Components of U.S. Deferred Tax Assets and (liabilities) (Detail) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Deferred tax assets:
Federal and state net operating loss carryforwards	$ 207,898	$ 146,725
Federal and state research tax credit carryforwards	18,744	15,337
Deferred revenue	9,192	12,523
Stock options	10,197	3,776
Capitalized acquisition costs	974	1,322
Other	3,942	3,589
Net deferred tax assets before valuation allowance	250,947	183,272
Valuation allowance	$ (250,947)	$ (183,272)