Consolidated Statements of Convertible Preferred Stock and Stockholders' Deficit (USD $)	Convertible Preferred Stock [Member]	Common Stock [Member]	Additional Paid-in Capital [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Retained Earnings [Member]	Total
Balances at Dec. 31, 2011	$ 83,178,000	$ 2,000	$ 2,412,000	$ (1,000)	$ (74,758,000)	$ (72,345,000)
Balances (in shares) at Dec. 31, 2011	10,657,030	1,986,431
Issuance of Series E convertible preferred stock, net of issuance costs of $1,404	18,845,000
Issuance of Series E convertible preferred stock, net of issuance costs of $1,404 (in shares)	1,672,300
Issuance of common stock upon exercise of options and vesting of stock awards			84,000			84,000
Issuance of common stock upon exercise of options and vesting of stock awards (in shares)		200,264
Stock-based compensation expense			821,000			821,000
Comprehensive loss				5,000	(23,509,000)	(23,504,000)
Balances at Dec. 31, 2012	102,023,000	2,000	3,317,000	4,000	(98,267,000)	(94,944,000)
Balances (in shares) at Dec. 31, 2012	12,329,330	2,186,695
Conversion of preferred stock to common stock	(102,023,000)	13,000	102,010,000			102,023,000
Conversion of preferred stock to common stock (in shares)	(12,329,330)	13,211,120
Reclassification of preferred stock warrants liability to additional paid-in capital			157,000			157,000
Issuance of common stock upon initial public offering, net of issuance costs		9,000	61,477,000			61,486,000
Issuance of common stock upon initial public offering, net of issuance costs (in shares)		8,750,000
Issuance of common stock upon equity offering, net of issuance costs		9,000	32,020,000			32,029,000
Issuance of common stock upon equity offering, net of issuance costs (in shares)		8,625,000
Issuance of common stock upon exercise of options and vesting of stock awards			164,000			164,000
Issuance of common stock upon exercise of options and vesting of stock awards (in shares)		158,277
Stock-based compensation expense			1,440,000			1,440,000
Issuance of warrants in connection with credit facility			130,000			130,000
Comprehensive loss				(1,000)	(41,948,000)	(41,949,000)
Balances at Dec. 31, 2013		33,000	200,715,000	3,000	(140,215,000)	60,536,000
Balances (in shares) at Dec. 31, 2013		32,931,092
Reclassification of preferred stock warrants liability to additional paid-in capital						157,000
Issuance of common stock upon exercise of options and vesting of stock awards			73,000			73,000
Issuance of common stock upon exercise of options and vesting of stock awards (in shares)		61,086
Stock-based compensation expense			2,013,000			2,013,000
Comprehensive loss				(11,000)	(37,998,000)	(38,009,000)
Balances at Dec. 31, 2014		$ 33,000	$ 202,801,000	$ (8,000)	$ (178,213,000)	$ 24,613,000
Balances (in shares) at Dec. 31, 2014		32,992,178