Other Intangible Assets, Net (Schedule of Finite-Lived Intangible Assets by Major Class) (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Finite-Lived Intangible Assets [Line Items]
Gross	$ 844,717	$ 843,901
Accumulated Amortization	(382,936)	(368,288)
Net	461,781	475,613
Client lists
Finite-Lived Intangible Assets [Line Items]
Gross	691,647	690,693
Accumulated Amortization	(314,706)	(303,632)
Net	376,941	387,061
Non-compete agreements
Finite-Lived Intangible Assets [Line Items]
Gross	28,113	28,118
Accumulated Amortization	(16,473)	(15,528)
Net	11,640	12,590
Trade names and licenses
Finite-Lived Intangible Assets [Line Items]
Gross	124,957	125,090
Accumulated Amortization	(51,757)	(49,128)
Net	$ 73,200	$ 75,962