Components of U.S. Deferred Tax Assets and (liabilities) (Detail) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Deferred tax assets:
Federal and state net operating loss carryforwards	$ 235,015	$ 207,898
Federal and state research tax credit carryforwards	17,927	18,744
Federal Orphan Drug Credit	60,822
Deferred revenue	15,566	9,192
Stock options	18,734	10,197
Capitalized acquisition costs	819	974
Other	16,298	3,942
Net deferred tax assets before valuation allowance	365,181	250,947
Valuation allowance	$ (365,181)	$ (250,947)