Income Taxes - Components of Deferred Tax Assets (Detail) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Deferred tax assets:
Net operating loss carryforwards	$ 46,749	$ 33,267
Research and development credit carryforwards	2,462	1,979
Accruals and other	1,385	948
Capitalized license and organization costs	66	73
Capitalized start-up costs	278	309
Depreciation	21	0
Total gross deferred tax asset	50,961	36,576
Deferred tax liability	0	(18)
Valuation allowance	(50,961)	(36,558)
Net deferred tax asset	$ 0	$ 0