Other Identifiable Intangible Assets, Net (Components of Intangible Assets) (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Finite-Lived Intangible Assets [Line Items]
Gross	$ 843,901	$ 786,245
Accumulated Amortization	(368,288)	(307,332)
Finite-Lived Intangible Assets, Net	475,613	478,913
Client lists
Finite-Lived Intangible Assets [Line Items]
Gross	690,693	637,053
Accumulated Amortization	(303,632)	(257,787)
Finite-Lived Intangible Assets, Net	387,061	379,266
Non-compete agreements
Finite-Lived Intangible Assets [Line Items]
Gross	28,118	28,106
Accumulated Amortization	(15,528)	(11,136)
Finite-Lived Intangible Assets, Net	12,590	16,970
Trade names and licenses
Finite-Lived Intangible Assets [Line Items]
Gross	125,090	121,086
Accumulated Amortization	(49,128)	(38,409)
Finite-Lived Intangible Assets, Net	$ 75,962	$ 82,677