Income Taxes - Narrative (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Tax Credit Carryforward [Line Items]
Valuation allowance		$ 55,428	$ 31,617
Increase in valuation allowance		23,800
Unrecognized tax benefits		3,336	1,846	$ 1,201
Research and development tax credits
Tax Credit Carryforward [Line Items]
Unrecognized tax benefits		3,100	1,100
Federal
Tax Credit Carryforward [Line Items]
Operating loss carryforwards		209,500	119,700
Operating loss carryforwards, not subject to expiration		117,700
State
Tax Credit Carryforward [Line Items]
Operating loss carryforwards		$ 143,800	92,300
ASU 2016-09 | Restatement adjustment
Tax Credit Carryforward [Line Items]
Increase in valuation allowance	$ 200
Operating loss carryforwards			$ 200