Stockholders' Equity (Deficit) - Reconciliation of Warrant Liability Measured at Fair Value (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Equity [Abstract]
Beginning Balance	$ 3,961	$ 23,421	$ 32,558
Initial fair value of common stock warrant related to February 2015 offering	14,693
Exercise of warrants	(17)	(10,116)	(11,462)
Change in common stock warrant value	(16,773)	(9,344)	2,325
Ending Balance	$ 1,864	$ 3,961	$ 23,421