Derivatives And Risk Management (Derivative Instruments Summary) (Details) - USD ($)	Jun. 30, 2018	Dec. 31, 2017
Derivatives, Fair Value [Line Items]
Gross Asset	$ 55,291,000	$ 51,506,000
Gross Liability	(81,500,000)	(161,467,000)
Collateral Netted	22,371,000	62,408,000
Net Asset (Liability) on Balance Sheet	(3,838,000)	(47,553,000)
Interest Rate Swap [Member]
Derivatives, Fair Value [Line Items]
Collateral Netted	590,000	34,970,000
Commodity Contracts [Member]
Derivatives, Fair Value [Line Items]
Collateral Netted	21,781,000	27,438,000
Other Current Liabilities [Member] \| Foreign Exchange Contract [Member]
Derivatives, Fair Value [Line Items]
Gross Asset	16,000
Gross Liability	(21,000)
Collateral Netted	0
Net Asset (Liability) on Balance Sheet	(5,000)
Other Current Liabilities [Member] \| Interest Rate Swap [Member]
Derivatives, Fair Value [Line Items]
Gross Asset		0
Gross Liability		(63,399,000)
Collateral Netted		28,952,000
Net Asset (Liability) on Balance Sheet		(34,447,000)
Other Current Liabilities [Member] \| Commodity Contracts [Member]
Derivatives, Fair Value [Line Items]
Gross Asset	32,292,000	26,641,000
Gross Liability	(54,138,000)	(52,895,000)
Collateral Netted	14,057,000	17,406,000
Net Asset (Liability) on Balance Sheet	(7,789,000)	(8,848,000)
Other Current Assets [Member] \| Foreign Exchange Contract [Member]
Derivatives, Fair Value [Line Items]
Gross Asset		32,000
Gross Liability		(1,000)
Collateral Netted		0
Net Asset (Liability) on Balance Sheet		31,000
Other Current Assets [Member] \| Interest Rate Swap [Member]
Derivatives, Fair Value [Line Items]
Gross Asset		2,597,000
Gross Liability		(270,000)
Collateral Netted		0
Net Asset (Liability) on Balance Sheet		2,327,000
Other Current Assets [Member] \| Commodity Contracts [Member]
Derivatives, Fair Value [Line Items]
Gross Asset	96,000	1,386,000
Gross Liability	0	(122,000)
Collateral Netted	0	0
Net Asset (Liability) on Balance Sheet	96,000	1,264,000
Other Property And Investments Net And Other Non-current Assets [Member] \| Interest Rate Swap [Member]
Derivatives, Fair Value [Line Items]
Gross Asset	12,314,000	4,880,000
Gross Liability	0	(2,304,000)
Collateral Netted	0	0
Net Asset (Liability) on Balance Sheet	12,314,000	2,576,000
Other Property And Investments Net And Other Non-current Assets [Member] \| Commodity Contracts [Member]
Derivatives, Fair Value [Line Items]
Gross Asset	15,000
Gross Liability	0
Collateral Netted	0
Net Asset (Liability) on Balance Sheet	15,000
Other Noncurrent Liabilities [Member] \| Interest Rate Swap [Member]
Derivatives, Fair Value [Line Items]
Gross Asset	0	0
Gross Liability	(5,491,000)	(7,540,000)
Collateral Netted	590,000	6,018,000
Net Asset (Liability) on Balance Sheet	(4,901,000)	(1,522,000)
Other Noncurrent Liabilities [Member] \| Commodity Contracts [Member]
Derivatives, Fair Value [Line Items]
Gross Asset	10,558,000	15,970,000
Gross Liability	(21,850,000)	(34,936,000)
Collateral Netted	7,724,000	10,032,000
Net Asset (Liability) on Balance Sheet	$ (3,568,000)	$ (8,934,000)

Fair values as of the balance sheet date of the net amount of all assets and liabilities resulting from contracts that meet the criteria of being accounted for as derivative instruments.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 45
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=6945355&loc=d3e41228-113958

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