Derivatives And Risk Management (Energy Commodity Derivatives) (Details) frequency in Thousands, Volt in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2017 Volt frequency	Dec. 31, 2016 Volt frequency
Sales [Member] | Physical [Member] | Electric Derivative [Member]
Energy Commodity Derivative Volumes [Line Items]
2017	149	316
2018	286	286
2019	126	158
2020	0	0
2021	0	0
Thereafter	0	0
Sales [Member] | Physical [Member] | Gas Derivative [Member]
Energy Commodity Derivative Volumes [Line Items]
2017 | Volt	4,448	4,165
2018 | Volt	1,360	1,360
2019 | Volt	1,345	1,345
2020	1,430	1,430
2021	1,049	1,060
Thereafter | Volt	0	0
Sales [Member] | Financial [Member] | Electric Derivative [Member]
Energy Commodity Derivative Volumes [Line Items]
2017	1,101	1,552
2018	1,244	1,244
2019	982	982
2020	0	0
2021	0	0
Thereafter	0	0
Sales [Member] | Financial [Member] | Gas Derivative [Member]
Energy Commodity Derivative Volumes [Line Items]
2017 | Volt	61,633	73,110
2018 | Volt	33,188	15,113
2019 | Volt	19,598	4,020
2020 | Volt	0	0
2021	0	0
Thereafter | Volt	0	0
Purchase [Member] | Physical [Member] | Electric Derivative [Member]
Energy Commodity Derivative Volumes [Line Items]
2017	214	510
2018	397	397
2019	235	235
2020	0	0
2021	0	0
Thereafter	0	0
Purchase [Member] | Physical [Member] | Gas Derivative [Member]
Energy Commodity Derivative Volumes [Line Items]
2017 | Volt	8,891	15,475
2018 | Volt	0	0
2019 | Volt	610	610
2020 | Volt	910	910
2021 | Volt	0	0
Thereafter | Volt	0	0
Purchase [Member] | Financial [Member] | Electric Derivative [Member]
Energy Commodity Derivative Volumes [Line Items]
2017	1,044	907
2018	246	0
2019	737	0
2020	0	0
2021	0	0
Thereafter	0	0
Purchase [Member] | Financial [Member] | Gas Derivative [Member]
Energy Commodity Derivative Volumes [Line Items]
2017 | Volt	83,808	110,380
2018 | Volt	64,415	52,755
2019 | Volt	35,623	29,475
2020 | Volt	2,725	2,725
2021 | Volt	0	0
Thereafter | Volt	0	0