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Derivatives And Risk Management (Energy Commodity Derivatives) (Details) frequency in Thousands, Volt in Thousands	12 Months Ended
	Dec. 31, 2017 Volt frequency	Dec. 31, 2016 Volt frequency
Sales [Member] | Electric Derivative [Member] | Physical [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Settled in 1 Year	213	316
Settled in 2 Years	94	286
Settled in 3 Years	0	158
Settled in 4 Years	0	0
Settled in 5 Years	0	0
Thereafter	0	0
Sales [Member] | Electric Derivative [Member] | Financial [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Settled in 1 Year	1,739	1,552
Settled in 2 Years	1,420	1,244
Settled in 3 Years	589	982
Settled in 4 Years	0	0
Settled in 5 Years	0	0
Thereafter	0	0
Sales [Member] | Gas Derivative [Member] | Physical [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Settled in 1 Year | Volt	3,643	4,165
Settled in 2 Years | Volt	1,345	1,360
Settled in 3 Years | Volt	1,430	1,345
Settled in 4 Years	1,049	1,430
Settled in 5 Years	0	1,060
Thereafter | Volt	0	0
Sales [Member] | Gas Derivative [Member] | Financial [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Settled in 1 Year | Volt	67,375	73,110
Settled in 2 Years | Volt	35,438	15,113
Settled in 3 Years | Volt	915	4,020
Settled in 4 Years | Volt	0	0
Settled in 5 Years	0	0
Thereafter | Volt	0	0
Purchase [Member] | Electric Derivative [Member] | Physical [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Settled in 1 Year	426	510
Settled in 2 Years	235	397
Settled in 3 Years	0	235
Settled in 4 Years	0	0
Settled in 5 Years	0	0
Thereafter	0	0
Purchase [Member] | Electric Derivative [Member] | Financial [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Settled in 1 Year	763	907
Settled in 2 Years	737	0
Settled in 3 Years	0	0
Settled in 4 Years	0	0
Settled in 5 Years	0	0
Thereafter	0	0
Purchase [Member] | Gas Derivative [Member] | Physical [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Settled in 1 Year | Volt	10,572	15,475
Settled in 2 Years | Volt	610	0
Settled in 3 Years | Volt	910	610
Settled in 4 Years | Volt	0	910
Settled in 5 Years | Volt	0	0
Thereafter | Volt	0	0
Purchase [Member] | Gas Derivative [Member] | Financial [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Settled in 1 Year | Volt	107,580	110,380
Settled in 2 Years | Volt	61,073	52,755
Settled in 3 Years | Volt	16,590	29,475
Settled in 4 Years | Volt	0	2,725
Settled in 5 Years | Volt	0	0
Thereafter | Volt	0	0

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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