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Fair Value (Fair Value Of Assets And Liabilities Measured On Recurring Basis) (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018	Sep. 30, 2018	Dec. 31, 2017
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Gross Asset	$ 35,595	$ 46,849
Liability	96,278	102,453
Cash and cash equivalents	14,454	14,656	$ 21,170	$ 16,172
Fixed Income Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	400	500
Fair Value, Measurements, Recurring [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Counterparty and collateral netting, assets	(34,714)	(36,453)
Assets, Fair Value Disclosure	9,290	18,298
Counterparty and collateral netting, liabilities	(47,099)	(88,200)
Financial Liabilities Fair Value Disclosure	49,179	14,253
Fair Value, Measurements, Recurring [Member] \| Natural Gas Exchange Agreements [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Counterparty and collateral netting, assets	(43)	(31)
Derivative Asset	0	0
Counterparty and collateral netting, liabilities	(43)	(31)
Derivative Liability	3,134	2,774
Fair Value, Measurements, Recurring [Member] \| Power Exchange Agreements [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Counterparty and collateral netting, liabilities		0
Derivative Liability		2,488
Fair Value, Measurements, Recurring [Member] \| Interest Rate Swap [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Counterparty and collateral netting, assets		(440)
Derivative Asset		10,126
Counterparty and collateral netting, liabilities	(8,880)	(970)
Derivative Liability	44,391	6,861
Fair Value, Measurements, Recurring [Member] \| Energy commodity derivatives
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Counterparty and collateral netting, assets	(34,671)	(35,982)
Derivative Asset	881	270
Counterparty and collateral netting, liabilities	(38,176)	(87,199)
Derivative Liability	1,633	2,084
Fair Value, Measurements, Recurring [Member] \| Power Option Agreement [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Counterparty and collateral netting, liabilities		0
Derivative Liability		1
Fair Value, Measurements, Recurring [Member] \| Foreign Exchange Contract [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Counterparty and collateral netting, liabilities	0	0
Derivative Liability	21	45
Fair Value, Measurements, Recurring [Member] \| Level 1 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets, Fair Value Disclosure	8,409	7,902
Financial Liabilities Fair Value Disclosure	0	0
Fair Value, Measurements, Recurring [Member] \| Level 2 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets, Fair Value Disclosure	35,552	46,818
Financial Liabilities Fair Value Disclosure	93,101	97,159
Fair Value, Measurements, Recurring [Member] \| Level 2 [Member] \| Interest Rate Swap [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Gross Asset		10,566
Liability	53,271	7,831
Fair Value, Measurements, Recurring [Member] \| Level 2 [Member] \| Energy commodity derivatives
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Gross Asset	35,552	36,252
Liability	39,809	89,283
Fair Value, Measurements, Recurring [Member] \| Level 2 [Member] \| Foreign Exchange Contract [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Liability	21	45
Fair Value, Measurements, Recurring [Member] \| Level 3 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets, Fair Value Disclosure	43	31
Financial Liabilities Fair Value Disclosure	3,177	5,294
Fair Value, Measurements, Recurring [Member] \| Level 3 [Member] \| Natural Gas Exchange Agreements [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Gross Asset	43	31
Liability	3,177	2,805
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
Fair Value, Measurements, Recurring [Member] \| Level 3 [Member] \| Power Option Agreement [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Liability		1
Fixed Income Funds [Member] \| Fair Value, Measurements, Recurring [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Deferred compensation assets:	1,818	1,745
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:	1,818	1,745
Equity Funds [Member] \| Fair Value, Measurements, Recurring [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Deferred compensation assets:	6,591	6,157
Equity Funds [Member] \| Fair Value, Measurements, Recurring [Member] \| Level 1 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Deferred compensation assets:	$ 6,591	$ 6,157