Geographic Information (Revenues By Geographic Areas) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Revenues	$ 757,235	$ 802,577	$ 804,890	$ 768,875	$ 697,804	$ 726,742	$ 701,730	$ 640,583	$ 3,133,577	$ 2,766,859	$ 2,269,471
United States [Member]
Revenues									2,798,124	2,474,805	2,067,860
Canada [Member]
Revenues									218,570	198,592	145,078
Other Foreign Countries [Member]
Revenues									$ 116,883	$ 93,462	$ 56,533