Income Taxes - Components of Net Deferred Tax Assets and Liabilities (Detail) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Net Operating Loss	$ 55,521	$ 57,541
Tax Credits	2,034	1,723
Stock Based Compensation	997	1,502
Fixed Assets	(749)	(1,386)
Intangibles	843	1,059
Other	337	1,549
Net deferred tax assets	58,983	61,988
Federal	(58,983)	(61,988)
Deferred tax asset	$ 0	$ 0