Income Taxes - Deferred Income Tax (Detail) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Deferred Tax Assets, Net [Abstract]
Net operating loss carryforwards	$ 75,036	$ 60,979
Research and development tax credits	2,131	1,731
Reserves and accruals	1,791	966
Other	4,594	2,433
Total deferred tax assets	83,552	66,109
Valuation allowance	$ (83,552)	$ (66,109)