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Fair Value (Fair Value Of Assets And Liabilities Measured On Recurring Basis) (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019	Mar. 31, 2019	Dec. 31, 2018
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Gross Asset	$ 35,123	$ 43,222
Liability	145,084	82,203
Cash and cash equivalents	18,919	9,896	$ 14,861	$ 14,656
Fixed Income Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	400	400
Fair Value, Recurring [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Counterparty and collateral netting, assets	(30,911)	(41,442)
Assets, Fair Value Disclosure	12,439	10,283
Counterparty and collateral netting, liabilities	(57,306)	(51,590)
Financial Liabilities Fair Value Disclosure	87,778	30,613
Fair Value, Recurring [Member] \| Natural Gas Exchange Agreements [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Counterparty and collateral netting, assets	(26)	(27)
Derivative Asset	0	0
Counterparty and collateral netting, liabilities	(26)	(27)
Derivative Liability	2,253	2,976
Fair Value, Recurring [Member] \| Interest Rate Swap [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Counterparty and collateral netting, assets		(963)
Derivative Asset		589
Counterparty and collateral netting, liabilities	(27,090)	(7,733)
Derivative Liability	85,148	26,323
Fair Value, Recurring [Member] \| Energy commodity derivatives
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Counterparty and collateral netting, assets	(30,849)	(40,452)
Derivative Asset	4,212	1,094
Counterparty and collateral netting, liabilities	(30,154)	(43,830)
Derivative Liability	310	1,314
Fair Value, Recurring [Member] \| Foreign Exchange Contract [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Counterparty and collateral netting, assets	(36)
Derivative Asset	0	97
Counterparty and collateral netting, liabilities	(36)
Derivative Liability	67
Fair Value, Recurring [Member] \| Level 1 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets, Fair Value Disclosure	8,227	8,503
Financial Liabilities Fair Value Disclosure	0	0
Fair Value, Recurring [Member] \| Level 2 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets, Fair Value Disclosure	35,097	43,195
Financial Liabilities Fair Value Disclosure	142,805	79,200
Fair Value, Recurring [Member] \| Level 2 [Member] \| Interest Rate Swap [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Gross Asset		1,552
Liability	112,238	34,056
Fair Value, Recurring [Member] \| Level 2 [Member] \| Energy commodity derivatives
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Gross Asset	35,061	41,546
Liability	30,464	45,144
Fair Value, Recurring [Member] \| Level 2 [Member] \| Foreign Exchange Contract [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Gross Asset	36	97
Liability	103
Fair Value, Recurring [Member] \| Level 3 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets, Fair Value Disclosure	26	27
Financial Liabilities Fair Value Disclosure	2,279	3,003
Fair Value, Recurring [Member] \| Level 3 [Member] \| Natural Gas Exchange Agreements [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Gross Asset	26	27
Liability	2,279	3,003
Fixed Income Funds [Member] \| Fair Value, Recurring [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Deferred compensation assets:	2,642	2,232
Fixed Income Funds [Member] \| Fair Value, Recurring [Member] \| Level 1 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Deferred compensation assets:	2,642	2,232
Equity Funds [Member] \| Fair Value, Recurring [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Deferred compensation assets:	5,585	6,271
Equity Funds [Member] \| Fair Value, Recurring [Member] \| Level 1 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Deferred compensation assets:	$ 5,585	$ 6,271