Income Taxes - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2007
Income Tax [Line Items]
Gross federal R&D tax credit-related deferred tax assets derecognized	$ 5,600,000
Unrecognized tax benefit	1,539,000	$ 1,314,000	$ 2,570,000
Tax-related penalties or interest recognized	0	$ 0
Federal Income Tax
Income Tax [Line Items]
Net operating loss carryforwards	$ 68,300,000			$ 76,300,000
Net operating loss carry forwards expire period	Dec. 31, 2025
Tax credit carryforwards available to offset future federal tax liabilities	$ 500,000
Tax credit carryforward, expire period	Dec. 31, 2024
Net operating loss carryforward,derecognized				$ 25,900,000
State Income Tax
Income Tax [Line Items]
Net operating loss carryforwards	$ 46,600,000
Net operating loss carry forwards expire period	Dec. 31, 2017
Tax credit carryforwards available to offset future federal tax liabilities	$ 5,600,000
CALIFORNIA
Income Tax [Line Items]
Net operating loss carryforwards	56,100,000
Net operating loss carryforward,derecognized	$ 3,300,000