Income Taxes - Narrative (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Taxes [Line Items]
Release from valuation allowance	$ 1,600
Benefit from intraperiod tax allocation	(400)
Change in valuation allowance	59,049	$ 22,516	$ 5,415
Unrecognized tax benefits	6,543	3,427	$ 1,712	$ 884
Federal
Income Taxes [Line Items]
Net operating loss carryforwards	365,300	152,300
Tax credit carryforwards, research	6,800	3,500
State
Income Taxes [Line Items]
Net operating loss carryforwards	223,200	73,200
Tax credit carryforwards, research	$ 5,300	$ 2,900