Derivative Financial Instruments Schedule of Derivative Offset Amounts (Details) - Exchange Traded [Member] - USD ($) $ in Thousands		Sep. 30, 2015		Dec. 31, 2014
Derivative [Line Items]
Derivative Asset, Fair Value, Gross Asset		$ 89,138		$ 106,764
Derivative Liability, Fair Value, Gross Liability		(10,695)		(10,622)
Derivative Asset, Fair Value, Amount Not Offset Against Collateral		78,443	[1]	96,142	[2]
Derivative, Collateral, Obligation to Return Cash		(49,447)		(78,279)
Amount After Offset	[3]	28,996		17,863
Other Current Liabilities [Member]
Derivative [Line Items]
Derivative Asset, Fair Value, Amount Not Offset Against Collateral				(5,413)
Other Noncurrent Assets [Member]
Derivative [Line Items]
Derivative Asset, Fair Value, Amount Not Offset Against Collateral		29,271		14,404
Other Current Assets [Member]
Derivative [Line Items]
Derivative Asset, Fair Value, Amount Not Offset Against Collateral		$ 49,172		$ 87,151

[1] Net amount includes energy commodity derivative contracts classified as current assets, net, of $49,172 and noncurrent assets of $29,271.

[2] Net amount includes energy commodity derivative contracts classified as current assets, net, of $87,151, current liabilities of $5,413 and noncurrent assets of $14,404.

[3] This represents the maximum amount of loss we would incur if all of our counterparties failed to perform on their derivative contracts.