Segment Reporting (Geographic Data) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2010	Sep. 30, 2010	Jun. 30, 2010	Mar. 31, 2010	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Segment Reporting Information [Line Items]
Revenues	$ 1,318,698	$ 1,377,079	$ 1,348,549	$ 1,245,627	$ 1,213,643	$ 1,270,183	$ 1,306,263	$ 1,161,911	$ 5,289,953	$ 4,952,000	$ 4,269,239
United States [Member]
Segment Reporting Information [Line Items]
Revenues									4,965,630	4,665,728	4,018,870
Canada [Member]
Segment Reporting Information [Line Items]
Revenues									110,799	106,331	81,351
Other [Member]
Segment Reporting Information [Line Items]
Revenues									$ 213,524	$ 179,941	$ 169,018