Derivatives And Risk Management (Derivative Instruments Summary) (Details) - USD ($)	Dec. 31, 2017	Dec. 31, 2016
Derivatives, Fair Value [Line Items]
Asset	$ 51,506,000	$ 61,191,000
Liability	(161,467,000)	(150,381,000)
Collateral Netting	62,408,000	44,758,000
Net Asset (Liability)	(47,553,000)	(44,432,000)
Interest Rate Swap [Member]
Derivatives, Fair Value [Line Items]
Collateral Netting	34,970,000	34,900,000
Collateral Already Posted, Aggregate Fair Value	34,970,000	34,900,000
Commodity Contract [Member]
Derivatives, Fair Value [Line Items]
Collateral Netting	27,438,000	9,858,000
Collateral Already Posted, Aggregate Fair Value	39,458,000	17,134,000
Other Current Liabilities [Member] \| Foreign Currency Exchange Contracts [Member]
Derivatives, Fair Value [Line Items]
Asset		5,000
Liability		(28,000)
Collateral Netting		0
Net Asset (Liability)		(23,000)
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	2,597,000	3,393,000
Liability	(270,000)	0
Collateral Netting	0	0
Net Asset (Liability)	2,327,000	3,393,000
Other Current Assets [Member] \| Commodity Contract [Member]
Derivatives, Fair Value [Line Items]
Asset	1,386,000	18,682,000
Liability	(122,000)	(16,787,000)
Collateral Netting	0	0
Net Asset (Liability)	1,264,000	1,895,000
Current Interest Rate Swap Derivative Liability [Member] \| Interest Rate Swap [Member]
Derivatives, Fair Value [Line Items]
Asset		0
Liability	(63,399,000)	(15,756,000)
Collateral Netting	28,952,000	9,731,000
Net Asset (Liability)	(34,447,000)	(6,025,000)
Non-Current Interest Rate Swap Derivative Liabilities [Member] \| Interest Rate Swap [Member]
Derivatives, Fair Value [Line Items]
Asset		3,951,000
Liability	(7,540,000)	(57,825,000)
Collateral Netting	6,018,000	25,169,000
Net Asset (Liability)	(1,522,000)	(28,705,000)
Current Utility Energy Commodity Derivative Liabilities [Member] \| Commodity Contract [Member]
Derivatives, Fair Value [Line Items]
Asset	26,641,000	16,335,000
Liability	(52,895,000)	(29,598,000)
Collateral Netting	17,406,000	6,228,000
Net Asset (Liability)	(8,848,000)	(7,035,000)
Other Property And Investments Net And Other Non-current Assets [Member] \| Interest Rate Swap [Member]
Derivatives, Fair Value [Line Items]
Asset	4,880,000	5,754,000
Liability	(2,304,000)	(397,000)
Collateral Netting	0	0
Net Asset (Liability)	2,576,000	5,357,000
Other Noncurrent Liabilities [Member] \| Commodity Contract [Member]
Derivatives, Fair Value [Line Items]
Asset	15,970,000	13,071,000
Liability	(34,936,000)	(29,990,000)
Collateral Netting	10,032,000	3,630,000
Net Asset (Liability)	$ (8,934,000)	$ (13,289,000)

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.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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-Section 50
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