Derivative Instrument and Hedging Activities 2 (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010
Derivatives, Fair Value [Line Items]
Derivative Fair Value Of Derivative Asset	$ 6,127	$ 16,931
Derivative Fair Value Of Derivative Liability	126,026	91,177
Cash Flow Hedges [Member]
Derivatives, Fair Value [Line Items]
Derivative Fair Value Of Derivative Asset	6,124	16,459
Derivative Fair Value Of Derivative Liability	85,865	24,346
Economic Hedges [Member]
Derivatives, Fair Value [Line Items]
Derivative Fair Value Of Derivative Asset	3	472
Derivative Fair Value Of Derivative Liability	40,161	66,831
Derivative Instruments Liabilitiy [Member] | Cash Flow Hedges [Member] | Interest Rate Contract [Member]
Derivatives, Fair Value [Line Items]
Derivative Fair Value Of Derivative Liability	19,936	19,694
Derivative Instruments Liabilitiy [Member] | Cash Flow Hedges [Member] | Gathering And Processing [Member] | Natural Gas Price Swaps [Member]
Derivatives, Fair Value [Line Items]
Derivative Fair Value Of Derivative Asset	0	16,459
Derivative Instruments Liabilitiy [Member] | Cash Flow Hedges [Member] | Gathering And Processing [Member] | NGL Price Swaps [Member]
Derivatives, Fair Value [Line Items]
Derivative Fair Value Of Derivative Liability	4,144	0
Derivative Instruments Liabilitiy [Member] | Economic Hedges [Member] | Gathering And Processing [Member] | NGL Processing Spread Swaps [Member]
Derivatives, Fair Value [Line Items]
Derivative Fair Value Of Derivative Liability	0	29,057
Derivative Instruments Liabilitiy [Member] | Economic Hedges [Member] | Gathering And Processing [Member] | Other Derivative Instruments [Member]
Derivatives, Fair Value [Line Items]
Derivative Fair Value Of Derivative Liability	50	0
Derivative Instruments Liabilitiy [Member] | Economic Hedges [Member] | Distribution [Member] | Natural Gas Price Swaps [Member]
Derivatives, Fair Value [Line Items]
Derivative Fair Value Of Derivative Asset	0	234
Derivative Fair Value Of Derivative Liability	34,468	34,968
Prepayments And Other Assets [Member] | Cash Flow Hedges [Member] | Gathering And Processing [Member] | Natural Gas Price Swaps [Member]
Derivatives, Fair Value [Line Items]
Derivative Fair Value Of Derivative Asset	6,124	0
Prepayments And Other Assets [Member] | Cash Flow Hedges [Member] | Gathering And Processing [Member] | NGL Price Swaps [Member]
Derivatives, Fair Value [Line Items]
Derivative Fair Value Of Derivative Liability	1,996	0
Prepayments And Other Assets [Member] | Economic Hedges [Member] | Gathering And Processing [Member] | Other Derivative Instruments [Member]
Derivatives, Fair Value [Line Items]
Derivative Fair Value Of Derivative Asset	0	133
Deferred Credits [Member] | Cash Flow Hedges [Member] | Interest Rate Contract [Member]
Derivatives, Fair Value [Line Items]
Derivative Fair Value Of Derivative Liability	59,789	4,652
Deferred Credits [Member] | Economic Hedges [Member] | Distribution [Member] | Natural Gas Price Swaps [Member]
Derivatives, Fair Value [Line Items]
Derivative Fair Value Of Derivative Asset	3	105
Derivative Fair Value Of Derivative Liability	$ 5,643	$ 2,806