Income Taxes - Summary of Provision for Income Taxes Reconciles to Amount Computed by Applying Statutory Federal Income Tax Rate (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Income Tax Disclosure [Abstract]
Federal tax benefit, at statutory rate	$ (17,718)	$ (13,447)	$ (14,732)
State benefit, net of federal benefit	(280)	(1,054)	(922)
Foreign tax rate difference	222	0	0
Change in valuation allowance	15,389	11,316	15,577
Change in fair value of warrant	0	1,203	0
Beneficial conversion feature	0	163	0
Research and development credits	(796)	3	(1,084)
Share-based compensation	752	2,402	2,433
Uncertain tax positions	0	(62)	(307)
Change in state apportionment	2,561	(347)	(767)
Other	51	(53)	(115)
Provision for income taxes	$ 181	$ 124	$ 83