in connection with the Company’s initial public offering, shown in the period received or paid, were as follows (in thousands): Year ended December 31, Total 2014 2013 Gross proceeds (including over-allotment) $ 50,600 $ 50,600 $ — Underwriting discounts and commissions (3,542 ) (3,542 ) — Offering costs (2,800 ) (1,107 ) (1,693 ) Net proceeds $ 44,258 $ 45,951 $ (1,693 )
Summary of Proceeds Received and Costs Incurred in Connection with Company's Underwritten Public Offering		share. The proceeds received and costs incurred in connection with this offering, shown in the period received or paid, were as follows (in thousands): 2014 Gross proceeds (including option to purchase additional shares) $ 43,700 Underwriting discounts and commissions (2,622 ) Offering costs (389 ) Net proceeds $ 40,689
Summary of Company's Stock Option Activity		A summary of the Company’s stock option activity under the Prior Plans and 2013 Plan is as follows: Options Weighted- Average Exercise Price Per Share Weighted- Average Remaining Contractual Term Aggregate Intrinsic Value (in 000’s) Outstanding at December 31, 2013 1,543,667 $ 3.19 8.66 $ 9,128 Granted 1,240,673 10.61 Exercised (340,220 ) 1.20 Canceled (35,486 ) 10.93 Outstanding at December 31, 2014 2,408,634 $ 7.18 8.53 $ 31,031 Options exercisable at December 31, 2014 1,263,695 $ 4.02 7.78 $ 20,877 Options exercisable, vested and expected to vest at December 31, 2014 2,408,634 $ 7.18 8.53 $ 31,031
Schedule of Allocation of Stock-based Compensation for Equity Awards	The allocation of stock-based compensation for all equity awards is as follows (in thousands): Three Months Nine Months 2015 2014 2015 2014 Research and development (1) $ (663 ) $ 391 $ 929 $ 1,175 General and administrative 645 520 2,254 1,003 $ (18 ) $ 911 $ 3,183 $ 2,178 (1) During the three months ended September 30, 2015, following the reduction in workforce initiatives (see Note 7), the Company reversed the previously recorded expense for unvested options of terminated employees aggregating $0.8 million.	The allocation of stock-based compensation for all equity awards is as follows (in thousands): As of December 31, 2014 2013 2012 Research and development $ 1,712 $ 1,264 $ 222 General and administrative 1,607 124 76 $ 3,319 $ 1,388 $ 298
Summary of Common Stock Reserved for Future Issuance		Common stock reserved for future issuance as of December 31, 2014 and 2013 is as follows: December 31, 2014 2013 Granted and outstanding under the Plans 2,408,634 1,543,667 Available for grant under the 2012 Plan 294,845 26,294 Available for issuance under Employee Stock Purchase Plan 140,711 — Common stock warrants issued and outstanding 206,340 702 Convertible preferred stock warrants issued and outstanding — 231,821 Convertible preferred stock — 11,151,192 3,050,530 12,953,676
Summary of Exercisable Warrants Outstanding for Purchase of Common Stock	The following table summarizes the fully exercisable warrants outstanding for the purchase of common stock as of September 30, 2015 and December 31, 2014: September 30, 2015 December 31, 2014 Exercise Price Expiration Date 152,735 206,340 $ 5.61 October 2018
Summary of Company's Stock Option and RSU Activity	A summary of the Company’s stock option and RSU activity is as follows: Options and RSUs Outstanding at December 31, 2014 2,408,634 Granted 1,342,750 Exercised (383,011 ) Cancelled (1,841,275 ) Outstanding at September 30, 2015 1,527,098
Series A-1 Preferred Stock [Member]
Summary of Assumptions Used in Black-Scholes Option Pricing Model		In addition to the fair value of the underlying Series A-1 preferred stock, the following assumptions were used in the Black-Scholes option pricing model to determine the fair value of the preferred stock warrant liability: October 15, 2013 December 31, 2013 February 4, 2014 Risk-free interest rate 1.37 % 1.58 % 1.58 % Expected volatility 79 % 82 % 82 % Expected term (in years) 5.0 4.8 4.7 Expected dividend yield 0.0 % 0.0 % 0.0 %
Stock Options [Member]
Summary of Assumptions Used in Black-Scholes Option Pricing Model		The weighted-average assumptions used in the Black-Scholes option pricing model to determine the fair value of the employee stock option grants were as follows: As of December 31, 2014 2013 2012 Risk-free interest rate 1.90 % 1.62 % 2.29 % Expected volatility 80 % 79 % 84 % Expected term (in years) 6.0 5.6 5.9 Expected dividend yield 0.0 % 0.0 % 0.0 %

Commitments and Contingencies (

Commitments and Contingencies (Tables)	12 Months Ended
	Dec. 31, 2014
Commitments and Contingencies Disclosure [Abstract]
Schedule of Future Minimum Annual Rental Commitments Under Lease Obligations and Sublease Rental Receipts	The future minimum annual rental commitments under the lease obligations and sublease rental receipts at December 31, 2014 are as follows (in thousands): Lease Obligations Sublease Rental Receipts Total Year ending December 31: 2015 $ 466 $ (75 ) $ 391 2016 487 (77 ) 410 2017 485 (67 ) 418 2018 414 — 414 2019 426 — 426 Thereafter 776 — 776 Total $ 3,054 $ (219 ) $ 2,835

Long-Term Obligations (Tables)

Long-Term Obligations (Tables)	12 Months Ended
	Dec. 31, 2014
Debt Disclosure [Abstract]
Schedule of Future Contractual Principal and Final Fee Payments on Debt and Capital Lease Obligations	As of December 31, 2014, future contractual principal and final fee payments on the Company’s debt and capital lease obligations are as follows (in thousands): Year ending December 31: Total Term Loan Capital Lease 2015 $ 1 $ — $ 1 2016 3,432 3,430 2 2017 4,052 4,049 3 2018 4,275 4,271 4 2019 2 — 2 Total $ 11,762 $ 11,750 $ 12
Summary of Reconciliation of Future Contractual Principal and Final Fee Payments on Debt and Capital Lease Obligations	The following table provides a reconciliation of the Company’s future contractual principal and final fee payments on its debt and capital lease obligations to the reported carrying value as of December 31, 2014 (in thousands): Total loan debt and capital lease obligations $ 11,762 Less: Debt discount (1,659 ) Total carrying value: 10,103 Less: Carrying value of current portion of long-term obligations (1 ) Carrying value of long-term obligations, less current portion 10,102

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2014
Income Tax Disclosure [Abstract]
Schedule of Reconciliation of Expected Statutory Federal Income Tax Provision to Actual Income Tax Provision	The following is a reconciliation of the expected statutory federal income tax provision to the actual income tax provision (in thousands): December 31, 2014 2013 2012 Tax computed at federal statutory rate $ (11,510 ) $ (6,831 ) $ (5,396 ) State income tax, net of federal benefit (1,517 ) (987 ) (907 ) Non-deductible interest 20 20 36 Other permanent items 1,676 756 214 Research credits (557 ) (728 ) (93 ) Remove (restore) DTA for NOL and Credits – IRC 382 — (12,666 ) 2,135 State Taxes — — — Uncertain tax position (1,125 ) 859 — Valuation allowance 13,013 19,577 4,011 Provision (benefit) for income taxes $ — $ — $ —
Components of Deferred Tax Assets	The components of the Company’s deferred tax assets are summarized as follows (in thousands): December 31, 2014 2013 Deferred tax assets: Net operating loss carryforwards $ 31,484 $ 19,288 Research credits 1,649 1,092 Capitalized R&D 5,410 6,391 Other 2,049 803 Deferred tax assets 40,592 27,574 Valuation allowance (40,592 ) (27,574 ) Net deferred tax assets $ — $ —
Summary of Activity Related to Unrecognized Tax Benefits	The following table summarized the activity related to the Company’s unrecognized tax benefits (in thousands): Year Ended December 31, 2014 2013 Balance beginning of the year $ 1,709 $ — Increase related to prior year tax positions (1,361 ) 681 Increase related to current year tax positions 314 1,028 Balance at end of year $ 662 $ 1,709

