Derivatives (Derivatives Outstanding) (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013
Derivative [Line Items]
Derivative Assets (Liabilities), at Fair Value, Net	$ 1,935
Cash Flow Liquid Swap [Member] | Short Contracts [Member] | Liquids [Member]
Derivative [Line Items]
Derivative Nonmonetary Notional Amount	(7,076,000)
Cash Flow Hedges Derivative Instruments at Fair Value, Net	505
Swing swap [Member] | Short Contracts [Member]
Derivative [Line Items]
Derivative Nonmonetary Notional Amount	(1,014,000)
Derivative Assets (Liabilities), at Fair Value, Net	0
Physical offset to swing swap [Member] | Long Contracts [Member]
Derivative [Line Items]
Derivative Nonmonetary Notional Amount	1,014,000
Derivative Assets (Liabilities), at Fair Value, Net	0
Basis Swap [Member] | Short Contracts [Member]
Derivative [Line Items]
Derivative Nonmonetary Notional Amount	(450,000)
Derivative Assets (Liabilities), at Fair Value, Net	8
Basis Swap [Member] | Short Contracts [Member] | Liquids [Member]
Derivative [Line Items]
Derivative Nonmonetary Notional Amount	(3,407,000)
Derivative Assets (Liabilities), at Fair Value, Net	792
Basis Swap [Member] | Long Contracts [Member]
Derivative [Line Items]
Derivative Nonmonetary Notional Amount	450,000
Derivative Assets (Liabilities), at Fair Value, Net	0
Physical Offset To Basis Swap [Member] | Short Contracts [Member]
Derivative [Line Items]
Derivative Nonmonetary Notional Amount	(450,000)
Derivative Assets (Liabilities), at Fair Value, Net	1,585
Physical Offset To Basis Swap [Member] | Long Contracts [Member]
Derivative [Line Items]
Derivative Nonmonetary Notional Amount	450,000
Derivative Assets (Liabilities), at Fair Value, Net	(1,745)
Processing Margin Hedges [Member] | Short Contracts [Member] | Liquids [Member]
Derivative [Line Items]
Derivative Nonmonetary Notional Amount	(4,483,000)
Derivative Assets (Liabilities), at Fair Value, Net	1,059
Processing Margin Hedges [Member] | Long Contracts [Member] | Gas [Member]
Derivative [Line Items]
Derivative Nonmonetary Notional Amount	523,000
Derivative Assets (Liabilities), at Fair Value, Net	272
Storage Swap [Member] | Short Contracts [Member] | Gas [Member]
Derivative [Line Items]
Derivative Nonmonetary Notional Amount	(100,000)
Derivative Assets (Liabilities), at Fair Value, Net	(35)
Storage Swap [Member] | Short Contracts [Member] | Liquids [Member]
Derivative [Line Items]
Derivative Nonmonetary Notional Amount	(840,000)
Derivative Assets (Liabilities), at Fair Value, Net	$ (1)