Components of Net Deferred Tax Assets (Detail) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Components Of Deferred Tax Assets And Liabilities [Line Items]
Operating loss carryforwards	$ 44,219	$ 37,152
Tax credit carryforwards	1,195	1,195
Other temporary differences	5,707	5,048
Deferred Tax Assets, Gross, Total	51,121	43,395
Less valuation allowance	(51,121)	(43,395)
Net deferred tax asset	$ 0	$ 0