Selected Quarterly Financial 29

Selected Quarterly Financial Data (Tables)	12 Months Ended
	Dec. 31, 2014
Quarterly Financial Information Disclosure [Abstract]
Summary of Quarterly Data	The following financial information reflects all normal recurring adjustments, which are, in the opinion of management, necessary for a fair statement of the results of the interim periods. Summarized quarterly data for fiscal 2014 and 2013 are as follows (in thousands, except per share data): First Quarter Second Quarter Third Quarter Fourth Quarter 2014 Total operating expenses $ 6,924 $ 7,005 $ 8,131 $ 10,958 Consolidated Net loss (7,162 ) (6,992 ) (8,358 ) (11,341 ) Basic and diluted net loss per share $ (0.60 ) $ (0.38 ) $ (0.40 ) $ (0.49 ) 2013 Total operating expenses $ 3,472 $ 4,992 $ 5,523 $ 5,977 Consolidated Net loss (3,530 ) (4,929 ) (5,453 ) (6,179 ) Basic and diluted net loss per share $ (3.99 ) $ (8.98 ) $ (6.17 ) $ (7.96 )

Restructuring charges (Tables)

Restructuring charges (Tables)	9 Months Ended
	Sep. 30, 2015
Restructuring and Related Activities [Abstract]
Schedule of Restructuring Charges	Restructuring charges for each period were as follows (in thousands): Three Months Nine Months 2015 2014 2015 2014 Employee severance and related costs $ 675 $ — $ 3,543 $ — Facility lease termination costs 1,127 — 1,127 — Asset impairments (21 ) — 192 — Total restructuring and asset impairment charges $ 1,781 $ — $ 4,862 $ —
Schedule of Accrued Restructuring Activity	The accrued restructuring activity during the nine months ended September 30, 2015 was as follows: Employee Facility Total Accrued restructuring balance as of December 31, 2014 $ — $ — $ — Additional accruals 3,543 1,127 4,670 Cash payments (2,934 ) (1,127 ) (4,061 ) Accrued restructuring balance as of September 30, 2015 $ 609 $ — $ 609

Basis of Presentation, Organi31

Basis of Presentation, Organization and Summary of Significant Accounting Policies - Additional Information (Detail)	Jun. 06, 2013	Aug. 31, 2014USD ($)$ / sharesshares	Feb. 28, 2014USD ($)$ / sharesshares	Sep. 30, 2015USD ($)Securitiesshares	Sep. 30, 2014USD ($)	Dec. 31, 2014USD ($)Segmentshares	Dec. 31, 2013USD ($)shares
Schedule of Available-for-sale Securities [Line Items]
Shares sold in initial public offering		4,600,000	6,325,000
Initial public offering price per share | $ / shares		$ 9.50	$ 8
Offering costs | $					$ 7,396,000	$ 7,661,000	$ 1,693,000
Authorized shares of common stock				200,000,000		200,000,000	180,000,000
Authorized shares of undesignated preferred stock				10,000,000		10,000,000	0
Number of operating segment | Segment						1
Impairment charges on investment securities | $				$ 0		$ 0
Investment securities, unrealized loss position for more than 12 months | $						$ 0	$ 0
Income tax benefit, likelihood of realized upon ultimate settlement						More than 50%
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Impairment charges on investment securities | $				$ 0		$ 0
Investment securities, unrealized loss position for more than 12 months | $						0
Number of investment securities | Securities				0
Celladon Europe [Member]
Schedule of Available-for-sale Securities [Line Items]
Ownership interest, percentage	90.00%
Initial Public Offering [Member]
Schedule of Available-for-sale Securities [Line Items]
Shares sold in initial public offering			6,325,000
Initial public offering price per share | $ / shares			$ 8
Underwriters option to purchase additional shares of common stock			825,000
Offering costs | $			$ 2,800,000			$ 1,107,000	$ 1,693,000
Proceeds from issuance of common stock, net | $			$ 44,300,000
Authorized shares of common stock			200,000,000
Authorized shares of undesignated preferred stock			10,000,000
Underwritten Public Offering [Member]
Schedule of Available-for-sale Securities [Line Items]
Shares sold in initial public offering		4,600,000
Initial public offering price per share | $ / shares		$ 9.50
Underwriters option to purchase additional shares of common stock		600,000
Proceeds from issuance of common stock, net | $		$ 40,700,000
Minimum [Member]
Schedule of Available-for-sale Securities [Line Items]
Property and equipment estimated useful lives of the assets						3 years
Maximum [Member]
Schedule of Available-for-sale Securities [Line Items]
Highly liquid investments original maturity period						3 months
Property and equipment estimated useful lives of the assets						5 years

Basis of Presentation, Organi32

Basis of Presentation, Organization and Summary of Significant Accounting Policies - Composition of Investment Securities (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013
Schedule of Available-for-sale Securities [Line Items]
Fair Value	$ 70,513	$ 10,467
Corporate Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Maturity in Years	Less than 1 year	Less than 1 year
Amortized Cost	$ 70,521	$ 10,465
Unrealized Gains	0	2
Unrealized Losses	(8)
Fair Value	$ 70,513	$ 10,467

Basis of Presentation, Organi33

Basis of Presentation, Organization and Summary of Significant Accounting Policies - Potentially Dilutive Securities Not Included in Calculation of Diluted Net Loss Per Share Attributable to Common Stockholders (Detail) - shares	9 Months Ended		12 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Dec. 31, 2014	Dec. 31, 2013
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive securities	1,679,833	2,733,407	2,614,974	12,927,382
Redeemable Convertible Preferred Stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive securities				10,179,372
Convertible Preferred Stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive securities				971,820
Warrants for Common Stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive securities	152,735	206,340	206,340	702
Common Stock Options and Restricted Stock Units [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive securities	1,527,098	2,527,067
Warrants for Convertible Preferred Stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive securities				231,821
Common Stock Options [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive securities			2,408,634	1,543,667

Celladon Europe B.V. - Addition

Celladon Europe B.V. - Additional Information (Detail) - USD ($) $ in Thousands	Jun. 06, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Feb. 04, 2014	Jun. 30, 2012	Apr. 30, 2012
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Shares issued for exchange of investment			11,151,192		11,151,192
Increases in fair value of redeemable non-controlling interest			$ (3,105)	$ (154)
Celladon Europe [Member]
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Increases in fair value of redeemable non-controlling interest			$ 3,100	$ 200
Cash Transferred from Celladon EU to Celladon US		$ 100
Celladon Europe [Member] | LSP [Member]
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Aggregate investment						$ 4,800	$ 4,800
Celladon Europe [Member] | Special Preferred Voting Stock [Member]
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Number of shares cancelled	1
Celladon Europe [Member] | Non-voting B Shares [Member]
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Shares issued for exchange of investment	1,999
Celladon Europe [Member] | Non-voting B Shares [Member] | LSP [Member]
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Shares issued for exchange of investment		1,999
Celladon Europe [Member] | Series A-1 Preferred Stock [Member]
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Number of shares exchanged at option	10,716,405
Celladon Europe [Member] | Series A-1 Preferred Stock [Member] | LSP [Member]
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Number of shares exchanged at option		10,716,405
Celladon Corporation [Member] | Special Preferred Voting Stock [Member] | LSP [Member]
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Shares issued for exchange of investment		1
Enterprise Transaction [Member] | LSP [Member]
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Ownership investment percentage	10.00%

Balance Sheet Details - Summary

Balance Sheet Details - Summary of Property and Equipment (Detail) - USD ($)		Sep. 30, 2015		Dec. 31, 2014		Dec. 31, 2013
Property, Plant and Equipment [Line Items]
Property and equipment, accumulated depreciation		$ (287,000)	[1],[2]	$ (364,000)	[1],[2]	$ (247,000)
Property and equipment, net		133,000		763,000		308,000
Office Furniture and Other Equipment [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross		170,000	[1]	881,000	[1]	$ 555,000
Leasehold Improvements [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	[2]	246,000		$ 246,000
Property and equipment, net		$ 100,000
[1]	Following the CUPID 2 trial results and the decision to not pursue additional previously planned development activities with MYDICAR, the Company sold certain MYDICAR manufacturing assets in the third quarter of 2015. The assets had a historical cost of $0.8 million and accumulated depreciation of $0.3 million. The Company had recognized an impairment charge of $0.2 million in the second quarter of 2015 related to the assets which had reduced the net asset value to $0.3 million, the amount of cash proceeds received (see Note 7).
[2]	In September 2015, in light of the scale-down of certain operations, the Company terminated a sublease agreement effective November 13, 2015, as amended, in order to reduce the Company's office space and corresponding rent obligations. The sublease was originally scheduled to expire in September 2021. The Company revised the estimated depreciable life of the leasehold improvements associated with the facility to end on November 13, 2015. The change in estimated life resulted in an acceleration of depreciation expense in the amount of $0.1 million in the third quarter of 2015. The net book value of the leasehold improvements was $0.1 million at September 30, 2015.

