Income Taxes - Schedule of Significant Components of Company's Deferred Tax Assets (Detail) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Income Tax Disclosure [Abstract]
Net operating loss carryforwards	$ 36,217	$ 27,094
Federal and state tax credits	4,315	3,508
Accelerated depreciation	1,206	1,018
Deferred revenue		566
Stock-based compensation expense	1,106	333
Other	189	197
Gross deferred tax asset	43,033	32,716
Valuation allowance	(43,033)	(32,716)
Net deferred tax asset	$ 0	$ 0