Long-Lived Assets - Summary of Carrying Value of Assets (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Investments in client contracts
Finite Lived Intangible Assets [Line Items]
Gross Carrying Amount	$ 26,616	$ 37,482
Accumulated Amortization	(9,782)	(23,265)
Net Amount	16,834	14,217
Capitalized costs
Finite Lived Intangible Assets [Line Items]
Gross Carrying Amount	26,811	16,831
Accumulated Amortization	(10,039)	(5,130)
Net Amount	16,772	11,701
Acquired client contracts
Finite Lived Intangible Assets [Line Items]
Gross Carrying Amount	87,308	83,085
Accumulated Amortization	(77,288)	(68,328)
Net Amount	10,020	14,757
Client contracts
Finite Lived Intangible Assets [Line Items]
Gross Carrying Amount	140,735	137,398
Accumulated Amortization	(97,109)	(96,723)
Net Amount	43,626	40,675
Acquired software
Finite Lived Intangible Assets [Line Items]
Gross Carrying Amount	66,100	65,500
Accumulated Amortization	(64,268)	(62,306)
Net Amount	1,832	3,194
Internal use software
Finite Lived Intangible Assets [Line Items]
Gross Carrying Amount	69,792	64,243
Accumulated Amortization	(44,718)	(37,010)
Net Amount	25,074	27,233
Software
Finite Lived Intangible Assets [Line Items]
Gross Carrying Amount	135,892	129,743
Accumulated Amortization	(108,986)	(99,316)
Net Amount	$ 26,906	$ 30,427