Income Taxes - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Income Tax Disclosure [Line Items]
Increase (decrease) in deferred tax valuation allowance		$ (12,600,000)	$ 40,700,000	$ 9,100,000
Iincome tax the federal statutory rate		35.00%	35.00%	35.00%
Decrease related to net federal deferred tax assets		$ 35,600,000
Offsetting change in valuation allowance		35,600,000
Accrued interest and penalties related to unrecognized tax benefits		0	$ 0	$ 0
Tax losst carryforward lost					$ 1,000,000
Tax credit carryforward lost					$ 49,000
Forecast
Income Tax Disclosure [Line Items]
Iincome tax the federal statutory rate	21.00%
Federal Tax Authority [Member]
Income Tax Disclosure [Line Items]
Net operating loss carryforwards		$ 149,400,000
Operating loss carryforward expiration year		2030
Federal Tax Authority [Member] | Research and Development Tax Credit [Member]
Income Tax Disclosure [Line Items]
Tax credit carryforwards		$ 4,400,000
Tax credit carryforward expiration year		2027
State Tax Authority [Member]
Income Tax Disclosure [Line Items]
Operating loss carryforward expiration year		2025
Other net operating losses		$ 1,900,000
State Tax Authority [Member] | California
Income Tax Disclosure [Line Items]
Net operating loss carryforwards		$ 88,300,000
Operating loss carryforward expiration year		2030
State Tax Authority [Member] | Research and Development Tax Credit [Member]
Income Tax Disclosure [Line Items]
Tax credit carryforwards		$ 4,600,000
State Tax Authority [Member] | Minimum Tax Credit Carryforward [Member]
Income Tax Disclosure [Line Items]
Tax credit carryforwards			$ 100,000
Foreign Tax Authority [Member]
Income Tax Disclosure [Line Items]
Foreign tax credit carryforwards		$ 1,200,000
Operating loss carryforward expiration year		2027