Income Taxes - Schedule of Net Deferred Tax Assets (Detail) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Deferred tax assets:
Net operating loss carryforwards	$ 25,293	$ 7,946
Research and development tax credit carryforwards	4,180	1,055
Capitalized organization costs	527	571
Stock-based compensation expense	1,897	436
Charitable Contributions	5
Accrued expenses	977	447
Capitalized research and development expenses	126	136
Total deferred tax assets	33,005	10,591
Deferred tax liabilities:
Depreciation and amortization	(228)	(69)
Total deferred tax liabilities	(228)	(69)
Valuation allowance	(32,777)	(10,522)	$ (4,294)	$ (1,599)
Net deferred tax assets	$ 0	$ 0