Income Taxes - Effect of Temporary Differences and Carryforwards (Detail) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Income Tax Disclosure [Abstract]
Net operating loss carryforwards	$ 57,158	$ 47,444
Research and development tax credit carryforwards	3,124	2,332
Stock-based compensation	3,212	1,583
Other	7,135	2,564
Total deferred tax assets	70,629	53,923
Less: Valuation allowance	(70,629)	(53,923)	$ (36,012)	$ (25,047)
Net deferred tax assets	$ 0	$ 0