Significant Components of Deferred Tax Assets and Liabilities (Detail) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Deferred tax assets:
Net operating loss carryforwards	$ 165,813	$ 151,100
Research and development credit carryforwards	35,131	33,800
Capitalized research and development	17,916	15,500
Deferred compensation	5,908	5,800
Capital loss carryforwards		3,700
Other	3,911	3,200
Total deferred tax assets	228,679	213,100
Valuation allowance	(224,854)	(213,100)
Net deferred tax assets	3,825
Deferred tax liabilities:
Unrealized gain on investments	3,825
Amortization of goodwill	122	115
Total deferred tax liabilities	$ 3,947	$ 115