Derivatives And Risk Management (Derivative Instruments Summary) (Details) - USD ($)	Dec. 31, 2019	Dec. 31, 2018
Derivatives, Fair Value [Line Items]
Asset	$ 43,222,000	$ 46,849,000
Liability	(82,203,000)	(102,453,000)
Collateral Netting	10,148,000	51,747,000
Net Asset (Liability)	(28,833,000)	(3,857,000)
Interest Rate Swap [Member]
Derivatives, Fair Value [Line Items]
Collateral Netting	6,770,000	530,000
Collateral Already Posted, Aggregate Fair Value	6,770,000	530,000
Commodity Contract [Member]
Derivatives, Fair Value [Line Items]
Collateral Netting	3,378,000	51,217,000
Collateral Already Posted, Aggregate Fair Value	7,812,000	78,025,000
Other Current Assets [Member] \| Foreign Currency Exchange Contracts [Member]
Derivatives, Fair Value [Line Items]
Asset	97,000
Liability	0
Collateral Netting	0
Net Asset (Liability)	97,000
Other Current Assets [Member] \| Interest Rate Swap [Member]
Derivatives, Fair Value [Line Items]
Asset	589,000	5,283,000
Liability	0	0
Collateral Netting	0	0
Net Asset (Liability)	589,000	5,283,000
Other Current Assets [Member] \| Commodity Contract [Member]
Derivatives, Fair Value [Line Items]
Asset	416,000	400,000
Liability	(245,000)	(130,000)
Collateral Netting	0	0
Net Asset (Liability)	171,000	270,000
Other Noncurrent Assets [Member] \| Interest Rate Swap [Member]
Derivatives, Fair Value [Line Items]
Asset		5,283,000
Liability		(440,000)
Collateral Netting		0
Net Asset (Liability)		4,843,000
Other Noncurrent Assets [Member] \| Commodity Contract [Member]
Derivatives, Fair Value [Line Items]
Asset	6,369,000
Liability	(5,446,000)
Collateral Netting	0
Net Asset (Liability)	923,000
Other Noncurrent Liabilities [Member] \| Interest Rate Swap [Member]
Derivatives, Fair Value [Line Items]
Asset	725,000	0
Liability	(24,677,000)	(7,391,000)
Collateral Netting	5,454,000	530,000
Net Asset (Liability)	(18,498,000)	(6,861,000)
Other Noncurrent Liabilities [Member] \| Commodity Contract [Member]
Derivatives, Fair Value [Line Items]
Asset	28,000	4,426,000
Liability	(1,215,000)	(21,292,000)
Collateral Netting	0	13,427,000
Net Asset (Liability)	(1,187,000)	(3,439,000)
Other Current Liabilities [Member] \| Foreign Currency Exchange Contracts [Member]
Derivatives, Fair Value [Line Items]
Asset		0
Liability		(45,000)
Collateral Netting		0
Net Asset (Liability)		(45,000)
Other Current Liabilities [Member] \| Interest Rate Swap [Member]
Derivatives, Fair Value [Line Items]
Asset	238,000
Liability	(9,379,000)
Collateral Netting	1,316,000
Net Asset (Liability)	(7,825,000)
Other Current Liabilities [Member] \| Commodity Contract [Member]
Derivatives, Fair Value [Line Items]
Asset	34,760,000	31,457,000
Liability	(41,241,000)	(73,155,000)
Collateral Netting	3,378,000	37,790,000
Net Asset (Liability)	$ (3,103,000)	$ (3,908,000)

The aggregate fair value of assets that are already posted, at the end of the reporting period, as collateral for derivative instruments with credit-risk-related contingent features.

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