Income Taxes - Components of Deferred Tax Assets (Detail) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Deferred tax assets:
Net operating loss carryforwards $	$ 60,325	$ 56,794
Research and development credits	34,744	28,509
Stock compensation	19,444	16,620
Capitalized research expenses	2,551	3,695
Impairment loss on available for sale securities/capital loss carryforward	679	685
Intangible assets	1,882
Other temporary differences	10,391	5,070
Total gross deferred tax assets	130,016	111,373
Valuation allowance	(121,072)	(100,586)
Net deferred tax assets	8,944	10,787
Deferred tax liabilities:
Convertible Notes	(8,560)	(10,079)
Other temporary differences	(661)	(485)
Total deferred tax liabilities	(9,221)	(10,564)
Net deferred tax assets		223
Short-term deferred tax assets		402
Long-term deferred tax liabilities	(277)	(179)
Net deferred tax assets		$ 223
Deferred tax liabilities	$ (277)