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Segment Information (Details 2) (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
Revenue $ 294,648 $ 267,405 $ 273,506 $ 235,152 $ 254,068 $ 235,706 $ 236,959 $ 213,670 $ 1,070,711 $ 940,403 $ 688,826
United States [Member]
                     
Revenue                 868,313 755,286 573,723
Canada [Member]
                     
Revenue                 149,807 152,374 97,452
Other Geographical Location [Member]
                     
Revenue                 $ 52,591 $ 32,743 $ 17,651