Derivatives And Risk Management (Derivative Instruments Summary) (Details) - USD ($)	Mar. 31, 2017	Dec. 31, 2016
Derivatives, Fair Value [Line Items]
Gross Asset	$ 63,572,000	$ 61,191,000
Gross Liability	(144,287,000)	(150,381,000)
Collateral Netted	43,683,000	44,758,000
Net Asset (Liability) on Balance Sheet	(37,032,000)	(44,432,000)
Interest Rate Swap [Member]
Derivatives, Fair Value [Line Items]
Collateral Netted	36,140,000	34,900,000
Commodity Contracts [Member]
Derivatives, Fair Value [Line Items]
Collateral Netted	7,543,000	9,858,000
Other Current Assets [Member] | Foreign Exchange Contract [Member]
Derivatives, Fair Value [Line Items]
Gross Asset	37,000
Gross Liability	0
Collateral Netted	0
Net Asset (Liability) on Balance Sheet	37,000
Other Current Assets [Member] | Interest Rate Swap [Member]
Derivatives, Fair Value [Line Items]
Gross Asset	3,748,000	3,393,000
Gross Liability	0	0
Collateral Netted	0	0
Net Asset (Liability) on Balance Sheet	3,748,000	3,393,000
Other Current Assets [Member] | Commodity Contracts [Member]
Derivatives, Fair Value [Line Items]
Gross Asset	604,000	18,682,000
Gross Liability	(47,000)	(16,787,000)
Collateral Netted	0	0
Net Asset (Liability) on Balance Sheet	557,000	1,895,000
Other Current Liabilities [Member] | Foreign Exchange Contract [Member]
Derivatives, Fair Value [Line Items]
Gross Asset		5,000
Gross Liability		(28,000)
Collateral Netted		0
Net Asset (Liability) on Balance Sheet		(23,000)
Other Current Liabilities [Member] | Interest Rate Swap [Member]
Derivatives, Fair Value [Line Items]
Gross Asset	0	0
Gross Liability	(15,069,000)	(15,756,000)
Collateral Netted	10,100,000	9,731,000
Net Asset (Liability) on Balance Sheet	(4,969,000)	(6,025,000)
Non-Current Interest Rate Swap Derivative Liabilities [Member] | Interest Rate Swap [Member]
Derivatives, Fair Value [Line Items]
Gross Asset	5,078,000	3,951,000
Gross Liability	(54,261,000)	(57,825,000)
Collateral Netted	26,040,000	25,169,000
Net Asset (Liability) on Balance Sheet	(23,143,000)	(28,705,000)
Other Property And Investments Net and Other Non-current Assets[Member] | Interest Rate Swap [Member]
Derivatives, Fair Value [Line Items]
Gross Asset	6,754,000	5,754,000
Gross Liability	(116,000)	(397,000)
Collateral Netted	0	0
Net Asset (Liability) on Balance Sheet	6,638,000	5,357,000
Current Utility Energy Commodity Derivative Liabilities [Member] | Commodity Contracts [Member]
Derivatives, Fair Value [Line Items]
Gross Asset	29,929,000	16,335,000
Gross Liability	(42,136,000)	(29,598,000)
Collateral Netted	4,726,000	6,228,000
Net Asset (Liability) on Balance Sheet	(7,481,000)	(7,035,000)
Other Noncurrent Liabilities [Member] | Commodity Contracts [Member]
Derivatives, Fair Value [Line Items]
Gross Asset	17,422,000	13,071,000
Gross Liability	(32,658,000)	(29,990,000)
Collateral Netted	2,817,000	3,630,000
Net Asset (Liability) on Balance Sheet	$ (12,419,000)	$ (13,289,000)