Balance Sheet Details - Summa36

Balance Sheet Details - Summary of Accounts Payable and Accrued Expenses (Detail) - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014	Dec. 31, 2013
Statement of Financial Position [Abstract]
Accounts payable	$ 228	$ 3,293	$ 1,397
Accrued compensation	93	1,909	664
Accrued other	547	596	839
Current portion of deferred rent	157	5	8
Accounts payable and accrued expenses	$ 1,025	$ 5,803	$ 2,908

Fair Value Measurements - Summa

Fair Value Measurements - Summary of Assets and Liabilities Measured at Fair Value (Detail) - USD ($) $ in Thousands	Dec. 31, 2014	Dec. 31, 2013
Liabilities:
Liabilities, Fair Value		$ 2,160
Corporate Debt Securities [Member]
Assets:
Assets, Fair Value	$ 70,513	10,467
Convertible Notes [Member]
Liabilities:
Liabilities, Fair Value		1,044
Warrant Liability [Member]
Liabilities:
Liabilities, Fair Value		$ 1,116
Level 1 [Member]
Liabilities:
Liabilities, Fair Value
Level 1 [Member] | Corporate Debt Securities [Member]
Assets:
Assets, Fair Value
Level 1 [Member] | Convertible Notes [Member]
Liabilities:
Liabilities, Fair Value
Level 1 [Member] | Warrant Liability [Member]
Liabilities:
Liabilities, Fair Value
Level 2 [Member]
Liabilities:
Liabilities, Fair Value
Level 2 [Member] | Corporate Debt Securities [Member]
Assets:
Assets, Fair Value	$ 70,513	$ 10,467
Level 2 [Member] | Convertible Notes [Member]
Liabilities:
Liabilities, Fair Value
Level 2 [Member] | Warrant Liability [Member]
Liabilities:
Liabilities, Fair Value
Level 3 [Member]
Liabilities:
Liabilities, Fair Value		$ 2,160
Level 3 [Member] | Corporate Debt Securities [Member]
Assets:
Assets, Fair Value
Level 3 [Member] | Convertible Notes [Member]
Liabilities:
Liabilities, Fair Value		$ 1,044
Level 3 [Member] | Warrant Liability [Member]
Liabilities:
Liabilities, Fair Value		$ 1,116

Fair Value Measurements - Addit

Fair Value Measurements - Additional Information (Detail) - $ / shares	Feb. 04, 2014	Oct. 15, 2013	Jun. 06, 2013	Dec. 31, 2013	Dec. 31, 2012
Series A-1 Preferred Stock [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of preferred stock per share derived from IPO	$ 0.640	$ 0.910	$ 0.730	$ 0.640	$ 0.449

Fair Value Measurements - Sum39

Fair Value Measurements - Summary of Assumptions used in Black-Scholes Option Pricing Model (Detail) - Series A-1 Preferred Stock [Member]	Feb. 04, 2014	Oct. 15, 2013	Dec. 31, 2013
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Risk-free interest rate	1.58%	1.37%	1.58%
Expected volatility	82.00%	79.00%	82.00%
Expected term (in years)	4 years 8 months 12 days	5 years	4 years 9 months 18 days
Expected dividend yield	0.00%	0.00%	0.00%

Fair Value Measurements - Recon

Fair Value Measurements - Reconciliation of All Liabilities Measured at Fair Value Using Level 3 Significant Unobservable Inputs (Detail) - Level 3 [Member] - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Convertible Notes [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance	$ 1,044
Issuance of warrants in connection with note and warrant purchase agreement
Issuance of shares of redeemable non-controlling interest
Issuance of debt		$ 999
Net loss attributable to redeemable non-controlling interest
Change in fair value	$ 53	$ 45
Reclassification to equity upon initial public offering
Conversion to common stock upon initial public offering	$ (1,097)
Ending balance		$ 1,044
Convertible Notes [Member] | Series A-1 Preferred Stock [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Exchange of redeemable non-controlling interest for Series A-1 preferred stock
Warrant Liability [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance	$ 1,116
Issuance of warrants in connection with note and warrant purchase agreement		$ 954
Issuance of shares of redeemable non-controlling interest
Issuance of debt
Net loss attributable to redeemable non-controlling interest
Change in fair value	183	$ 162
Reclassification to equity upon initial public offering	$ (1,299)
Conversion to common stock upon initial public offering
Ending balance		$ 1,116
Warrant Liability [Member] | Series A-1 Preferred Stock [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Exchange of redeemable non-controlling interest for Series A-1 preferred stock
Redeemable Non-Controlling Interest [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance		$ 4,814
Issuance of warrants in connection with note and warrant purchase agreement
Issuance of shares of redeemable non-controlling interest			$ 4,814
Issuance of debt
Net loss attributable to redeemable non-controlling interest		$ (96)	(154)
Change in fair value		$ 3,105	154
Reclassification to equity upon initial public offering
Conversion to common stock upon initial public offering
Ending balance			$ 4,814
Redeemable Non-Controlling Interest [Member] | Series A-1 Preferred Stock [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Exchange of redeemable non-controlling interest for Series A-1 preferred stock		$ (7,823)

Commitments and Contingencies -

Commitments and Contingencies - Additional Information (Detail)

Jul. 18, 2014USD ($)

Feb. 04, 2014USD ($)shares

Jun. 30, 2012USD ($)

Sep. 30, 2015USD ($)

Feb. 28, 2014USD ($)shares

Oct. 31, 2013USD ($)

Jun. 30, 2012USD ($)

May. 31, 2009USD ($)

Sep. 30, 2015USD ($)

Sep. 30, 2014USD ($)

Sep. 30, 2015USD ($)

Sep. 30, 2014USD ($)

Dec. 31, 2014USD ($)$ / sharesshares

Dec. 31, 2013USD ($)

Dec. 31, 2012USD ($)

Mar. 31, 2015ft²

Other Commitments [Line Items]

Convertible promissory notes, Accrued interest

$ 20,000

Number of shares issued on conversion of stock | shares

139,644

Fair value of warrants

$ 1,000,000

Warrants, exercise price | $ / shares

$ 5.61

Deemed dividend recognized

$ 856,000

Research and development expense

$ 738,000

$ 5,316,000

$ 21,757,000

$ 15,515,000

$ 22,676,000

16,927,000

$ 13,314,000

Payment in exchange for certain intangible assets associated with license agreement

$ 3,200,000

Rent expense

31,000

$ 94,000

300,000

136,000

Deferred rent expense

100,000

Future minimum payments under long-term operating leases

$ 51,000

51,000

$ 51,000

$ 2,835,000

Lease Agreements Two [Member]

Other Commitments [Line Items]

Long-term operating lease expiry period

2021-09

Sublease amended termination date

Nov. 13, 2015

Early termination fee

1,000,000

Lease Agreements One [Member]

Other Commitments [Line Items]

Long-term operating lease expiry period

2017-10

Short-term operating lease expiry period

2016-01

Lease Agreements Three [Member]

Other Commitments [Line Items]

Early termination fee

200,000

AmpliPhi Sublicense [Member]

Other Commitments [Line Items]

Sublicense initiation fee

$ 310,000

Aggregate potential milestone payments

850,000

Annual sublicense maintenance fee payable

310,000

310,000

Notice period given by company for termination of license agreement

30 days

License agreement expiration year

2,019

Research and development expense

$ 300,000

300,000

300,000

Milestone obligations incurred

0

Amended and Restated License Agreement [Member]

Other Commitments [Line Items]

Milestone obligations incurred

$ 0

Exclusive Patent License with the Regents of the University of Minnesota [Member]

Other Commitments [Line Items]

Notice period given by company for termination of license agreement

90 days

Research and development expense

$ 100,000

100,000

100,000

Milestone obligations incurred

$ 0

Upfront payment

$ 120,000

Annual license fee

120,000

Estimated future annual license fee

$ 325,000

License agreement termination, description

The Company may unilaterally terminate the agreement upon 90 days’ written notice to UMinn. UMinn may terminate the agreement upon 10 days’ written notice to the Company upon the Company’s insolvency or for its breach of the agreement if such breach remains uncured for 90 days after the Company receives notice of such breach, or 30 days in the case of a non-payment breach. Absent early termination, the agreement will automatically terminate upon the expiration of all active claims in any licensed patent or patent application, which is expected to occur no earlier than January 2030.

