Long-Lived Assets - Summary of Carrying Value of Assets (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Finite Lived Intangible Assets [Line Items]
Gross Carrying Amount	$ 307,171	$ 303,929
Accumulated Amortization	(208,983)	(202,073)
Net Amount	98,188	101,856
Acquired client contracts
Finite Lived Intangible Assets [Line Items]
Gross Carrying Amount	149,348	148,148
Accumulated Amortization	(86,434)	(82,692)
Net Amount	62,914	65,456
Software
Finite Lived Intangible Assets [Line Items]
Gross Carrying Amount	157,823	155,781
Accumulated Amortization	(122,549)	(119,381)
Net Amount	$ 35,274	$ 36,400