Income Taxes - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Income Tax Contingency [Line Items]
Change in valuation allowance	$ 4,757,000	$ 4,300,000
Unrecognized tax benefits	1,072,000	$ 1,410,000	$ 1,093,000
Accrued interest expense and penalties related to uncertain tax positions	0
Research and Development Credit [Member]
Income Tax Contingency [Line Items]
Unrecognized tax benefits	1,072,000
Domestic Tax Authority [Member]
Income Tax Contingency [Line Items]
Operating loss carry-forwards	$ 241,832,000
Expiry year of operating loss carry-forwards	2020
Tax credits related to federal and state research and development	$ 3,148,000
Expiry year of operating loss carry-forwards related to federal and state research and development activities	2021
California [Member] | State and Local Jurisdiction [Member]
Income Tax Contingency [Line Items]
Operating loss carry-forwards	$ 50,135,000
Expiry year of operating loss carry-forwards	2017
Tax credits related to federal and state research and development	$ 1,139,000