Patent expiration period

2030-01

Other License Agreements [Member]

Other Commitments [Line Items]

Research and development expense

$ 200,000

200,000

200,000

Aggregate potential future milestone payments

3,300,000

Aggregate minimum annual payments to maintain cancelable licenses

200,000

Licensing Agreements [Member] | AmpliPhi Sublicense Transaction [Member]

Other Commitments [Line Items]

Sublicense initiation fee

310,000

Annual sublicense maintenance fee payable

$ 310,000

310,000

Notice period given by company for termination of license agreement

30 days

License agreement expiration year

2,019

Research and development expense

$ 300,000

300,000

Milestone obligations incurred

0

Licensing Agreements [Member] | AmpliPhi Sublicense Transaction [Member] | Maximum [Member]

Other Commitments [Line Items]

Aggregate potential milestone payments

$ 850,000

Licensing Agreements [Member] | AmpliPhi Amended Sublicense Transaction [Member]

Other Commitments [Line Items]

Milestone obligations incurred

0

Licensing Agreements [Member] | Regents of University of Minnesota Patent Transaction [Member]

Other Commitments [Line Items]

Research and development expense

100,000

100,000

Milestone obligations incurred

0

Licensing Agreements [Member] | Other Transaction [Member]

Other Commitments [Line Items]

Research and development expense

200,000

$ 200,000

Aggregate potential future milestone payments

900,000

900,000

900,000

Aggregate minimum annual payments to maintain cancelable licenses

100,000

Licensing Agreements [Member] | Other Transaction [Member] | Milestone Obligations Agreement [Member]

Other Commitments [Line Items]

Research and development expense

$ 100,000

Milestone Obligations [Member]

Other Commitments [Line Items]

Research and development expense

$ 100,000

License Agreement Terms [Member]

Other Commitments [Line Items]

Notice period given by company for termination of license agreement

90 days

Upfront payment

$ 160,000

License agreement termination, description

Enterprise may terminate the agreement in the event of the Company's material breach of the Enterprise License Agreement if such breach remains uncured for 90 days following receipt of written notice of such breach.

Aggregate potential future milestone payments

$ 1,000,000

Royalty on net sales

2.00%

Long-term Operating Lease [Member]

Other Commitments [Line Items]

Long-term operating lease expiry period

2016-06

Rent expense

$ 300,000

$ 100,000

$ 100,000

Long-term Operating Lease [Member] | Lease Agreements Two [Member]

Other Commitments [Line Items]

Long-term operating lease expiry period

2021-09

Long-term Operating Lease [Member] | Lease Agreements One [Member]

Other Commitments [Line Items]

Long-term operating lease expiry period

2017-10

Operating lease expiry year

2,015

Long-term Operating Lease [Member] | Subsequent Event [Member]

Other Commitments [Line Items]

Area of office and laboratory space | ft²

7,000

Enterprise Transaction [Member] | Related Party [Member]

Other Commitments [Line Items]

Ownership interest, percentage

10.00%

Enterprise Transaction [Member] | Licensing Agreements [Member]

Other Commitments [Line Items]

Notice period given by company for termination of license agreement

90 days

Upfront payment

$ 160,000

License agreement termination, description

Enterprise may terminate the agreement in the event of the Company's material breach of the Enterprise License Agreement if such breach remains uncured for 90 days following receipt of written notice of such breach.

Ownership interest, percentage

10.00%

Aggregate potential future milestone payments

$ 1,000,000

$ 1,000,000

$ 1,000,000

Royalty on net sales

2.00%

Insolvency [Member] | Exclusive Patent License with the Regents of the University of Minnesota [Member]

Other Commitments [Line Items]

Notice period given to company for termination of license agreement company

10 days

Breach of Agreement [Member] | Exclusive Patent License with the Regents of the University of Minnesota [Member]

Other Commitments [Line Items]

Notice period given to company for termination of license agreement company

90 days

Non-payment Breach [Member] | Exclusive Patent License with the Regents of the University of Minnesota [Member]

Other Commitments [Line Items]

Notice period given to company for termination of license agreement company

30 days

Common Stock [Member]

Other Commitments [Line Items]

Number of shares issued on exercise warrants | shares

231,821

2013 Notes [Member]

Other Commitments [Line Items]

Convertible promissory notes issuable, Authorized

1,097,017

Convertible promissory notes, Fair value

$ 1,000,000

Convertible promissory notes, Accrued interest

$ 20,000

Number of shares issued on conversion of stock | shares

139,644

Deemed dividend recognized

$ 900,000

Commitments and Contingencies42

Commitments and Contingencies - Schedule of Future Minimum Annual Rental Commitments Under Lease Obligations and Sublease Rental Receipts (Detail) - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014
Operating Leased Assets [Line Items]
2,015		$ 391
2,016		410
2,017		418
2,018		414
2,019		426
Thereafter		776
Total	$ 51	2,835
Lease Obligations [Member]
Operating Leased Assets [Line Items]
2,015		466
2,016		487
2,017		485
2,018		414
2,019		426
Thereafter		776
Total		3,054
Sublease Rental Receipts [Member]
Operating Leased Assets [Line Items]
2,015		(75)
2,016		(77)
2,017		(67)
Total		$ (219)

Long-Term Obligations - Additio

Long-Term Obligations - Additional Information (Detail)

Feb. 01, 2018USD ($)

Aug. 03, 2015USD ($)

Jun. 30, 2015USD ($)

Aug. 01, 2014USD ($)

Sep. 30, 2015USD ($)

Sep. 30, 2014USD ($)

Sep. 30, 2015USD ($)Payments

Sep. 30, 2014USD ($)

Dec. 31, 2014USD ($)$ / shares

Dec. 31, 2013USD ($)

Dec. 31, 2012USD ($)

Jul. 31, 2014USD ($)

Debt Instrument [Line Items]

Loan fees

$ 1,750,000

$ 334,000

$ 387,000

Interest expense

$ 1,347,000

$ 271,000

$ 2,302,000

$ 330,000

$ 741,000

$ 59,000

$ 108,000

Convertible Debt [Member]

Debt Instrument [Line Items]

Interest expense

$ 100,000

$ 100,000

Capital Lease Obligations [Member]

Debt Instrument [Line Items]

Capital lease, number of payments | Payments

60

Capital lease obligations

$ 600

Hercules Loan Agreement [Member]

Debt Instrument [Line Items]

Loan agreement, terms on interest rate calculation

The Loan accrued interest at a rate equal to the greater of either (i) 8.25% plus the prime rate as reported from time to time in The Wall Street Journal minus 5.25%, and (ii) 8.25%. Contractual payments under the Loan Agreement were interest only until August 1, 2015

Loan agreement, interest rate during the period

8.25%

8.25%

Loan agreement, milestone description

In April 2015, the Company's senior management and board of directors determined that the Company did not achieve the Milestone (see Note 7). Accordingly, the Company could not draw down the second tranche of $15.0 million.

