Derivatives And Risk Management Derivatives and Risk Management (Collateral) (Details) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Derivative [Line Items]
Derivative, Fair Value, Amount Offset Against Collateral, Net	$ 48,556	$ 44,390
Commodity Contract [Member]
Derivative [Line Items]
Liability position at aggregate fair value	7,090	12,911
Collateral Already Posted, Aggregate Fair Value	28,716	20,565
Letters of credit outstanding	28,200	14,500
Derivative, Fair Value, Amount Offset Against Collateral, Net	14,526	15,510
Additional Collateral, Aggregate Fair Value	6,980	16,227
Interest Rate Swap [Member]
Derivative [Line Items]
Collateral Already Posted, Aggregate Fair Value	34,030	28,880
Letters of credit outstanding	9,600	10,900
Derivative, Fair Value, Amount Offset Against Collateral, Net	34,030	28,880
Interest Rate Contracts [Member]
Derivative [Line Items]
Liability position at aggregate fair value	85,498	77,568
Additional Collateral, Aggregate Fair Value	$ 18,750	$ 19,404