Income Taxes - Components of Net Deferred Tax Assets (Detail) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Net deferred income tax assets (liability):
Depreciation and amortization	$ 365	$ 322
Accrued expenses and reserves	411	720
Net operating loss carryforwards	20,448	20,135
Research and development credit carryforwards	2,740	2,673
Stock-based compensation	840	750
Other	91
Gross deferred tax assets	24,895	24,600
Less: valuation allowance	(24,911)	(24,552)
Net deferred tax liability	$ (16)
Net deferred tax assets		$ 48