Components of Net Deferred Tax Assets (Detail) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Deferred tax assets:
Net operating loss carryforwards	$ 524,377	$ 507,235
Research and development credits	81,583	83,461
Capitalized research	557	1,016
Milestone Rights	3,521	1,908
Accrued expenses	1,156	211
Loss on purchase commitment	23,194	23,654
Non-qualified stock option expense	2,551	7,004
Capitalized patent costs	5,090	5,194
Other	669	795
Depreciation	22,560	23,820
Deferred Product Revenue & Costs	107	0
Total net deferred tax assets	665,365	654,298
Valuation allowance	(665,365)	(654,298)
Net deferred tax assets	$ 0	$ 0