Outstanding principal balance

$ 10,000,000

Accrued and unpaid interest

75,625

End of term charge

1,750,000

Debt instrument prepayment date

Aug. 3, 2015

Total payment of debt

$ 11,825,625

Hercules Loan Agreement [Member] | Prime Rate [Member]

Debt Instrument [Line Items]

Loan agreement, percentage to be reduced from interest rate under condition

(5.25%)

Hercules Loan Agreement [Member] | First Tranche [Member]

Debt Instrument [Line Items]

Loan agreement, maximum borrowing capacity

$ 25,000,000

Loan agreement, amount borrowed

$ 10,000,000

Hercules Loan Agreement [Member] | Second Tranche [Member]

Debt Instrument [Line Items]

Loan agreement, amount borrowed

$ 15,000,000

Expiration date of tranche

Jun. 30, 2015

Scenario, Forecast [Member] | Hercules Loan Agreement [Member]

Debt Instrument [Line Items]

Loan fees

$ 1,750,000

Hercules Technology III L.P. and Hercules Technology Growth Capital, Inc. [Member]

Debt Instrument [Line Items]

Loan agreement, terms on interest rate calculation

The interest rate for each tranche will be calculated at a rate equal to the greater of either (i) 8.25% plus the prime rate as reported from time to time in The Wall Street Journal minus 5.25%, and (ii) 8.25%. Payments under the Loan Agreement are interest only until August 1, 2015 (which will be extended until February 1, 2016 if the Company achieves the Milestone on or before June 30, 2015)

Loan agreement, interest rate during the period

8.25%

Prepayment charge

1.50%

Maximum convertible limit of principal installment

$ 3,000,000

Conversion price | $ / shares

$ 16.33

Addition in interest rate on default

5.00%

Interest expense

$ 700,000

Hercules Technology III L.P. and Hercules Technology Growth Capital, Inc. [Member] | Prime Rate [Member]

Debt Instrument [Line Items]

Loan agreement, percentage to be reduced from interest rate under condition

(5.25%)

Hercules Technology III L.P. and Hercules Technology Growth Capital, Inc. [Member] | First Tranche [Member]

Debt Instrument [Line Items]

Loan agreement, maximum borrowing capacity

$ 25,000,000

Loan agreement, amount borrowed

10,000,000

Loan fees

150,000

Loan agreement, commitment fee paid

$ 37,500

Hercules Technology III L.P. and Hercules Technology Growth Capital, Inc. [Member] | Second Tranche [Member]

Debt Instrument [Line Items]

Expiration date of tranche

Jun. 30, 2015

Hercules Technology III L.P. and Hercules Technology Growth Capital, Inc. [Member] | Scenario, Forecast [Member]

Debt Instrument [Line Items]

Loan fees

$ 1,750,000

Hercules Technology III L.P. and Hercules Technology Growth Capital, Inc. [Member] | Scenario, Forecast [Member] | Second Tranche [Member]

Debt Instrument [Line Items]

Loan fees

100,000

Loan agreement, amount borrowed

$ 15,000,000

Long-Term Obligations - Schedul

Long-Term Obligations - Schedule of Future Contractual Principal and Final Fee Payments on Debt and Capital Lease Obligations (Detail) $ in Thousands	Dec. 31, 2014USD ($)
Debt Instruments [Abstract]
2,015	$ 1
2,016	3,432
2,017	4,052
2,018	4,275
2,019	2
Total	11,762
Term Loan, 2015	0
Term Loan, 2016	3,430
Term Loan, 2017	4,049
Term Loan, 2018	4,271
Term Loan, 2019	0
Term Loan, Total	11,750
Capital Lease, 2015	1
Capital Lease, 2016	2
Capital Lease, 2017	3
Capital Lease, 2018	4
Capital Lease, 2019	2
Capital Lease, Total	$ 12

Long-Term Obligations - Summary

Long-Term Obligations - Summary of Reconciliation of Future Contractual Principal and Final Fee Payments on Debt and Capital Lease Obligations (Detail) $ in Thousands	Dec. 31, 2014USD ($)
Debt Instruments [Abstract]
Total loan debt and capital lease obligations	$ 11,762
Less: Debt discount	(1,659)
Total carrying value:	10,103
Less: Carrying value of current portion of long-term obligations	(1)
Carrying value of long-term obligations, less current portion	10,102
Total carrying value:	$ 10,103

Preferred Stock and Stockhold46

Preferred Stock and Stockholders' Equity (Deficit) - Additional Information (Detail) - USD ($)	Feb. 04, 2014	Aug. 31, 2014	Feb. 28, 2014	Jan. 31, 2014	Sep. 30, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Sep. 30, 2014
Class of Stock [Line Items]
Preferred stock converted into common stock	11,151,192						11,151,192
Shares sold in initial public offering		4,600,000	6,325,000
Initial public offering price per share		$ 9.50	$ 8
Preferred stock, shares outstanding					0	0	0
Convertible promissory notes, Accrued interest	$ 20,000
Convertible promissory notes converted into common stock	139,644
Shares reserved for issuance						3,050,530	12,953,676
Common stock reserved for issuance, description					The number of shares of common stock reserved for issuance will automatically increase on January 1 of each calendar year through January 1, 2023 by the least of (1) 1% of the total number of shares of the Company's common stock outstanding on December 31 of the preceding calendar year, (2) 384,307 shares, or (3) a number determined by the Company's board of directors that is less than (1) and (2).	The number of shares of common stock reserved for issuance will automatically increase on January 1 of each calendar year, from January 1, 2015 through January 1, 2023 by the least of (1) 1% of the total number of shares of the Company's common stock outstanding on December 31 of the preceding calendar year, (2) 384,307 shares, or (3) a number determined by the Company's board of directors that is less than (1) and (2).
Weighted-average grant date fair value of employee option grants						$ 7.36	$ 7.27	$ 0.75
Aggregate intrinsic value of options exercised						$ 3,900,000
Options exercised						340,220
Stock-based compensation expense						$ 3,319,000	$ 1,388,000	$ 298,000
Unrecognized compensation cost					$ 7,300,000	$ 8,900,000
Unrecognized compensation cost expected to be recognized as expense period					2 years 10 months 24 days	3 years
Series A-1 Redeemable Convertible Preferred Stock [Member]
Class of Stock [Line Items]
Preferred stock converted into common stock	971,820
Preferred stock, shares outstanding	127,140,530
Junior Preferred Convertible Stock [Member]
Class of Stock [Line Items]
Preferred stock converted into common stock	10,179,372
Preferred stock, shares outstanding	12,138,080
Series A-1 Preferred Stock [Member]
Class of Stock [Line Items]
Conversion of warrants	2,895,570
Common Stock [Member]
Class of Stock [Line Items]
Shares sold in initial public offering						4,600,000
Conversion of warrants	231,821
Options exercised						340,220
Prior to initial public offering in 2014 [Member]
Class of Stock [Line Items]
Options exercised							0
Common Stock Options [Member] | Maximum [Member]
Class of Stock [Line Items]
Options, expiration Period					10 years	10 years
Common Stock Options [Member] | Minimum [Member]
Class of Stock [Line Items]
Options, vesting period					4 years	4 years
Promissory Notes [Member]
Class of Stock [Line Items]
Convertible promissory notes, Principle balance outstanding	$ 1,097,017
Prior Plans [Member] | Common Stock Options [Member]
Class of Stock [Line Items]
Shares available for grant					0				0
2013 Equity Incentive Plan [Member]
Class of Stock [Line Items]
Common stock authorized for issuance			1,473,738
Percentage of common stock outstanding to increase shares reserved for issuance			5.00%
Common stock reserved for issuance, description					Additionally, the 2013 Equity Incentive Plan provides for the grant of performance cash awards. The number of shares of common stock reserved for issuance under the 2013 Equity Incentive Plan will automatically increase on January 1 of each year continuing through and including January 1, 2023 by 5% of the total number of shares of the Company's capital stock outstanding on December 31 of the preceding calendar year, or a lesser number of shares determined by the Company's board of directors.	Additionally, the 2013 Plan provides for the grant of performance cash awards. Initially, the aggregate number of shares of common stock that may be issued pursuant to stock awards under the 2013 Plan is the sum of (1) 1,473,738 shares, plus (2) the number of shares (not to exceed 1,569,905 shares) (i) the 26,294 shares reserved for issuance under the 2012 Plan at the time the 2013 Plan became effective, and (ii) any shares subject to outstanding stock options or other stock awards that were granted under the Prior Plans that are forfeited, terminate, expire or are otherwise not issued. Additionally, the number of shares of common stock reserved for issuance under the 2013 Plan will automatically increase on January 1 of each year, beginning on January 1, 2015 and continuing through and including January 1, 2023, by 5% of the total number of shares of the Company’s capital stock outstanding on December 31 of the preceding calendar year, or a lesser number of shares determined by the Company’s board of directors.
2013 Equity Incentive Plan [Member] | Maximum [Member]
Class of Stock [Line Items]
Common stock authorized for issuance			1,569,905
2012 Equity Incentive Plan [Member]
Class of Stock [Line Items]
Shares reserved for issuance			26,294
2013 Employee Stock Purchase Plan [Member]
Class of Stock [Line Items]
Common stock authorized for issuance			165,732
Percentage of common stock outstanding to increase shares reserved for issuance			1.00%	1.00%
Stock-based compensation expense						$ 100,000
2013 Employee Stock Purchase Plan [Member] | Maximum [Member]
Class of Stock [Line Items]
Common stock authorized for issuance			384,307	384,307

