Provision for Income Taxes on Earnings Subject to Income Taxes Differs from Statutory Federal Rate (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Income Tax Disclosure [Abstract]
Federal income taxes at 35%	$ (31,126)	$ (21,190)	$ (16,131)
State income tax, net of Federal benefit	2	(3,410)	(2,611)
Tax effect on non-deductible expenses	172	10	7
Share-based compensation expense	201	91	215
Change in tax rate	10,773	0	0
Expired tax attributes	5,594	315	151
Research credits	(6,638)	(1,882)	(3,458)
Change in valuation allowance	15,029	25,366	20,504
Uncertain tax positions	5,940	621	1,283
Other	53	79	40
Income Tax Expense (Benefit), Total	$ 0	$ 0	$ 0