Selected Income Statement Information Selected Income Statement Information (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Revenue:
Services	$ 2,336,304	$ 2,174,739	$ 1,887,957
Products	1,323,320	1,112,280	894,647
Total revenue	3,659,624	3,287,019	2,782,604
Cost of Services and Products:
Services	1,742,411	1,624,483	1,418,511
Products	946,923	788,109	642,199
Unallocated expenses	111,089	108,891	94,036
Total cost of services and products	2,800,423	2,521,483	2,154,746
Gross margin:
Services	593,893	550,256	469,446
Products	376,397	324,171	252,448
Unallocated expenses	(111,089)	(108,891)	(94,036)
Gross Margin	$ 859,201	$ 765,536	$ 627,858