Preferred Stock and Stockhold47

Preferred Stock and Stockholders' Equity (Deficit) - Summary of Authorized, Issued and Outstanding Shares of Preferred Stock by Series (Detail) - USD ($) $ in Thousands	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Temporary Equity [Line Items]
Shares Authorized		147,964,577
Shares Outstanding		139,278,610
Liquidation Preference		$ 119,622
Redemption Amount		$ 57,086
Preferred Stock [Member]
Temporary Equity [Line Items]
Shares Authorized	10,000,000
Series A-1 Redeemable Convertible Preferred Stock [Member]
Temporary Equity [Line Items]
Shares Authorized	0	135,826,497
Shares Outstanding	0	127,140,530	116,424,125
Liquidation Preference	$ 0	$ 114,172
Redemption Amount		$ 57,086
Junior Preferred Stock [Member]
Temporary Equity [Line Items]
Shares Authorized		12,138,080
Shares Outstanding		12,138,080
Liquidation Preference		$ 5,450

Preferred Stock and Stockhold48

Preferred Stock and Stockholders' Equity (Deficit) - Summary of Proceeds Received and Costs Incurred in Connection with Company's Initial Public Offering (Detail) - USD ($) $ in Thousands	1 Months Ended	9 Months Ended		12 Months Ended
	Feb. 28, 2014	Sep. 30, 2015	Sep. 30, 2014	Dec. 31, 2014	Dec. 31, 2013
Initial Public Offering [Line Items]
Gross proceeds (including over-allotment)		$ 783	$ 94,578	$ 95,028
Offering costs			$ (7,396)	(7,661)	$ (1,693)
Initial Public Offering [Member]
Initial Public Offering [Line Items]
Gross proceeds (including over-allotment)	$ 50,600			50,600
Underwriting discounts and commissions	(3,542)			(3,542)
Offering costs	(2,800)			(1,107)	(1,693)
Net proceeds	$ 44,258			$ 45,951	$ (1,693)

Preferred Stock and Stockhold49

Preferred Stock and Stockholders' Equity (Deficit) - Summary of Proceeds Received and Costs Incurred in Connection with Company's Underwritten Public Offering (Detail) - USD ($) $ in Thousands	1 Months Ended	9 Months Ended		12 Months Ended
	Aug. 31, 2014	Sep. 30, 2015	Sep. 30, 2014	Dec. 31, 2014	Dec. 31, 2013
Initial Public Offering [Line Items]
Gross proceeds (including option to purchase additional shares)		$ 783	$ 94,578	$ 95,028
Offering costs			$ (7,396)	$ (7,661)	$ (1,693)
Net proceeds	$ 40,689
Underwritten Public Offering [Member]
Initial Public Offering [Line Items]
Gross proceeds (including option to purchase additional shares)	43,700
Underwriting discounts and commissions	(2,622)
Offering costs	$ (389)

Stockholders' Equity - Summary

Stockholders' Equity - Summary of Exercisable Warrants Outstanding for Purchase of Common Stock (Detail) - $ / shares	9 Months Ended	12 Months Ended
	Sep. 30, 2015	Dec. 31, 2014	Dec. 31, 2013
Class of Warrant or Right [Line Items]
Warrants outstanding		206,340	702
Warrants outstanding, Exercise Price		$ 5.61
October 2018 [Member]
Class of Warrant or Right [Line Items]
Warrants outstanding	152,735	206,340
Warrants outstanding, Exercise Price	$ 5.61	$ 5.61
Warrants outstanding, Expiration Date	2018-10	2018-10
January 2015 [Member]
Class of Warrant or Right [Line Items]
Warrants outstanding			80
Warrants outstanding, Exercise Price		$ 224.82
Warrants outstanding, Expiration Date		2015-01
October 2016 [Member]
Class of Warrant or Right [Line Items]
Warrants outstanding			622
Warrants outstanding, Exercise Price		$ 12.49
Warrants outstanding, Expiration Date		2016-10

Preferred Stock and Stockhold51

Preferred Stock and Stockholders' Equity (Deficit) - Summary of Company's Stock Option Activity (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013
Equity [Abstract]
Options, Outstanding at beginning	1,543,667
Options, Granted	1,240,673
Options, Exercised	(340,220)
Options, Canceled	(35,486)
Options, Outstanding at ending	2,408,634	1,543,667
Options, Options exercisable	1,263,695
Options, Options exercisable, vested and expected to vest	2,408,634
Weighted-Average Exercise Price, Outstanding, Beginning balance	$ 3.19
Weighted-Average Exercise Price, Granted	10.61
Weighted-Average Exercise Price, Exercised	1.20
Weighted-Average Exercise Price, Canceled	10.93
Weighted-Average Exercise Price, Outstanding, Ending balance	7.18	$ 3.19
Weighted-Average Exercise Price, Options exercisable	4.02
Options exercisable, vested and expected to vest	$ 7.18
Weighted-Average Remaining Contractual Term, Outstanding, Balance	8 years 6 months 11 days	8 years 7 months 28 days
Weighted-Average Remaining Contractual Term, Options exercisable	7 years 9 months 11 days
Weighted-Average Remaining Contractual Term, Options exercisable, vested and expected to vest	8 years 6 months 11 days
Aggregate Intrinsic, Outstanding, Beginning Balance	$ 9,128
Aggregate Intrinsic, Outstanding, Ending Balance	31,031	$ 9,128
Aggregate Intrinsic, Outstanding, Options exercisable	20,877
Aggregate Intrinsic, Outstanding, Options exercisable, vested and expected to vest	$ 31,031

Preferred Stock and Stockhold52

Preferred Stock and Stockholders' Equity (Deficit) - Weighted-Average Assumptions Used in Black-Scholes Option Pricing Model to Determine Fair Value of Employee Stock Option Grants (Detail)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Equity [Abstract]
Risk-free interest rate	1.90%	1.62%	2.29%
Expected volatility	80.00%	79.00%	84.00%
Expected term (in years)	6 years	5 years 7 months 6 days	5 years 10 months 24 days
Expected dividend yield	0.00%	0.00%	0.00%

Preferred Stock and Stockhold53

Preferred Stock and Stockholders' Equity (Deficit) - Schedule of Allocation of Stock-based Compensation for Equity Awards (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	$ 3,319	$ 1,388	$ 298
Research and Development [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	1,712	1,264	222
General and Administrative [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	$ 1,607	$ 124	$ 76

Preferred Stock and Stockhold54

Preferred Stock and Stockholders' Equity (Deficit) - Summary of Common Stock Reserved for Future Issuance (Detail) - shares	Dec. 31, 2014	Feb. 04, 2014	Dec. 31, 2013
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Granted and outstanding under the Plans	2,408,634		1,543,667
Warrants issued and outstanding	206,340		702
Convertible preferred stock		11,151,192	11,151,192
Available for grant under the Plan	3,050,530		12,953,676
Warrants for Common Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Warrants issued and outstanding	206,340		702
Convertible Preferred Stock Warrants [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Warrants issued and outstanding			231,821
Two Thousand And Twelve Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Available for grant under the Plan	294,845		26,294
Employee Stock Purchase Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Available for grant under the Plan	140,711

