Amortizable Intangible Assets - Amortizable Intangible Assets (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Finite-Lived Intangible Assets [Line Items]
Gross carrying value	$ 2,200,061	$ 1,959,207
Accumulated amortization	(1,150,401)	(1,042,439)
Net carrying value	1,049,660	916,768
Purchased Customer Accounts
Finite-Lived Intangible Assets [Line Items]
Gross carrying value	2,164,968	1,925,326
Accumulated amortization	(1,118,316)	(1,011,574)
Net carrying value	$ 1,046,652	$ 913,752
Weighted average life in years	15 years	15 years
Non-compete Agreements
Finite-Lived Intangible Assets [Line Items]
Gross carrying value	$ 35,093	$ 33,881
Accumulated amortization	(32,085)	(30,865)
Net carrying value	$ 3,008	$ 3,016
Weighted average life in years	4 years 7 months 6 days	4 years 7 months 6 days