Income Taxes - Components of Net Deferred Tax Assets (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Net deferred income tax assets:
Depreciation and amortization	$ 775	$ 917
Accrued expenses and reserves	2,968	1,771
Net operating loss carryforwards	20,652	20,509
Capital loss carryforwards	290	290
Research and development credit carryforwards	2,673	2,535
Stock-based compensation	487	425
Gross deferred tax assets	27,845	26,447
Less: valuation allowance	(27,673)	(24,102)
Net deferred tax assets	$ 172	$ 2,345