Income Taxes - Schedule of Reco

Income Taxes - Schedule of Reconciliation of Expected Statutory Federal Income Tax Provision to Actual Income Tax Provision (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Income Tax Disclosure [Abstract]
Tax computed at federal statutory rate	$ (11,510)	$ (6,831)	$ (5,396)
State income tax, net of federal benefit	(1,517)	(987)	(907)
Non-deductible interest	20	20	36
Other permanent items	1,676	756	214
Research credits	(557)	(728)	(93)
Remove (restore) DTA for NOL and Credits - IRC 382		(12,666)	2,135
State Taxes	0	0	0
Uncertain tax position	(1,125)	859
Valuation allowance	13,013	19,577	4,011
Provision (benefit) for income taxes	$ 0	$ 0	$ 0

Income Taxes - Components of De

Income Taxes - Components of Deferred Tax Assets (Detail) - USD ($) $ in Thousands	Dec. 31, 2014	Dec. 31, 2013
Deferred tax assets:
Net operating loss carryforwards	$ 31,484	$ 19,288
Research credits	1,649	1,092
Capitalized R&D	5,410	6,391
Other	2,049	803
Deferred tax assets	40,592	27,574
Valuation allowance	(40,592)	(27,574)
Net deferred tax assets	$ 0	$ 0

Income Taxes - Additional Infor

Income Taxes - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Income Taxes [Line Items]
Valuation allowance	$ 40,592,000	$ 27,574,000
Valuation allowance recognized to offset the deferred tax assets	$ 13,013,000	19,577,000	$ 4,011,000
Net operating loss and research tax credit carry forwards utilization period	3 years
Unrecognized tax benefits	$ 662,000	$ 1,709,000
Unrecognized tax benefits impact on effective tax rate	700,000
Accrued interest and penalties associated with uncertain tax positions	0
Federal [Member]
Income Taxes [Line Items]
Net operating loss carryforwards	$ 82,200,000
Net operating loss carryforwards expiration year	2,027
Minimum [Member]
Income Taxes [Line Items]
Net operating loss and research tax credit carry forwards ownership percentage change for utilization	50.00%
California [Member]
Income Taxes [Line Items]
Net operating loss carryforwards	$ 77,000,000
Research [Member] | Federal [Member]
Income Taxes [Line Items]
Tax credits expiration year	2,032
Research [Member] | State [Member]
Income Taxes [Line Items]
Tax credits	$ 1,300,000
Research [Member] | California [Member]
Income Taxes [Line Items]
Tax credits expiration description	Indefinitely until utilized.

Income Taxes - Summary of Activ

Income Taxes - Summary of Activity Related to Unrecognized Tax Benefits (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013
Income Tax Disclosure [Abstract]
Balance beginning of the year	$ 1,709
Increase related to prior year tax positions	(1,361)	$ 681
Increase related to current year tax positions	314	1,028
Balance at end of year	$ 662	$ 1,709

Employee Benefits - Additional

Employee Benefits - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Defined Contribution Pension and Other Postretirement Plans Disclosure [Abstract]
Employee benefits plan, employer matching contribution	$ 0.3	$ 0.1	$ 0.1
Description of 401(k) plan	All employees of the Company are eligible to participate in the 401(k) Plan. The 401(k) matching contributions, if any, are determined by the Company at its sole discretion.

Subsequent Event - Additional I

Subsequent Event - Additional Information (Detail) - Manufacturing Agreement [Member] - EUR (€)	12 Months Ended
	Dec. 31, 2014	Mar. 20, 2015
Subsequent Event [Line Items]
Agreement entered date	Mar. 20, 2015
Extended agreement expiration date	2,020
Agreement termination description	The Company has the right to terminate the Manufacturing Agreement (i) at will on or before March 31, 2016, (ii) following the shut-down or non-production of the Novasep Facility for a specified period of time, or (iii) upon Novasep's debarment.
Minimum [Member]
Subsequent Event [Line Items]
Agreement expiration date	Dec. 31, 2018
Subsequent Event [Member] | Maximum [Member]
Subsequent Event [Line Items]
Payment agreed under agreement		€ 4,750,000

Selected Quarterly Financial 61

Selected Quarterly Financial Data - Summary of Quarterly Data (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended									9 Months Ended		12 Months Ended
	Sep. 30, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Sep. 30, 2015	Sep. 30, 2014	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Quarterly Financial Information Disclosure [Abstract]
Total operating expenses	$ 5,052	$ 10,958	$ 8,131	$ 7,005	$ 6,924	$ 5,977	$ 5,523	$ 4,992	$ 3,472	$ 37,424	$ 22,060	$ 33,018	$ 19,964	$ 15,945
Consolidated net loss	$ (6,396)	$ (11,341)	$ (8,358)	$ (6,992)	$ (7,162)	$ (6,179)	$ (5,453)	$ (4,929)	$ (3,530)	$ (39,667)	$ (22,512)	$ (33,853)	$ (20,091)	$ (15,871)
Basic and diluted net loss per share	$ (0.27)	$ (0.49)	$ (0.40)	$ (0.38)	$ (0.60)	$ (7.96)	$ (6.17)	$ (8.98)	$ (3.99)	$ (1.66)	$ (1.32)	$ (1.82)	$ (27.09)	$ (19.74)

Balance Sheet Details - Summa62

Balance Sheet Details - Summary of Prepaid Expenses and Other Assets (Detail) - USD ($) $ in Thousands		Sep. 30, 2015	Dec. 31, 2014	Dec. 31, 2013
Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract]
Prepaid clinical expenses	[1]	$ 388
Prepaid other expenses		546	$ 756
Commercial manufacturing costs	[2]		1,751
Other receivables		67	628
Prepaid expenses and other assets		$ 1,001	$ 3,135	$ 180
[1]	During the second half of 2015, following the reduction in workforce initiatives (see Note 7), the Company prepaid certain contract research organizations, or CROs, to manage most aspects of the ongoing CUPID2 trial, including the future payments to clinical sites for patient costs. Additionally, the Company prepaid $0.4 million to CROs in October 2015.
[2]	The commercial manufacturing costs consisted mainly of design and engineering services for commercial drug manufacturing capabilities. The Company determined that it was probable that it would not complete the commercial manufacturing project in light of the CUPID 2 clinical data announced in April 2015 (see Note 7). The Company therefore recorded the costs accumulated as of December 31, 2014 and activity in 2015 as a period expense in the consolidated financial statements in the nine month period ended September 30, 2015.

Balance Sheet Details - Summa63

Balance Sheet Details - Summary of Prepaid Expenses and Other Assets (Parenthetical) (Detail) $ in Millions	1 Months Ended
	Oct. 31, 2015USD ($)
Subsequent Event [Member] | CROs [Member]
Schedule Of Prepaid Expenses And Other Assets [Line Items]
Prepayments to clinical expenses	$ 0.4

Balance Sheet Details - Summa64

Balance Sheet Details - Summary of Property and Equipment (Parenthetical) (Detail) - USD ($)		3 Months Ended			9 Months Ended			12 Months Ended
		Sep. 30, 2015		Jun. 30, 2015	Sep. 30, 2015		Sep. 30, 2014	Dec. 31, 2014		Dec. 31, 2013	Dec. 31, 2012
Property, Plant and Equipment [Line Items]
Property and equipment, accumulated depreciation		$ 287,000	[1],[2]		$ 287,000	[1],[2]		$ 364,000	[1],[2]	$ 247,000
Asset impairment charge					192,000
Property and equipment, net		133,000			133,000			763,000		308,000
Depreciation expense					371,000		$ 110,000	153,000		67,000	$ 64,000
MYDICAR [Member]
Property, Plant and Equipment [Line Items]
Asset impairment charge					200,000
Office Furniture and Other Equipment [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross		170,000	[1]		170,000	[1]		881,000	[1]	$ 555,000
Office Furniture and Other Equipment [Member] | MYDICAR [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross		800,000			800,000
Property and equipment, accumulated depreciation		300,000			300,000
Asset impairment charge				$ 200,000
Property and equipment, net				$ 300,000
Leasehold Improvements [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	[2]	246,000			246,000			$ 246,000
Property and equipment, net		100,000			$ 100,000
Depreciation expense		$ 100,000
Sublease amended termination date					Nov. 13, 2015
Sublease original termination date					2021-09
[1]	Following the CUPID 2 trial results and the decision to not pursue additional previously planned development activities with MYDICAR, the Company sold certain MYDICAR manufacturing assets in the third quarter of 2015. The assets had a historical cost of $0.8 million and accumulated depreciation of $0.3 million. The Company had recognized an impairment charge of $0.2 million in the second quarter of 2015 related to the assets which had reduced the net asset value to $0.3 million, the amount of cash proceeds received (see Note 7).
[2]	In September 2015, in light of the scale-down of certain operations, the Company terminated a sublease agreement effective November 13, 2015, as amended, in order to reduce the Company's office space and corresponding rent obligations. The sublease was originally scheduled to expire in September 2021. The Company revised the estimated depreciable life of the leasehold improvements associated with the facility to end on November 13, 2015. The change in estimated life resulted in an acceleration of depreciation expense in the amount of $0.1 million in the third quarter of 2015. The net book value of the leasehold improvements was $0.1 million at September 30, 2015.

