Income Taxes - Schedule of Effective Income Tax Rate Reconciliation (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Income Tax Disclosure [Abstract]
Computed statutory income tax benefit	$ (29,144)	$ (13,909)	$ (27,837)
Increase in income tax benefit resulting from State income tax benefit, net of federal income taxes	(3,544)	(1,834)	(3,711)
Nondeductible stock based compensation	1,386	575	333
Contribution of services by shareholder	677	527	527
Gain in previously held equity investment	0	(2,477)	0
Research and development tax credits	258	(1,203)	0
Other, net	1,503	1,317	(238)
Income tax reconciliation income tax benefit before valuation allowance, total	(28,864)	(17,004)	(30,926)
Change in valuation allowance for deferred tax assets	28,761	17,004	30,926
Total income tax provision	$ (103)	$ 0	$ 0