Summary of Significant Accounting Policies - Impairments (Details) - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Property, Plant and Equipment [Line Items]
Impairment of goodwill	$ 0	$ 0	$ 0
Impairment of leasehold improvements and property and equipment	0	0	$ 0
Impairments of ROU assets	$ 3,400,000	$ 0
Minimum [Member]
Property, Plant and Equipment [Line Items]
Length of time for properties more likely than not of being disposed	12 months
Maximum [Member]
Property, Plant and Equipment [Line Items]
Length of time for properties more likely than not of being disposed	24 months