Income Taxes - Additional Information (Detail) - USD ($)	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015
Income Tax [Line Items]
Income tax benefit	$ 0	$ 0	$ 0	$ 0	$ 0	$ 0	$ 0	$ 0	$ 0	$ 0
Increase (decrease) in valuation allowance on deferred tax assets									16,160,000	8,223,000
California research and development tax credit carryforwards	6,509,000				$ 6,509,000				6,509,000	$ 6,509,000
Unrecognized tax benefits	0								0
Interest and penalties accrued on unrecognized tax benefits	0								0
General Business Tax Credit Carryforward [Member]
Income Tax [Line Items]
Tax credit carryforward, amount	18,600,000								18,600,000
Domestic Tax Authority [Member]
Income Tax [Line Items]
Federal net operating loss carryforwards	63,800,000								$ 63,800,000
Net operating loss carryforwards expiration period									2028 through 2036
California [Member]
Income Tax [Line Items]
Net operating loss carryforwards expiration period									2017 through 2036
Net operating loss carryforwards	44,100,000								$ 44,100,000
State and Local Jurisdiction [Member] | Research Tax Credit Carryforward [Member]
Income Tax [Line Items]
California research and development tax credit carryforwards	$ 9,900,000								$ 9,900,000