Stockholders' Equity - Addition

Stockholders' Equity - Additional Information (Detail) - USD ($) $ in Millions	1 Months Ended		9 Months Ended	12 Months Ended
	Feb. 28, 2014	Jan. 31, 2014	Sep. 30, 2015	Dec. 31, 2014	Sep. 30, 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock reserved for issuance, description			The number of shares of common stock reserved for issuance will automatically increase on January 1 of each calendar year through January 1, 2023 by the least of (1) 1% of the total number of shares of the Company's common stock outstanding on December 31 of the preceding calendar year, (2) 384,307 shares, or (3) a number determined by the Company's board of directors that is less than (1) and (2).	The number of shares of common stock reserved for issuance will automatically increase on January 1 of each calendar year, from January 1, 2015 through January 1, 2023 by the least of (1) 1% of the total number of shares of the Company's common stock outstanding on December 31 of the preceding calendar year, (2) 384,307 shares, or (3) a number determined by the Company's board of directors that is less than (1) and (2).
Unrecognized compensation cost			$ 7.3	$ 8.9
Unrecognized compensation cost expected to be recognized as expense period			2 years 10 months 24 days	3 years
Common Stock Options [Member] | Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options, expiration Period			10 years	10 years
Common Stock Options [Member] | Minimum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options, vesting period			4 years	4 years
Prior Plans [Member] | Common Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares available for grant			0		0
2013 Equity Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage of common stock outstanding to increase shares reserved for issuance	5.00%
Common stock reserved for issuance, description			Additionally, the 2013 Equity Incentive Plan provides for the grant of performance cash awards. The number of shares of common stock reserved for issuance under the 2013 Equity Incentive Plan will automatically increase on January 1 of each year continuing through and including January 1, 2023 by 5% of the total number of shares of the Company's capital stock outstanding on December 31 of the preceding calendar year, or a lesser number of shares determined by the Company's board of directors.	Additionally, the 2013 Plan provides for the grant of performance cash awards. Initially, the aggregate number of shares of common stock that may be issued pursuant to stock awards under the 2013 Plan is the sum of (1) 1,473,738 shares, plus (2) the number of shares (not to exceed 1,569,905 shares) (i) the 26,294 shares reserved for issuance under the 2012 Plan at the time the 2013 Plan became effective, and (ii) any shares subject to outstanding stock options or other stock awards that were granted under the Prior Plans that are forfeited, terminate, expire or are otherwise not issued. Additionally, the number of shares of common stock reserved for issuance under the 2013 Plan will automatically increase on January 1 of each year, beginning on January 1, 2015 and continuing through and including January 1, 2023, by 5% of the total number of shares of the Company’s capital stock outstanding on December 31 of the preceding calendar year, or a lesser number of shares determined by the Company’s board of directors.
Common stock authorized for issuance	1,473,738
2013 Equity Incentive Plan [Member] | Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock authorized for issuance	1,569,905
2013 Employee Stock Purchase Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage of common stock outstanding to increase shares reserved for issuance	1.00%	1.00%
Common stock authorized for issuance	165,732
2013 Employee Stock Purchase Plan [Member] | Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock authorized for issuance	384,307	384,307

Stockholders' Equity - Summar66

Stockholders' Equity - Summary of Company's Stock Option and RSU Activity (Detail)	9 Months Ended
	Sep. 30, 2015shares
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Options and RSUs, Outstanding at beginning	2,408,634
Options and RSUs, Granted	1,342,750
Options and RSUs, Exercised	(383,011)
Options and RSUs, Cancelled	(1,841,275)
Options and RSUs, Outstanding at ending	1,527,098

Stockholders' Equity - Schedule

Stockholders' Equity - Schedule of Allocation of Stock-based Compensation for Equity Awards (Detail) - USD ($) $ in Thousands		3 Months Ended		9 Months Ended
		Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense		$ (18)	$ 911	$ 3,183	$ 2,178
Research and Development [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	[1]	(663)	391	929	1,175
General and Administrative [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense		$ 645	$ 520	$ 2,254	$ 1,003
[1]	During the three months ended September 30, 2015, following the reduction in workforce initiatives (see Note 7), the Company reversed the previously recorded expense for unvested options of terminated employees aggregating $0.8 million.

Stockholders' Equity - Schedu68

Stockholders' Equity - Schedule of Allocation of Stock-based Compensation for Equity Awards (Parenthetical) (Detail) $ in Millions	3 Months Ended
	Sep. 30, 2015USD ($)
Research and Development [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Reversal amount of stock-based compensation expense	$ 0.8

Restructuring Charges - Additio

Restructuring Charges - Additional Information (Detail) $ in Thousands	3 Months Ended		9 Months Ended
	Dec. 31, 2015USD ($)	Sep. 30, 2015USD ($)Employees	Sep. 30, 2015USD ($)Employees
Restructuring Cost and Reserve [Line Items]
Reduction of current peak employees percentage			70.00%
Current peak workforce | Employees		34	34
Reduction in force, description			In light of the CUPID 2 results and following analysis of the CUPID 2 data, the Company's board of directors, in two phases prior to September 30, 2015, approved an approximately 70% aggregate reduction of the Company's peak workforce of 34 employees to reduce operating expenses and conserve cash resources.
Employee severance and benefit arrangements			$ 2,400
Number of employees impacted | Employees			25
Retention payment accruals			$ 1,100
Facility lease termination costs		$ 1,127	$ 1,127
Restructuring accruals description			The Company recorded the additional accruals as restructuring charges in the consolidated statements of operations. The accrued restructuring balance as of September 30, 2015, is presented as a current liability in the consolidated balance sheets and is expected to be paid within the fourth quarter of 2015.
Asset impairment, net			$ 192
Scenario, Forecast [Member]
Restructuring Cost and Reserve [Line Items]
Retention payment accruals	$ 300
MYDICAR [Member]
Restructuring Cost and Reserve [Line Items]
Asset impairment, net			$ 200

Restructuring Charges - Schedul

Restructuring Charges - Schedule of Restructuring Charges (Detail) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
	Sep. 30, 2015	Sep. 30, 2015
Restructuring and Related Activities [Abstract]
Employee severance and related costs	$ 675	$ 3,543
Facility lease termination costs	1,127	1,127
Asset impairments	(21)	192
Total restructuring and asset impairment charges	$ 1,781	$ 4,862

Restructuring Charges - Sched71

Restructuring Charges - Schedule of Accrued Restructuring Activity (Detail) $ in Thousands	9 Months Ended
	Sep. 30, 2015USD ($)
Restructuring Cost and Reserve [Line Items]
Additional accruals	$ 4,670
Cash payments	(4,061)
Ending balance	609
Employee Severance and Related Costs [Member]
Restructuring Cost and Reserve [Line Items]
Additional accruals	3,543
Cash payments	(2,934)
Ending balance	609
Facility Lease Termination Costs [Member]
Restructuring Cost and Reserve [Line Items]
Additional accruals	1,127
Cash payments	$ (1,127)

Litigation - Additional Informa

Litigation - Additional Information (Detail)	Jul. 31, 2015Complaints
Commitments and Contingencies Disclosure [Abstract]
Number of complaints filed	3