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Fair Value (Fair Value Of Assets And Liabilities Measured On Recurring Basis) (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Asset	$ 46,849	$ 51,506
Liability	102,453	161,467
Cash and cash equivalents	14,656	16,172	$ 8,507	$ 10,484
Fixed Income Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	500	200
Fair Value, Measurements, Recurring [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Counterparty and Cash Collateral Netting	(36,453)	(45,308)
Total	18,298	14,467
Counterparty and Cash Collateral Netting	(88,200)	(107,716)
Total	14,253	53,751
Fair Value, Measurements, Recurring [Member] \| Energy commodity derivatives [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Counterparty and Cash Collateral Netting	(35,982)	(42,550)
Derivative Asset	270	1,264
Counterparty and Cash Collateral Netting	(87,199)	(69,988)
Derivative Liability	2,084	1,354
Fair Value, Measurements, Recurring [Member] \| Power Exchange Agreements [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Liability	2,488
Counterparty and Cash Collateral Netting	0	0
Derivative Liability	2,488	13,245
Fair Value, Measurements, Recurring [Member] \| Natural Gas Exchange Agreements [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Counterparty and Cash Collateral Netting	(31)	(183)
Derivative Asset	0	0
Liability	2,774
Counterparty and Cash Collateral Netting	(31)	(183)
Derivative Liability	2,774	3,164
Fair Value, Measurements, Recurring [Member] \| Commodity Option [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Counterparty and Cash Collateral Netting	0	0
Derivative Liability	1	19
Fair Value, Measurements, Recurring [Member] \| Interest Rate Swap [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Counterparty and Cash Collateral Netting	(440)	(2,574)
Derivative Asset	10,126	4,903
Counterparty and Cash Collateral Netting	(970)	(37,544)
Derivative Liability	6,861	35,969
Fair Value, Measurements, Recurring [Member] \| Foreign Exchange Contract [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Counterparty and Cash Collateral Netting		(1)
Derivative Asset		31
Counterparty and Cash Collateral Netting	0	(1)
Derivative Liability	45	0
Fair Value, Measurements, Recurring [Member] \| Level 1 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total	7,902	8,269
Total	0	0
Fair Value, Measurements, Recurring [Member] \| Level 2 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total	46,818	51,323
Total	97,159	144,856
Fair Value, Measurements, Recurring [Member] \| Level 2 [Member] \| Energy commodity derivatives [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Asset	36,252	43,814
Liability	89,283	71,342
Fair Value, Measurements, Recurring [Member] \| Level 2 [Member] \| Interest Rate Swap [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Asset	10,566	7,477
Liability	7,831	73,513
Fair Value, Measurements, Recurring [Member] \| Level 2 [Member] \| Foreign Exchange Contract [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Asset		32
Liability	45	1
Fair Value, Measurements, Recurring [Member] \| Level 3 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total	31	183
Total	5,294	16,611
Fair Value, Measurements, Recurring [Member] \| Level 3 [Member] \| Power Exchange Agreements [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Liability	2,488	13,245
Fair Value, Measurements, Recurring [Member] \| Level 3 [Member] \| Natural Gas Exchange Agreements [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Asset	31	183
Liability	2,805	3,347
Fair Value, Measurements, Recurring [Member] \| Level 3 [Member] \| Commodity Option [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Liability	1	19
Fixed Income Funds [Member] \| Fair Value, Measurements, Recurring [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Deferred compensation assets:	1,745	1,638
Fixed Income Funds [Member] \| Fair Value, Measurements, Recurring [Member] \| Level 1 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Deferred compensation assets:	1,745	1,638
Equity Funds [Member] \| Fair Value, Measurements, Recurring [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Deferred compensation assets:	6,157	6,631
Equity Funds [Member] \| Fair Value, Measurements, Recurring [Member] \| Level 1 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Deferred compensation assets:	$ 6,157	$ 6,631