Summary of Significant Accounting Policies - Other Long-lived Assets, Goodwill, and Computer Software Developed or Obtained for Internal Use (Details)	3 Months Ended	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2020 USD ($) asset_grouping	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)
Summary of Significant Accounting Policies [Line Items]
Number of asset groupings | asset_grouping		6
Impairment of long-lived assets, property and equipment		$ 0	$ 0	$ 0
Impairment of long-lived assets, definite-lived intangible assets		0	0	0
Capitalized costs related to software developed or obtained for internal use		$ 4,400,000	$ 6,200,000	$ 2,000,000.0
Customer relationships | Minimum
Summary of Significant Accounting Policies [Line Items]
Intangible assets, useful life		9 years
Customer relationships | Maximum
Summary of Significant Accounting Policies [Line Items]
Intangible assets, useful life		15 years
Non-competition agreements | Minimum
Summary of Significant Accounting Policies [Line Items]
Intangible assets, useful life		1 year
Non-competition agreements | Maximum
Summary of Significant Accounting Policies [Line Items]
Intangible assets, useful life		5 years
Trade names | Minimum
Summary of Significant Accounting Policies [Line Items]
Intangible assets, useful life	1 year	1 year
Trade names | Maximum
Summary of Significant Accounting Policies [Line Items]
Intangible assets, useful life	2 years	2 years
Internally developed and other purchased software | Minimum
Summary of Significant Accounting Policies [Line Items]
Intangible assets, useful life		3 years
Internally developed and other purchased software | Maximum
Summary of Significant Accounting Policies [Line Items]
Intangible assets, useful life		7 years