Other Intangible Assets, Net (Schedule of Finite-Lived Intangible Assets by Major Class) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Finite-Lived Intangible Assets [Line Items]
Amortization of Intangible Assets	$ 16,300	$ 13,900	$ 31,500	$ 27,900
Gross	889,629		889,629		$ 843,901
Accumulated Amortization	(397,509)		(397,509)		(368,288)
Net	492,120		492,120		475,613
Client lists
Finite-Lived Intangible Assets [Line Items]
Gross	722,255		722,255		690,693
Accumulated Amortization	(325,387)		(325,387)		(303,632)
Net	396,868		396,868		387,061
Non-compete agreements
Finite-Lived Intangible Assets [Line Items]
Gross	33,830		33,830		28,118
Accumulated Amortization	(17,674)		(17,674)		(15,528)
Net	16,156		16,156		12,590
Trade names and licenses
Finite-Lived Intangible Assets [Line Items]
Gross	133,544		133,544		125,090
Accumulated Amortization	(54,448)		(54,448)		(49,128)
Net	$ 79,096		$ 79,096		$ 75,962