Summary of Significant Accounting Policies - Property and Equipment and Related Accumulated Depreciation (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2020	Dec. 31, 2019
Property, Plant and Equipment [Line Items]
Gross property, plant and equipment	$ 14,044	$ 14,044
Less accumulated depreciation	(5,223)	(3,664)
Net property and equipment	$ 8,821	10,380
Minimum
Property, Plant and Equipment [Line Items]
Useful life	3 years
Maximum
Property, Plant and Equipment [Line Items]
Useful life	7 years
Computer equipment and software
Property, Plant and Equipment [Line Items]
Useful life	3 years
Gross property, plant and equipment	$ 1,010	1,010
Furniture and fixtures
Property, Plant and Equipment [Line Items]
Gross property, plant and equipment	$ 2,086	2,086
Furniture and fixtures | Minimum
Property, Plant and Equipment [Line Items]
Useful life	5 years
Furniture and fixtures | Maximum
Property, Plant and Equipment [Line Items]
Useful life	7 years
Equipment
Property, Plant and Equipment [Line Items]
Useful life	7 years
Gross property, plant and equipment	$ 2,451	2,451
Leasehold improvements
Property, Plant and Equipment [Line Items]
Gross property, plant and equipment	$ 8,497	$ 8,497
Leasehold improvements | Maximum
Property, Plant and Equipment [Line Items]
Useful life	10 years