Schedule of Income Tax Reconciliation (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Income Tax Disclosure [Abstract]
Tax computed at the federal statutory rate	$ (93,839)	$ (81,356)	$ (48,268)
State taxes	(15,693)	(16,620)	(8,465)
Permanent items	6,152	4,225	9,956
R&D credits	(2,728)	(5,029)	(3,697)
Other	(113)	(2,571)	690
Change in valuation allowance	106,221	101,351	49,784
Total provision	$ 0	$ 0	$ 0