Segment Reporting (Geographic Data) (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
Segment Reporting Information [Line Items]
Revenues	$ 1,363,877	$ 1,404,113	$ 1,446,096	$ 1,366,161	$ 1,318,698	$ 1,377,079	$ 1,348,549	$ 1,245,627	$ 5,580,247	$ 5,289,953	$ 4,952,000
United States [Member]
Segment Reporting Information [Line Items]
Revenues									5,189,792	4,965,630	4,665,728
Canada [Member]
Segment Reporting Information [Line Items]
Revenues									114,451	110,799	106,331
Other Countries [Member]
Segment Reporting Information [Line Items]
Revenues									$ 276,004	$ 213,524	$ 179,941