Preferred Stock and Stockholders' Equity - Common Stock Warrants Narrative (Detail) (USD $) In Thousands, except Share data, unless otherwise specified	0 Months Ended		1 Months Ended		12 Months Ended
	Jul. 27, 2012	Jul. 18, 2011	Dec. 31, 2014	Jun. 30, 2011	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Schedule Of Common Stock [Line Items]
Shares of common stock exercisable through warrants	15,784,200
Warrants exercise price (in usd per share)	$ 2.50
Warrants expiry date	July 27, 2017
Term of common stock warrant exercisable	5 years	10 years
Fair value of warrant liabilities			$ 4,978		4,978	30,849
Warrant exercisable to Healthcare Royalty, shares		225,000
Investment Warrants, Exercise Price		$ 9.00
Imputed interest on working capital advance			5,297		5,297
Healthcare Royalty Financing Agreement [Member]
Schedule Of Common Stock [Line Items]
Fair value of warrant liabilities			114		114	492
Oxford/SVB [Member]
Schedule Of Common Stock [Line Items]
Shares of common stock exercisable through warrants			508,476	26,455
Warrants exercise price (in usd per share)			$ 1.18	$ 3.78	1.18
Term of common stock warrant exercisable			10 years	7 years
Imputed interest on working capital advance			$ 558		558		$ 76
Warrant [Member]
Schedule Of Common Stock [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Non-Option Equity Instruments, Exercised					465,250	103,500