Goodwill and Identifiable Intangible Assets - Schedule of Finite-lived and Indefinite-lived Intangible Assets (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Schedule of Finite-lived and Indefinite-lived Intangible Assets [Line Items]
Accumulated Amortization	$ (383,316)	$ (341,666)
Total	330,679
Gross Carrying Amount, Trade names (unamortized)	209,840	198,739
Accumulated Impairment Charge, Trade names (unamortized)	(52,233)	(52,233)
Total, Trade names (unamortized)	157,607	146,506
Gross Carrying Amount, Total	928,669	893,769
Accumulated Impairment Charge, Total	(57,067)	(57,067)
Total	488,286	495,036
Contract backlog
Schedule of Finite-lived and Indefinite-lived Intangible Assets [Line Items]
Gross Carrying Amount	58,945	55,545
Accumulated Amortization	(56,812)	(55,229)
Accumulated Impairment Charge	0	0
Total	2,133	316
Developed technology/Vendor network
Schedule of Finite-lived and Indefinite-lived Intangible Assets [Line Items]
Gross Carrying Amount	95,661	95,661
Accumulated Amortization	(55,318)	(50,479)
Accumulated Impairment Charge	0	0
Total	40,343	45,182
Customer relationships
Schedule of Finite-lived and Indefinite-lived Intangible Assets [Line Items]
Gross Carrying Amount	522,855	500,756
Accumulated Amortization	(240,073)	(206,319)
Accumulated Impairment Charge	(4,834)	(4,834)
Total	277,948	289,603
Non-competition agreements
Schedule of Finite-lived and Indefinite-lived Intangible Assets [Line Items]
Gross Carrying Amount	10,220	10,220
Accumulated Amortization	(10,220)	(10,178)
Accumulated Impairment Charge	0	0
Total	0	42
Trade names (amortized)
Schedule of Finite-lived and Indefinite-lived Intangible Assets [Line Items]
Gross Carrying Amount	31,148	32,848
Accumulated Amortization	(20,893)	(19,461)
Accumulated Impairment Charge	0	0
Total	$ 10,255	$ 13,387