Income Taxes - Significant Components of Deferred Tax Assets (Detail) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Deferred tax assets:
Federal and state net operating loss carry-forwards	$ 156,066	$ 147,408
Federal and state research credit carry-forwards	13,177	12,557
Capitalized research costs	4,824	5,119
Deferred revenue	244	1,221
Stock-based compensation	5,739	5,275
Property and equipment	120	127
Accrued liabilities	207	133
Gross deferred tax assets	180,377	171,840
Valuation allowance	$ (180,377)	$ (171,840)