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Fair Value (Fair Value Of Assets And Liabilities Measured On Recurring Basis) (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Asset	$ 43,222	$ 46,849
Liability	82,203	102,453
Cash and cash equivalents	9,896	14,656	$ 16,172	$ 8,507
Fixed Income Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	400	500
Fair Value, Recurring [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Counterparty and Cash Collateral Netting	(41,442)	(36,453)
Total	10,283	18,298
Counterparty and Cash Collateral Netting	(51,590)	(88,200)
Total	30,613	14,253
Fair Value, Recurring [Member] \| Energy commodity derivatives [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Counterparty and Cash Collateral Netting	(40,452)	(35,982)
Derivative Asset	1,094	270
Counterparty and Cash Collateral Netting	(43,830)	(87,199)
Derivative Liability	1,314	2,084
Fair Value, Recurring [Member] \| Power Exchange Agreements [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Counterparty and Cash Collateral Netting		0
Derivative Liability		2,488
Fair Value, Recurring [Member] \| Natural Gas Exchange Agreements [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Counterparty and Cash Collateral Netting	(27)	(31)
Derivative Asset	0	0
Liability	2,976
Counterparty and Cash Collateral Netting	(27)	(31)
Derivative Liability	2,976	2,774
Fair Value, Recurring [Member] \| Commodity Option [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Counterparty and Cash Collateral Netting		0
Derivative Liability		1
Fair Value, Recurring [Member] \| Interest Rate Swap [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Counterparty and Cash Collateral Netting	(963)	(440)
Derivative Asset	589	10,126
Counterparty and Cash Collateral Netting	(7,733)	(970)
Derivative Liability	26,323	6,861
Fair Value, Recurring [Member] \| Foreign Exchange Contract [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Counterparty and Cash Collateral Netting	0
Derivative Asset	97
Counterparty and Cash Collateral Netting		0
Derivative Liability		45
Fair Value, Recurring [Member] \| Level 1 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total	8,503	7,902
Total	0	0
Fair Value, Recurring [Member] \| Level 2 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total	43,195	46,818
Total	79,200	97,159
Fair Value, Recurring [Member] \| Level 2 [Member] \| Energy commodity derivatives [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Asset	41,546	36,252
Liability	45,144	89,283
Fair Value, Recurring [Member] \| Level 2 [Member] \| Interest Rate Swap [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Asset	1,552	10,566
Liability	34,056	7,831
Fair Value, Recurring [Member] \| Level 2 [Member] \| Foreign Exchange Contract [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Asset	97
Liability		45
Fair Value, Recurring [Member] \| Level 3 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total	27	31
Total	3,003	5,294
Fair Value, Recurring [Member] \| Level 3 [Member] \| Power Exchange Agreements [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Liability		2,488
Fair Value, Recurring [Member] \| Level 3 [Member] \| Natural Gas Exchange Agreements [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Asset	27	31
Liability	3,003	2,805
Fair Value, Recurring [Member] \| Level 3 [Member] \| Commodity Option [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Liability		1
Fixed Income Funds [Member] \| Fair Value, Recurring [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Deferred compensation assets:	2,232	1,745
Fixed Income Funds [Member] \| Fair Value, Recurring [Member] \| Level 1 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Deferred compensation assets:	2,232	1,745
Equity Funds [Member] \| Fair Value, Recurring [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Deferred compensation assets:	6,271	6,157
Equity Funds [Member] \| Fair Value, Recurring [Member] \| Level 1 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Deferred compensation assets:	$ 6,271	$ 6,157