Derivatives And Risk Management (Energy Commodity Derivatives) (Details) frequency in Thousands, Volt in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2016 Volt frequency	Dec. 31, 2015 Volt frequency
Sales [Member] | Physical [Member] | Electric Derivative [Member]
Energy Commodity Derivative Volumes [Line Items]
2016	200	280
2017	255	255
2018	286	286
2019	158	158
2020	0	0
Thereafter	0	0
Sales [Member] | Physical [Member] | Gas Derivative [Member]
Energy Commodity Derivative Volumes [Line Items]
2016 | Volt	968	3,182
2017 | Volt	1,360	1,360
2018 | Volt	1,360	1,360
2019	1,345	1,345
2020	1,430	1,430
Thereafter | Volt	1,060	1,060
Sales [Member] | Financial [Member] | Electric Derivative [Member]
Energy Commodity Derivative Volumes [Line Items]
2016	1,916	2,656
2017	483	483
2018	192	0
2019	0	0
2020	0	0
Thereafter	0	0
Sales [Member] | Financial [Member] | Gas Derivative [Member]
Energy Commodity Derivative Volumes [Line Items]
2016 | Volt	104,118	112,233
2017 | Volt	41,918	26,965
2018 | Volt	6,363	2,738
2019 | Volt	0	0
2020	0	0
Thereafter | Volt	0	0
Purchase [Member] | Physical [Member] | Electric Derivative [Member]
Energy Commodity Derivative Volumes [Line Items]
2016	213	407
2017	397	397
2018	397	397
2019	235	235
2020	0	0
Thereafter	0	0
Purchase [Member] | Physical [Member] | Gas Derivative [Member]
Energy Commodity Derivative Volumes [Line Items]
2016 | Volt	13,846	17,252
2017 | Volt	1,265	675
2018 | Volt	0	0
2019 | Volt	610	305
2020 | Volt	910	455
Thereafter | Volt	0	0
Purchase [Member] | Financial [Member] | Electric Derivative [Member]
Energy Commodity Derivative Volumes [Line Items]
2016	1,643	1,954
2017	97	97
2018	0	0
2019	0	0
2020	0	0
Thereafter	0	0
Purchase [Member] | Financial [Member] | Gas Derivative [Member]
Energy Commodity Derivative Volumes [Line Items]
2016 | Volt	127,565	142,693
2017 | Volt	58,238	49,200
2018 | Volt	23,903	15,118
2019 | Volt	10,245	6,935
2020 | Volt	1,815	905
Thereafter | Volt	0	0