Income Taxes - Significant Components of Deferred Tax Assets and Liabilities (Detail) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Deferred tax assets:
Accrued expenses	$ 619	$ 592
Stock options under ASC 718	2,610	2,240
Net operating loss carry forwards	31,649	20,583
Income tax credit carry forwards	19,369	8,109
Property and equipment	20	12
Intangibles	895	1,793
Other	69	33
Total deferred tax assets	55,231	33,362
Less: valuation allowance	(55,231)	(33,362)
Deferred tax liabilities:
Acquired intangibles	(3,404)	(3,404)
Total deferred tax assets/liabilities, net of valuation allowance	$ (3,404)	$ (3,404)