Partners' Capital and Distributions (Details) (USD $)	3 Months Ended				6 Months Ended
	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012	Feb. 27, 2013
Issuance of common units and Class F units in connection with SUGS Acquisition	6,274,483			0	6,274,483	0
Sales price per Class F common unit							$ 23.91
Discount per Class F common unit							2.19
Issuance of common units under equity distribution program, net of costs					128,000,000
Distributions per common unit	$ 0.465	$ 0.460	$ 0	$ 0.46	$ 0.925	$ 0.92
Dividends Payable, Date of Record	Aug. 05, 2013	May 06, 2013	Feb. 07, 2013
Dividends Payable, Date to be Paid	Aug. 14, 2013	May 13, 2013	Feb. 14, 2013
Remaining amount available to be issued under the Equity Distribution Agreement	56,000,000				56,000,000
Class F Units [Member]
Issuance of common units under equity distribution program, net of costs					$ 0