Subsequent Events (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	0 Months Ended							12 Months Ended
	May 15, 2012		Feb. 14, 2012	Nov. 14, 2011	Aug. 12, 2011	May 13, 2011	Feb. 14, 2011	Dec. 31, 2012	Dec. 31, 2011
Subsequent Events [Abstract]
Cash distribution per unit	$ 0.8400	[1]	$ 0.8150	$ 0.8000	$ 0.7850	$ 0.7700	$ 0.7575	$ 1.6550	$ 3.1125
Total cash distributions	$ 95,004	[1]	$ 92,177	$ 90,189	$ 88,498	$ 86,807	$ 85,398	$ 187,181	$ 350,892

[1] Our general partner's board of directors declared this cash distribution on April 24, 2012 to be paid on May 15, 2012 to unitholders of record at the close of business on May 8, 2012.