Reporting Segments Schedule of revenues by geographic area (Details) (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
Segment Reporting Information [Line Items]
Total revenue	$ 270,543	$ 279,390	$ 274,398	$ 280,627	$ 267,954	$ 272,474	$ 262,739	$ 256,636	$ 1,104,958	$ 1,059,803	$ 926,289
US
Segment Reporting Information [Line Items]
Total revenue									869,679	889,671	785,227
Canada
Segment Reporting Information [Line Items]
Total revenue									144,089	99,541	68,753
UK
Segment Reporting Information [Line Items]
Total revenue									59,967	55,900	62,467
Other
Segment Reporting Information [Line Items]
Total revenue									$ 31,223	$ 14,691	$ 9,842