Income Taxes - Additional Information (Details) - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Tax Credit Carryforward [Line Items]
Income tax provision	$ 256,000	$ 633,000	$ 1,537,000
Net loss before income taxes	$ 178,831,000	$ 322,833,000	$ 289,739,000
Effective income tax rate	(0.10%)	(0.20%)	(0.50%)
Valuation allowance	$ 614,958,000	$ 633,591,000
Increase (decrease) in valuation allowance	18,600,000	62,300,000
Uncertain tax positions increase	3,300,000
Unrecognized tax benefits that would impact valuation allowance	34,700,000
Interest and penalties accrued	0	$ 0
Domestic Tax Authority
Tax Credit Carryforward [Line Items]
Operating loss carryforwards	1,900,000,000
Operating loss carryforwards, subject to expiration	1,700,000,000
Operating loss carryforwards, not subject to expiration	224,800,000
Domestic Tax Authority | Research Tax Credit Carryforward
Tax Credit Carryforward [Line Items]
Tax credit carryforwards	23,000,000.0
Domestic Tax Authority | Investment Tax Credit Carryforward
Tax Credit Carryforward [Line Items]
Tax credit carryforwards	6,600,000
State and Local Jurisdiction
Tax Credit Carryforward [Line Items]
Operating loss carryforwards	1,600,000,000
State and Local Jurisdiction | Research Tax Credit Carryforward
Tax Credit Carryforward [Line Items]
Tax credit carryforwards	$ 14,700,000