Segment Information (Details 3) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Revenues:
Total revenues	$ 1,025,231	$ 942,364	$ 844,761
Long-lived assets:
Total long-lived assets	229,714	204,864	180,709
United States [Member]
Revenues:
Total revenues	700,414	660,998	590,163
Long-lived assets:
Total long-lived assets	141,727	145,217	117,751
Canada [Member]
Revenues:
Total revenues	151,070	140,374	136,066
Long-lived assets:
Total long-lived assets	76,067	47,624	51,182
United Kingdom [Member]
Revenues:
Total revenues	153,027	124,208	93,092
Long-lived assets:
Total long-lived assets	9,757	8,165	8,295
Other International [Member]
Revenues:
Total revenues	20,720	16,784	25,440
Long-lived assets:
Total long-lived assets	$ 2,163	$ 3,858	$ 3,481