Income Taxes - Tax Effects of Temporary Differences and Carry Forwards on Deferred Tax Assets (Detail) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Components of Deferred Tax Assets [Abstract]
Net operating loss carry forwards	$ 228,637	$ 187,169
Capitalized start-up costs	7,093	7,475
Research and development credits	8,922	6,320
Stock compensation	10,256	12,683
Other	4,313	6,875
Total deferred tax assets	259,221	220,522
Valuation allowance	(255,765)	(216,220)
Deferred tax liability—fixed assets	(3,456)	(3,056)
Deferred tax liability—derivative liability	0	(1,246)
Net deferred tax assets, after valuation allowance	$ 0	$ 0