Equity and Distributions, Distributions (Details) (USD $)	12 Months Ended		3 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2012 Cash Distribution [Member]	Sep. 30, 2012 Cash Distribution [Member]	Jun. 30, 2012 Cash Distribution [Member]	Mar. 31, 2012 Cash Distribution [Member]	Dec. 31, 2011 Cash Distribution [Member]	Sep. 30, 2011 Cash Distribution [Member]	Jun. 30, 2011 Cash Distribution [Member]	Mar. 31, 2011 Cash Distribution [Member]
Distributions to Partners [Abstract]
Distribution Per Common Unit (in dollars per unit)			$ 0.6600	$ 0.6500	$ 0.6350	$ 0.6275	$ 0.6200	$ 0.6125	$ 0.6050	$ 0.5975
Record Date			Jan. 31, 2013	Oct. 31, 2012	Jul. 31, 2012	Apr. 30, 2012	Jan. 31, 2012	Oct. 31, 2011	Jul. 29, 2011	Apr. 29, 2011
Payment Date			Feb. 07, 2013	Nov. 08, 2012	Aug. 08, 2012	May 09, 2012	Feb. 09, 2012	Nov. 09, 2011	Aug. 10, 2011	May 06, 2011
Number of Designated Units (in units)	26,130,000	30,610,000
Number of Designated Units to be excluded from distributions during 2013	23,700,000
Number of Designated Units to be excluded from distributions during 2014	22,560,000
Number of Designated Units to be excluded from distributions during 2015	17,690,000