Goodwill and Intangible Assets - Summary of Carrying Value of Assets (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Finite Lived Intangible Assets [Line Items]
Gross Carrying Amount	$ 343,997	$ 320,079
Accumulated Amortization	(260,269)	(245,614)
Net Amount	83,728	74,465
Acquired customer contracts
Finite Lived Intangible Assets [Line Items]
Gross Carrying Amount	166,634	153,790
Accumulated Amortization	(111,602)	(105,778)
Net Amount	55,032	48,012
Software
Finite Lived Intangible Assets [Line Items]
Gross Carrying Amount	177,363	166,289
Accumulated Amortization	(148,667)	(139,836)
Net Amount	$ 28,696	$ 26,453