Income Taxes - Summary of Provision (Benefit) for Income Taxes Reconciles to Amount Computed by Applying Statutory Federal Income Tax Rate (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Income Tax Disclosure [Abstract]
Federal tax benefit, at statutory rate	$ (13,447)	$ (14,732)	$ (30,142)
State benefit, net of federal benefit	(1,054)	(922)	(757)
Change in valuation allowance	11,316	15,577	27,486
Change in fair value of warrant	1,203	0	0
Beneficial conversion feature	163	0	0
Research and development credits	3	(1,084)	(856)
Share-based compensation	2,402	2,433	1,616
Uncertain tax positions	(62)	(307)	(46)
Goodwill impairment	0	0	3,700
Change in state apportionment	(347)	(767)	0
Other	(53)	(115)	(390)
Provision or income taxes	$ 124	$ 83	$ 611