Components of Net Deferred Tax Asset (Detail) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Deferred tax assets:
Net operating loss carryforwards	$ 721,588	$ 699,997
Research and development credits	73,646	73,227
Capitalized research	5,872	28,516
Payments from collaboration	52,484	19,217
Milestone Rights	3,242	5,321
Accrued expenses	251	768
Loss on purchase commitment	24,084
Non-qualified stock option expense	16,941	43,691
Capitalized patent costs	8,574	8,624
Other	7,186	131
Depreciation	48,755	3,010
Total net deferred tax assets	962,623	882,502
Valuation allowance	(962,623)	(882,502)
Net deferred tax assets	$ 0	$ 0