Income Taxes - Reconciliation Between Provision for Income Taxes and Income Taxes (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Income Tax Disclosure [Abstract]
Computed “expected” tax benefit	$ (3,152)	$ (5,607)	$ (10,621)
State income taxes, net of federal benefit	0	(444)	(1,947)
Tax effect of:
Change in valuation allowance	(4,069)	5,102	13,074
Rate change	3,524	0	0
Expiration of prior year credits and net operating losses	786	675	(237)
Research and development and other tax credits carryovers	0	0	(672)
Stock compensation	376	274	337
Uncertain tax positions	3,074	0	0
Other	(539)	0	66
Provision for income taxes	$ 0	$ 0	$ 0