Income Taxes - Deferred Tax Assets (Detail) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Deferred tax assets:
Net operating loss carryforwards	$ 53,218	$ 33,517
Research and development tax credits	4,903	3,269
Stock compensation	2,000	879
Foreign net operating loss carryforwards	333	377
Other, net	1,823	1,715
Total deferred tax assets	62,277	39,757
Less valuation allowance	(62,277)	(39,757)
Deferred Tax Assets, Net of Valuation Allowance, Total	$ 0	$ 0