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Derivatives And Risk Management (Energy Commodity Derivatives) (Details)
frequency in Thousands, Volt in Thousands
 6 Months Ended 12 Months Ended
Jun. 30, 2018
Volt
frequency
Dec. 31, 2017
Volt
frequency
Sales [Member] | Physical [Member] | Electric Derivative [Member]    
Energy Commodity Derivative Volumes [Line Items]    
2018 153 213
2019 156 94
2020 0 0
2021 0 0
2022 0 0
Thereafter 0 0
Sales [Member] | Physical [Member] | Gas Derivative [Member]    
Energy Commodity Derivative Volumes [Line Items]    
2018 | Volt 3,699 3,643
2019 | Volt 1,795 1,345
2020 | Volt 1,430 1,430
2021 1,049 1,049
2022 0 0
Thereafter | Volt 0 0
Sales [Member] | Financial [Member] | Electric Derivative [Member]    
Energy Commodity Derivative Volumes [Line Items]    
2018 967 1,739
2019 1,912 1,420
2020 836 589
2021 0 0
2022 0 0
Thereafter 0 0
Sales [Member] | Financial [Member] | Gas Derivative [Member]    
Energy Commodity Derivative Volumes [Line Items]    
2018 | Volt 39,963 67,375
2019 | Volt 40,363 35,438
2020 | Volt 3,500 915
2021 | Volt 450 0
2022 0 0
Thereafter | Volt 0 0
Purchase [Member] | Physical [Member] | Electric Derivative [Member]    
Energy Commodity Derivative Volumes [Line Items]    
2018 140 426
2019 173 235
2020 0 0
2021 0 0
2022 0 0
Thereafter 0 0
Purchase [Member] | Physical [Member] | Gas Derivative [Member]    
Energy Commodity Derivative Volumes [Line Items]    
2018 | Volt 8,399 10,572
2019 | Volt 610 610
2020 | Volt 910 910
2021 | Volt 0 0
2022 | Volt 0 0
Thereafter | Volt 0 0
Purchase [Member] | Financial [Member] | Electric Derivative [Member]    
Energy Commodity Derivative Volumes [Line Items]    
2018 450 763
2019 737 737
2020 0 0
2021 0 0
2022 0 0
Thereafter 0 0
Purchase [Member] | Financial [Member] | Gas Derivative [Member]    
Energy Commodity Derivative Volumes [Line Items]    
2018 | Volt 65,063 107,580
2019 | Volt 73,923 61,073
2020 | Volt 27,265 16,590
2021 | Volt 2,250 0
2022 | Volt 0 0
Thereafter | Volt 0 0