Segment Reporting (Details 2) (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
Revenue:
Revenues	$ 1,541,094	$ 1,570,720	$ 1,513,344	$ 1,425,376	$ 1,313,426	$ 1,316,948	$ 1,286,123	$ 1,219,938	$ 6,050,534	$ 5,136,435	$ 4,887,254
Long-lived assets
Total	5,673,851				4,808,061				5,673,851	4,808,061	4,722,569
United States [Member]
Revenue:
Revenues									5,075,432	4,313,483	4,126,973
Long-lived assets
Total	4,708,086				4,098,735				4,708,086	4,098,735	3,985,166
Foreign [Member]
Revenue:
Revenues									975,102	822,952	760,281
Long-lived assets
Total	965,765				709,326				965,765	709,326	737,403
Canada [Member]
Revenue:
Revenues									481,593	466,405	424,148
Long-lived assets
Total	481,139				468,062				481,139	468,062	478,091
Europe [Member]
Revenue:
Revenues									324,214	219,508	223,879
Long-lived assets
Total	463,848				219,178				463,848	219,178	232,320
Mexico [Member]
Revenue:
Revenues									147,464	122,312	97,649
Long-lived assets
Total	19,931				21,194				19,931	21,194	16,832
South America [Member]
Long-lived assets
Total	0								0		531
Asia [Member]
Revenue:
Revenues									21,831	14,727	14,605
Long-lived assets
Total	$ 847				$ 892				$ 847	$ 892	$ 9,629