Segment Information (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
Segment Total Revenue [Line Items]
Total revenues	$ 2,375,753	$ 2,203,977	$ 4,668,728	$ 4,486,412
US Segment Reporting Information [Member]
Segment Total Revenue [Line Items]
Total revenues	1,370,221	1,255,317	2,694,368	2,608,543
Canada Segment Reporting Information [Member]
Segment Total Revenue [Line Items]
Total revenues	276,239	264,098	551,862	530,625
Europe And South Africa Segment Reporting Information [Member]
Segment Total Revenue [Line Items]
Total revenues	323,943	296,385	632,280	577,388
Asia Pacific Segment Reporting Information [Member]
Segment Total Revenue [Line Items]
Total revenues	377,733	346,474	737,418	685,988
Corporate And Other Segment Reporting Information [Member]
Segment Total Revenue [Line Items]
Total revenues	$ 27,617	$ 41,703	$ 52,800	$ 83,868