Amortizable Intangible Assets - Amortizable Intangible Assets (Details) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2020	Dec. 31, 2019
Finite-Lived Intangible Assets [Line Items]
Gross carrying value	$ 2,099,793	$ 1,959,207
Accumulated amortization	(1,122,591)	(1,042,439)
Net carrying value	977,202	916,768
Purchased Customer Accounts
Finite-Lived Intangible Assets [Line Items]
Gross carrying value	2,064,938	1,925,326
Accumulated amortization	(1,090,819)	(1,011,574)
Net carrying value	$ 974,119	$ 913,752
Weighted average life (years)	15 years	15 years
Non-compete Agreements
Finite-Lived Intangible Assets [Line Items]
Gross carrying value	$ 34,855	$ 33,881
Accumulated amortization	(31,772)	(30,865)
Net carrying value	$ 3,083	$ 3,016
Weighted average life (years)	4 years 7 months 6 days	4 years 7 months 6 days