Derivatives And Risk Management (Derivative Instruments Summary) (Details) - USD ($)	Dec. 31, 2018	Dec. 31, 2017
Derivatives, Fair Value [Line Items]
Asset	$ 46,849,000	$ 51,506,000
Liability	(102,453,000)	(161,467,000)
Collateral Netting	51,747,000	62,408,000
Net Asset (Liability)	(3,857,000)	(47,553,000)
Interest Rate Swap [Member]
Derivatives, Fair Value [Line Items]
Collateral Netting	530,000	34,970,000
Collateral Already Posted, Aggregate Fair Value	530,000	34,970,000
Commodity Contract [Member]
Derivatives, Fair Value [Line Items]
Collateral Netting	51,217,000	27,438,000
Collateral Already Posted, Aggregate Fair Value	78,025,000	39,458,000
Other Current Assets [Member] | Foreign Currency Exchange Contracts [Member]
Derivatives, Fair Value [Line Items]
Asset		32,000
Liability		(1,000)
Collateral Netting		0
Net Asset (Liability)		31,000
Other Current Assets [Member] | Interest Rate Swap [Member]
Derivatives, Fair Value [Line Items]
Asset	5,283,000	2,597,000
Liability	0	(270,000)
Collateral Netting	0	0
Net Asset (Liability)	5,283,000	2,327,000
Other Current Assets [Member] | Commodity Contract [Member]
Derivatives, Fair Value [Line Items]
Asset	400,000	1,386,000
Liability	(130,000)	(122,000)
Collateral Netting	0	0
Net Asset (Liability)	270,000	1,264,000
Other Property And Investments Net And Other Non-current Assets [Member] | Interest Rate Swap [Member]
Derivatives, Fair Value [Line Items]
Asset	5,283,000	4,880,000
Liability	(440,000)	(2,304,000)
Collateral Netting	0	0
Net Asset (Liability)	4,843,000	2,576,000
Other Noncurrent Liabilities [Member] | Interest Rate Swap [Member]
Derivatives, Fair Value [Line Items]
Asset	0	0
Liability	(7,391,000)	(7,540,000)
Collateral Netting	530,000	6,018,000
Net Asset (Liability)	(6,861,000)	(1,522,000)
Other Noncurrent Liabilities [Member] | Commodity Contract [Member]
Derivatives, Fair Value [Line Items]
Asset	4,426,000	15,970,000
Liability	(21,292,000)	(34,936,000)
Collateral Netting	13,427,000	10,032,000
Net Asset (Liability)	(3,439,000)	(8,934,000)
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		0
Liability		(63,399,000)
Collateral Netting		28,952,000
Net Asset (Liability)		(34,447,000)
Other Current Liabilities [Member] | Commodity Contract [Member]
Derivatives, Fair Value [Line Items]
Asset	31,457,000	26,641,000
Liability	(73,155,000)	(52,895,000)
Collateral Netting	37,790,000	17,406,000
Net Asset (Liability)	$ (3,908,000)	$ (8,848,000)