Income Taxes - Schedule of Company's Deferred Tax Assets (Detail) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Deferred tax assets:
Net operating loss carryforwards	$ 114,222	$ 93,824
Research and development tax credit carryforwards	12,518	9,979
Stock-based compensation	8,565	6,853
Deferred revenue	2,918	4,479
Other	3,492	2,807
Total deferred tax asset	141,715	117,942
Valuation allowance	$ 141,715	$ 117,942