Income Taxes - Significant Components of Net Deferred Tax Assets (Detail) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Income Tax Disclosure [Abstract]
Net operating loss carry forwards	$ 33,684	$ 32,143
Research and development tax credits	4,982	2,776
Accruals and reserves	4,465	1,693
Depreciation and amortization	42	33
Total deferred tax assets	43,173	36,645
Less: Valuation allowance	$ (43,173)	$ (36,645)