Long-Lived Assets - Summary of Carrying Value of Assets (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Finite Lived Intangible Assets [Line Items]
Gross Carrying Amount	$ 315,502	$ 306,835
Accumulated Amortization	(236,508)	(219,204)
Net Amount	78,994	87,631
Acquired client contracts
Finite Lived Intangible Assets [Line Items]
Gross Carrying Amount	151,089	148,872
Accumulated Amortization	(100,864)	(93,767)
Net Amount	50,225	55,105
Software
Finite Lived Intangible Assets [Line Items]
Gross Carrying Amount	164,413	157,963
Accumulated Amortization	(135,644)	(125,437)
Net Amount	$ 28,769	$ 32,526