Significant Accounting Policies - Property and Equipment (Details) - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Property, Plant and Equipment [Line Items]
Impairment loss	$ 0
Depreciation and amortization	51,800,000	$ 49,500,000	$ 31,400,000
Computer software | Capella Merger
Property, Plant and Equipment [Line Items]
Depreciation	$ 6,900,000	$ 6,300,000	$ 2,600,000
Minimum
Property, Plant and Equipment [Line Items]
Estimated useful life of property and equipment	3 years
Minimum | Computer software
Property, Plant and Equipment [Line Items]
Estimated useful life of property and equipment	3 years
Maximum
Property, Plant and Equipment [Line Items]
Estimated useful life of property and equipment	40 years
Maximum | Computer software
Property, Plant and Equipment [Line Items]
Estimated useful life of property and equipment	10 years