Fair Value Measurements (Fair Value Of Assets And Liabilities Measured And Recorded On Recurring Basis) (Details) (USD $) In Thousands	Sep. 30, 2011	Dec. 31, 2010
Marketable securities, Assets	$ 3,151	$ 2,032
Fair Value, Measurements, Recurring [Member]
Marketable securities, Assets	3,151	2,032
Interest rate derivatives, Assets	30,564	20,790
Total commodity derivatives, Assets	181,143	93,092
Total Assets	214,858	115,914
Interest rate derivatives, Liabilities	(98,580)	(18,338)
Total commodity derivatives, Liabilities	(143,025)	(65,615)
Total Liabilities	241,605	83,953
Fair Value, Measurements, Recurring [Member] | Fair Value Measurements, Quoted Prices In Active Markets For Identical Assets And Liabilities (Level 1) [Member]
Marketable securities, Assets	3,151	2,032
Interest rate derivatives, Assets	0	0
Total commodity derivatives, Assets	146,078	59,792
Total Assets	149,229	61,824
Interest rate derivatives, Liabilities	0	0
Total commodity derivatives, Liabilities	(119,039)	(62,717)
Total Liabilities	119,039	62,717
Fair Value, Measurements, Recurring [Member] | Fair Value Measurements, Quoted Prices In Active Markets For Identical Assets And Liabilities (Level 1) [Member] | Basis Swaps IFERC/NYMEX [Member]
Total commodity derivatives, Assets	74,892	15,756
Total commodity derivatives, Liabilities	(68,918)	(17,372)
Fair Value, Measurements, Recurring [Member] | Fair Value Measurements, Quoted Prices In Active Markets For Identical Assets And Liabilities (Level 1) [Member] | Swing Swaps IFERC [Member]
Total commodity derivatives, Assets	1,074	1,562
Total commodity derivatives, Liabilities	(1,988)	(3,520)
Fair Value, Measurements, Recurring [Member] | Fair Value Measurements, Quoted Prices In Active Markets For Identical Assets And Liabilities (Level 1) [Member] | Fixed Swaps/Futures [Member]
Total commodity derivatives, Assets	70,112	42,474
Total commodity derivatives, Liabilities	(48,133)	(41,825)
Fair Value, Measurements, Recurring [Member] | Fair Value Measurements, Quoted Prices In Active Markets For Identical Assets And Liabilities (Level 1) [Member] | Forward Physical Swaps [Member]
Total commodity derivatives, Assets	0
Total commodity derivatives, Liabilities	0
Fair Value, Measurements, Recurring [Member] | Fair Value Measurements, Quoted Prices In Active Markets For Identical Assets And Liabilities (Level 1) [Member] | Propane - Forwards/Swaps [Member]
Total commodity derivatives, Assets	0	0
Total commodity derivatives, Liabilities	0
Fair Value, Measurements, Recurring [Member] | Fair Value Measurements, Quoted Prices In Active Markets For Identical Assets And Liabilities (Level 1) [Member] | Options - Puts [Member]
Total commodity derivatives, Assets	0	0
Total commodity derivatives, Liabilities	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value Measurements, Quoted Prices In Active Markets For Identical Assets And Liabilities (Level 1) [Member] | Options - Calls [Member]
Total commodity derivatives, Assets		0
Total commodity derivatives, Liabilities	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value Measurements, Significant Observable Inputs (Level 2) [Member]
Marketable securities, Assets	0	0
Interest rate derivatives, Assets	30,564	20,790
Total commodity derivatives, Assets	35,065	33,300
Total Assets	65,629	54,090
Interest rate derivatives, Liabilities	(98,580)	(18,338)
Total commodity derivatives, Liabilities	(23,986)	(2,898)
Total Liabilities	122,566	21,236
Fair Value, Measurements, Recurring [Member] | Fair Value Measurements, Significant Observable Inputs (Level 2) [Member] | Basis Swaps IFERC/NYMEX [Member]
Total commodity derivatives, Assets	0	0
Total commodity derivatives, Liabilities	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value Measurements, Significant Observable Inputs (Level 2) [Member] | Swing Swaps IFERC [Member]
Total commodity derivatives, Assets	20,744	120
Total commodity derivatives, Liabilities	(20,719)	(248)
Fair Value, Measurements, Recurring [Member] | Fair Value Measurements, Significant Observable Inputs (Level 2) [Member] | Fixed Swaps/Futures [Member]
Total commodity derivatives, Assets	158	0
Total commodity derivatives, Liabilities	(154)	0
Fair Value, Measurements, Recurring [Member] | Fair Value Measurements, Significant Observable Inputs (Level 2) [Member] | Forward Physical Swaps [Member]
Total commodity derivatives, Assets	738
Total commodity derivatives, Liabilities	(482)
Fair Value, Measurements, Recurring [Member] | Fair Value Measurements, Significant Observable Inputs (Level 2) [Member] | Propane - Forwards/Swaps [Member]
Total commodity derivatives, Assets	77	6,864
Total commodity derivatives, Liabilities	(2,086)
Fair Value, Measurements, Recurring [Member] | Fair Value Measurements, Significant Observable Inputs (Level 2) [Member] | Options - Puts [Member]
Total commodity derivatives, Assets	13,348	26,241
Total commodity derivatives, Liabilities	(423)	(7)
Fair Value, Measurements, Recurring [Member] | Fair Value Measurements, Significant Observable Inputs (Level 2) [Member] | Options - Calls [Member]
Total commodity derivatives, Assets		75
Total commodity derivatives, Liabilities	(122)	(2,643)
Fair Value, Measurements, Recurring [Member] | Basis Swaps IFERC/NYMEX [Member]
Total commodity derivatives, Assets	74,892	15,756
Total commodity derivatives, Liabilities	(68,918)	(17,372)
Fair Value, Measurements, Recurring [Member] | Swing Swaps IFERC [Member]
Total commodity derivatives, Assets	21,818	1,682
Total commodity derivatives, Liabilities	(22,707)	(3,768)
Fair Value, Measurements, Recurring [Member] | Fixed Swaps/Futures [Member]
Total commodity derivatives, Assets	70,270	42,474
Total commodity derivatives, Liabilities	(48,287)	(41,825)
Fair Value, Measurements, Recurring [Member] | Forward Physical Swaps [Member]
Total commodity derivatives, Assets	738
Total commodity derivatives, Liabilities	(482)
Fair Value, Measurements, Recurring [Member] | Propane - Forwards/Swaps [Member]
Total commodity derivatives, Assets	77	6,864
Total commodity derivatives, Liabilities	(2,086)
Fair Value, Measurements, Recurring [Member] | Options - Puts [Member]
Total commodity derivatives, Assets	13,348	26,241
Total commodity derivatives, Liabilities	(423)	(7)
Fair Value, Measurements, Recurring [Member] | Options - Calls [Member]
Total commodity derivatives, Assets		75
Total commodity derivatives, Liabilities	$ (122)	$ (2,643)