Partners' Capital and Distributions (Narrative) (Details) (USD $)	3 Months Ended									12 Months Ended	1 Months Ended		12 Months Ended	0 Months Ended		1 Months Ended
	Dec. 31, 2011 days	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2010	Sep. 30, 2010	Jun. 30, 2010	Mar. 31, 2010	Dec. 31, 2009	Dec. 31, 2011 days	Oct. 31, 2011 Common Unit Public Offering [Member]	Aug. 31, 2010 Common Unit Public Offering [Member]	Dec. 31, 2009 Common Unit Public Offering [Member]	May 02, 2011 Private Common Unit Offering [Member]	May 25, 2010 Private Common Unit Offering [Member]	May 31, 2010 Private Common Unit Offering [Member]	Jan. 15, 2008 Class D Common Units [Member]	Dec. 31, 2011 Gathering And Processing [Member]	Dec. 31, 2011 General Partner [Member]
Capital Unit [Line Items]
Distributions per unit	$ 0.46	$ 0.455	$ 0.450	$ 0.445	$ 0.445	$ 0.445	$ 0.445	$ 0.445	$ 0.445
Public common units offerings - (in Units)											11,500,000	17,537,500	12,075,000
Price per common unit issued in public offering											$ 20.92
Proceeds from common unit issuances, net of issuance costs										$ 203,900,000	$ 231,800,000
Partnership sale of units, amount												408,100,000	225,000,000
Private common unit offering														8,500,001	26,266,791
Partnership units issued, value																584,400,000
Noncontrolling interest, ownership percentage by parent																49.90%
Partner contributions																$ 12,300,000
Limited Partners' Capital account, units issued	157,437,608				137,281,336					157,437,608							7,276,506
Noncontrolling interest ownership percentage in joint ventures, by third party																		40.00%
Required distribution of all Partnership's available cash, number of days after each quarter	45									45
General partners interest in initial distribution										2.00%
Current general partners ownership interest	1.80%									1.80%
Partners' Capital Account, Units																			2,804,592
Payment Date	Feb. 13, 2012	Nov. 14, 2011	Aug. 12, 2011	May 13, 2011	Feb. 14, 2011	Nov. 12, 2010	Aug. 13, 2010	May 14, 2010	Feb. 14, 2010