Derivative Financial Instruments Schedule of Derivative Offset Amounts (Details) - Exchange Traded [Member] - USD ($) $ in Thousands		Mar. 31, 2016		Dec. 31, 2015
Derivative [Line Items]
Derivative Asset, Fair Value, Gross Asset		$ 24,081		$ 48,367
Derivative Liability, Fair Value, Gross Liability		(1,489)		(5,646)
Derivative Asset, Fair Value, Amount Not Offset Against Collateral		22,592	[1]	42,721	[2]
Derivative, Collateral, Obligation to Return Cash		(3,991)		(24,252)
Amount After Offset	[3]	18,601		18,469
Other Noncurrent Assets [Member]
Derivative [Line Items]
Derivative Asset, Fair Value, Amount Not Offset Against Collateral		4,831		3,478
Other Current Assets [Member]
Derivative [Line Items]
Derivative Asset, Fair Value, Amount Not Offset Against Collateral		$ 17,761		$ 39,243

[1] Net amount includes energy commodity derivative contracts classified as current assets, net, of $17,761 and noncurrent assets of $4,831.

[2] Net amount includes energy commodity derivative contracts classified as current assets, net, of $39,243 and noncurrent assets of $3,478.

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