Income Taxes - Components of Company's Net Deferred Tax Assets (Detail) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Deferred tax assets:
Net operating loss	$ 39,375	$ 33,485
Capitalized research and development	13,998	6,045
Research and development tax credit	2,413	1,345
Depreciation and amortization	646	819
Stock-based compensation	2,250	489
Accrued expenses	155	440
Total deferred tax assets	58,837	42,623
Deferred tax liabilities:
Beneficial conversion feature		(13)
Net deferred tax asset	58,837	42,610
Less: valuation allowance	(58,837)	(42,610)
Net deferred tax assets	$ 0	$ 0