Income Taxes - Tax Effects of Temporary Differences and Carry Forwards on Deferred Tax Assets (Detail) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Income Tax Disclosure [Abstract]
Net operating loss carry forwards	$ 187,169	$ 140,185
Capitalized start-up costs	7,475	8,051
Research and development credits	6,320	5,603
Stock compensation	12,683	10,630
Other	6,875	6,634
Total deferred tax assets	220,522	171,103
Valuation allowance	(216,220)	(166,180)
Deferred tax liability - fixed assets	(3,056)	(3,346)
Deferred tax liability—derivative liability	(1,246)	(1,577)
Net deferred tax assets, after valuation allowance	$ 0	$ 0