Income Taxes - Additional Information (Details) - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Income Taxes [Line Items]
Current income tax provision	$ 0	$ 0	$ 0
Deferred income tax expense (benefit)	0	(774,000)	$ 1,099,000
Deferred tax assets, operating loss carryforwards, federal	378,800,000
Deferred tax assets, operating loss carryforwards, state and local	446,800,000
Deferred tax assets, tax credit carryforwards, research	8,872,000	$ 7,499,000
Domestic Tax Authority
Income Taxes [Line Items]
Deferred tax assets, operating loss carryforwards, not subject to expiration	264,100,000
Deferred tax assets, operating loss carryforwards, subject to expiration	$ 114,700,000
Operating loss carry forwards expiration period	2027
Deferred tax assets, tax credit carryforwards, research	$ 8,500,000
Domestic Tax Authority | Research Tax Credit Carryforward
Income Taxes [Line Items]
Operating loss carry forwards expiration period	2028
State and Local Jurisdiction
Income Taxes [Line Items]
Deferred tax assets, operating loss carryforwards, not subject to expiration	$ 700,000
Deferred tax assets, operating loss carryforwards, subject to expiration	$ 446,100,000
Operating loss carry forwards expiration period	2031
California Franchise Tax Board
Income Taxes [Line Items]
Deferred tax assets, tax credit carryforwards, research	$ 3,600,000