Derivatives And Risk Management (Derivative Instruments Summary) (Details) - USD ($)	Sep. 30, 2018	Dec. 31, 2017
Derivatives, Fair Value [Line Items]
Gross Asset	$ 55,941,000	$ 51,506,000
Gross Liability	(71,127,000)	(161,467,000)
Collateral Netted	19,349,000	62,408,000
Net Asset (Liability) on Balance Sheet	4,163,000	(47,553,000)
Interest Rate Swap [Member]
Derivatives, Fair Value [Line Items]
Collateral Netted	0	34,970,000
Commodity Contracts [Member]
Derivatives, Fair Value [Line Items]
Collateral Netted	19,349,000	27,438,000
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	29,992,000	26,641,000
Gross Liability	(50,107,000)	(52,895,000)
Collateral Netted	13,262,000	17,406,000
Net Asset (Liability) on Balance Sheet	(6,853,000)	(8,848,000)
Other Current Assets [Member] | Foreign Exchange Contract [Member]
Derivatives, Fair Value [Line Items]
Gross Asset	26,000	32,000
Gross Liability	0	(1,000)
Collateral Netted	0	0
Net Asset (Liability) on Balance Sheet	26,000	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	904,000	1,386,000
Gross Liability	(27,000)	(122,000)
Collateral Netted	0	0
Net Asset (Liability) on Balance Sheet	877,000	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	18,029,000	4,880,000
Gross Liability	0	(2,304,000)
Collateral Netted	0	0
Net Asset (Liability) on Balance Sheet	18,029,000	2,576,000
Other Property And Investments Net And Other Non-current Assets [Member] | Commodity Contracts [Member]
Derivatives, Fair Value [Line Items]
Gross Asset	7,000
Gross Liability	0
Collateral Netted	0
Net Asset (Liability) on Balance Sheet	7,000
Other Noncurrent Liabilities [Member] | Interest Rate Swap [Member]
Derivatives, Fair Value [Line Items]
Gross Asset	129,000	0
Gross Liability	(4,577,000)	(7,540,000)
Collateral Netted	0	6,018,000
Net Asset (Liability) on Balance Sheet	(4,448,000)	(1,522,000)
Other Noncurrent Liabilities [Member] | Commodity Contracts [Member]
Derivatives, Fair Value [Line Items]
Gross Asset	6,854,000	15,970,000
Gross Liability	(16,416,000)	(34,936,000)
Collateral Netted	6,087,000	10,032,000
Net Asset (Liability) on Balance Sheet	$ (3,475,000)	$ (8,934,000)