Income Taxes - Schedule of Temporary Differences That Give Rise to Significant Net Deferred Tax Assets (Detail) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Deferred tax assets
Net operating losses	$ 182,992	$ 160,333
Capitalized research and development expenses	21,444	30,929
Credit carryforwards	93,113	62,362
Depreciation	2,128	2,579
Deferred compensation	11,664	10,682
Accrued expenses	1,807	12
Deferred revenue	10,999	960
Other temporary differences	17,235	9,195
Total gross deferred tax asset	341,382	277,052
Valuation allowance	(326,577)	(257,489)	$ (207,304)	$ (169,651)
Net deferred tax asset	14,805	19,563
Deferred tax liabilities
Intangible assets	(2,667)	(3,106)
Debt discount	(12,138)	(16,457)
Net deferred taxes	$ 0	$ 0