Long-Lived Assets - Summary of Carrying Value of Other Intangible Assets (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Finite Lived Intangible Assets [Line Items]
Gross Carrying Amount	$ 303,929
Accumulated Amortization	(202,073)
Net Amount	101,856
Balances without Adoption of ASC 606 | ASC 606
Finite Lived Intangible Assets [Line Items]
Gross Carrying Amount		$ 276,627
Accumulated Amortization		(206,095)
Net Amount		70,532
Investments in client contracts | Balances without Adoption of ASC 606 | ASC 606
Finite Lived Intangible Assets [Line Items]
Gross Carrying Amount		26,616
Accumulated Amortization		(9,782)
Net Amount		16,834
Capitalized costs | Balances without Adoption of ASC 606 | ASC 606
Finite Lived Intangible Assets [Line Items]
Gross Carrying Amount		26,811
Accumulated Amortization		(10,039)
Net Amount		16,772
Acquired client contracts
Finite Lived Intangible Assets [Line Items]
Gross Carrying Amount	148,148
Accumulated Amortization	(82,692)	0
Net Amount	65,456
Acquired client contracts | Balances without Adoption of ASC 606 | ASC 606
Finite Lived Intangible Assets [Line Items]
Gross Carrying Amount		87,308
Accumulated Amortization		(77,288)
Net Amount		10,020
Client contracts
Finite Lived Intangible Assets [Line Items]
Accumulated Amortization	0	(97,109)
Net Amount		43,626
Client contracts | Balances without Adoption of ASC 606 | ASC 606
Finite Lived Intangible Assets [Line Items]
Gross Carrying Amount		140,735
Accumulated Amortization		(97,109)
Net Amount	88,733	43,626
Acquired software
Finite Lived Intangible Assets [Line Items]
Gross Carrying Amount	75,156	66,100
Accumulated Amortization	(65,719)	(64,268)
Net Amount	9,437	1,832
Internal use software
Finite Lived Intangible Assets [Line Items]
Gross Carrying Amount	80,625	69,792
Accumulated Amortization	(53,662)	(44,718)
Net Amount	26,963	25,074
Software
Finite Lived Intangible Assets [Line Items]
Gross Carrying Amount	155,781	135,892
Accumulated Amortization	(119,381)	(108,986)
Net Amount	$ 36,400	$ 26,906