Derivatives And Risk Management (Derivative Instruments Summary) (Details) - USD ($)	Mar. 31, 2018	Dec. 31, 2017
Derivatives, Fair Value [Line Items]
Gross Asset	$ 74,809,000	$ 51,506,000
Gross Liability	(145,975,000)	(161,467,000)
Collateral Netted	44,226,000	62,408,000
Net Asset (Liability) on Balance Sheet	(26,940,000)	(47,553,000)
Interest Rate Swap [Member]
Derivatives, Fair Value [Line Items]
Collateral Netted	27,630,000	34,970,000
Commodity Contracts [Member]
Derivatives, Fair Value [Line Items]
Collateral Netted	16,596,000	27,438,000
Other Current Assets [Member] | Foreign Exchange Contract [Member]
Derivatives, Fair Value [Line Items]
Gross Asset	22,000	32,000
Gross Liability	(6,000)	(1,000)
Collateral Netted	0	0
Net Asset (Liability) on Balance Sheet	16,000	31,000
Other Current Assets [Member] | Interest Rate Swap [Member]
Derivatives, Fair Value [Line Items]
Gross Asset	3,930,000	2,597,000
Gross Liability	0	(270,000)
Collateral Netted	0	0
Net Asset (Liability) on Balance Sheet	3,930,000	2,327,000
Other Current Assets [Member] | Commodity Contracts [Member]
Derivatives, Fair Value [Line Items]
Gross Asset	995,000	1,386,000
Gross Liability	(34,000)	(122,000)
Collateral Netted	0	0
Net Asset (Liability) on Balance Sheet	961,000	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	9,512,000	4,880,000
Gross Liability	(358,000)	(2,304,000)
Collateral Netted	0	0
Net Asset (Liability) on Balance Sheet	9,154,000	2,576,000
Other Current Liabilities [Member] | Interest Rate Swap [Member]
Derivatives, Fair Value [Line Items]
Gross Asset	1,273,000	0
Gross Liability	(49,052,000)	(63,399,000)
Collateral Netted	22,693,000	28,952,000
Net Asset (Liability) on Balance Sheet	(25,086,000)	(34,447,000)
Current Utility Energy Commodity Derivative Liabilities [Member] | Commodity Contracts [Member]
Derivatives, Fair Value [Line Items]
Gross Asset	39,944,000	26,641,000
Gross Liability	(61,978,000)	(52,895,000)
Collateral Netted	12,274,000	17,406,000
Net Asset (Liability) on Balance Sheet	(9,760,000)	(8,848,000)
Other Noncurrent Liabilities [Member] | Interest Rate Swap [Member]
Derivatives, Fair Value [Line Items]
Gross Asset	0	0
Gross Liability	(6,321,000)	(7,540,000)
Collateral Netted	4,937,000	6,018,000
Net Asset (Liability) on Balance Sheet	(1,384,000)	(1,522,000)
Other Noncurrent Liabilities [Member] | Commodity Contracts [Member]
Derivatives, Fair Value [Line Items]
Gross Asset	19,133,000	15,970,000
Gross Liability	(28,226,000)	(34,936,000)
Collateral Netted	4,322,000	10,032,000
Net Asset (Liability) on Balance Sheet	$ (4,771,000)	$ (8,934,000)