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 Taxes [Line Items]
Tax at statutory federal rate		34.00%	34.00%	34.00%
Increase in valuation allowance		$ 2,400,000	$ 18,700,000	$ 23,400,000
Unrecognized tax benefits		4,233,000	3,384,000	3,844,000	$ 1,962,000
Accrued interest and penalties		0	$ 0	$ 0
Research and Development Credit Carryforwards [Member] | California state [Member]
Income Taxes [Line Items]
Tax credit carry forwards		5,500,000
Federal [Member]
Income Taxes [Line Items]
Increase in net operating loss carryforwards		18,600,000
Net operating loss carryforward		$ 260,700,000
Net operating loss expiration date		2026
Federal [Member] | Research and Development Credit Carryforwards [Member]
Income Taxes [Line Items]
Tax credit carry forwards		$ 7,700,000
State and Local Jurisdiction [Member]
Income Taxes [Line Items]
Net operating loss carryforward		$ 101,500,000
Net operating loss expiration date		2020
Scenario Forecast [Member]
Income Taxes [Line Items]
Tax at statutory federal rate	21.00%