Partners' Capital And Distributions (Narrative) (Details) (USD $) In Millions, except Share data, unless otherwise specified	3 Months Ended						3 Months Ended				0 Months Ended				3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Dec. 31, 2010	Mar. 31, 2012 Waiver Units Class 1 [Member]	Mar. 31, 2012 Waiver Units Class 2 [Member]	Mar. 31, 2012 Waiver Units Class 3 [Member]	Mar. 31, 2012 Waiver Units Class 4 [Member]	Mar. 28, 2012 Class A [Member]	Mar. 31, 2012 Class A [Member]	Mar. 31, 2012 Class B [Member]	Mar. 31, 2012 Waiver Units [Member]	Mar. 31, 2012 Class One [Member]	Mar. 31, 2012 Class Two [Member]	Mar. 31, 2012 Class Three [Member]	Mar. 31, 2012 Class Four [Member]
Partners Capital And Distributions [Line Items]
Issuance of common units	5,750,000										5,750,000
Price per share of common units issued											$ 30.80
Proceeds received from offering, net of costs											$ 169.5
Common units, outstanding	79,465,000	64,615,000	71,965,000			64,615,000						79,424,522	39,997
Waiver units authorized							1,750,000	1,750,000	1,750,000	1,750,000
Waiver units issued							1,738,000	1,738,000	1,738,000	1,738,000
Conversion feature, minimum distribution coverage ratio															1.1	1.1	1.1	1.1
Conversion feature threshold, quarterly distribution, minimum, per unit															$ 0.43	$ 0.46	$ 0.49	$ 0.52
Distribution paid per common unit	$ 0.4500	$ 0.4075	$ 0.4400	$ 0.4275	$ 0.4150	$ 0.4000								$ 0.44
Waiver units outstanding								5,214,099	5,214,099	5,214,099