Derivatives (Derivatives Outstanding) (Details) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2013		Dec. 31, 2012
Derivative [Line Items]
Mark to Market Derivatives, Fair Value	$ 2,727		$ 1,924
Cash Flow Liquid Swap [Member] | Short Contracts [Member] | Liquids [Member]
Derivative [Line Items]
Derivative nonmonetary notional amount (volume)	(9,285,000)
Cash Flow Hedges, Fair Value	1,179
Swing swap [Member] | Short Contracts [Member]
Derivative [Line Items]
Derivative nonmonetary notional amount (volume)	(1,008,000)	[1]
Mark to Market Derivatives, Fair Value	0	[1]
Swing swap [Member] | Long Contracts [Member]
Derivative [Line Items]
Derivative nonmonetary notional amount (volume)	930,000	[1]
Mark to Market Derivatives, Fair Value	135	[1]
Physical offset to swing swap [Member] | Short Contracts [Member]
Derivative [Line Items]
Derivative nonmonetary notional amount (volume)	(930,000)	[1]
Mark to Market Derivatives, Fair Value	(112)	[1]
Physical offset to swing swap [Member] | Long Contracts [Member]
Derivative [Line Items]
Derivative nonmonetary notional amount (volume)	1,008,000	[1]
Mark to Market Derivatives, Fair Value	0	[1]
Basis Swap [Member] | Short Contracts [Member]
Derivative [Line Items]
Derivative nonmonetary notional amount (volume)	(636,000)
Mark to Market Derivatives, Fair Value	4
Basis Swap [Member] | Short Contracts [Member] | Liquids [Member]
Derivative [Line Items]
Derivative nonmonetary notional amount (volume)	(2,559,000)
Mark to Market Derivatives, Fair Value	837
Basis Swap [Member] | Long Contracts [Member]
Derivative [Line Items]
Derivative nonmonetary notional amount (volume)	636,000
Mark to Market Derivatives, Fair Value	(35)
Physical Offset To Basis Swap [Member] | Short Contracts [Member]
Derivative [Line Items]
Derivative nonmonetary notional amount (volume)	(636,000)
Mark to Market Derivatives, Fair Value	2,042
Physical Offset To Basis Swap [Member] | Long Contracts [Member]
Derivative [Line Items]
Derivative nonmonetary notional amount (volume)	636,000
Mark to Market Derivatives, Fair Value	(2,255)
Processing Margin Hedges [Member] | Short Contracts [Member] | Liquids [Member]
Derivative [Line Items]
Derivative nonmonetary notional amount (volume)	(4,634,000)
Mark to Market Derivatives, Fair Value	1,182
Processing Margin Hedges [Member] | Long Contracts [Member] | Gas [Member]
Derivative [Line Items]
Derivative nonmonetary notional amount (volume)	494,000
Mark to Market Derivatives, Fair Value	(89)
Storage Swap [Member] | Short Contracts [Member] | Gas [Member]
Derivative [Line Items]
Derivative nonmonetary notional amount (volume)	(100,000)
Mark to Market Derivatives, Fair Value	14
Storage Swap [Member] | Short Contracts [Member] | Liquids [Member]
Derivative [Line Items]
Derivative nonmonetary notional amount (volume)	(1,890,000)
Mark to Market Derivatives, Fair Value	16
Storage Swap [Member] | Short Contracts [Member] | Condensate Inventory [Member]
Derivative [Line Items]
Derivative nonmonetary notional amount (volume)	(31,000)
Mark to Market Derivatives, Fair Value	(191)
Not Designated as Hedging Instrument [Member]
Derivative [Line Items]
Mark to Market Derivatives, Fair Value	$ 1,548

[1] All are gas contracts except for liquids swaps (designated or non-designated), processing margin hedges - liquids, storage swap transactions - liquids inventory and storage swap transactions - condensate inventory.