Revenue Recognition (Change to Prior Revenue Guidance Related to Classification in The Statements of Income) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Service revenue and sales	$ 444,151	$ 417,444	$ 1,325,140	$ 1,238,367
Cost of services provided and goods sold	305,312	288,047	915,589	859,039
Selling, general and administrative expenses	67,177	$ 66,919	204,474	$ 205,031
ASC 605 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Service revenue and sales	451,325		1,346,949
Cost of services provided and goods sold	307,881		923,452
Selling, general and administrative expenses	71,782		218,420
Adjustment [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Service revenue and sales	(7,174)		(21,809)
Cost of services provided and goods sold	(2,569)		(7,863)
Selling, general and administrative expenses	(4,605)		(13,946)
ASC 606 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Service revenue and sales	444,151		1,325,140
Cost of services provided and goods sold	305,312		915,589
Selling, general and administrative expenses	$ 67,177		$ 204,474