Derivative Instruments (details) (USD $)	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011	Dec. 31, 2011
Summary Of Derivative Instruments Abstract
Cost of sales	$ (34,512,000)	$ (90,122,000)	$ (204,283,000)	$ (270,747,000)
General Discussion Of Derivative Instruments And Hedging Activities Abstract
Changes In Fair Value As Deferred Regulatory Assets Or Liabilities In Percentage			80 or a 90 percent
Changes In Fair Value Deferred As Income Statement For Contracts Not Qualifying For Hedge Accounting And To Other Comprehensive Income For Contracts Qualifying For Hedge Accounting			10 or 20 percent
Unrealized Loss On Derivatives	28,200,000		28,200,000
Derivative Loss On Derivative	21,300,000	8,700,000	50,700,000	29,600,000
Derivative Fair Value Of Derivative Net	(28,200,000)	(29,700,000)	(28,200,000)	(29,700,000)	(61,000,000)
Natural Gas Commodity [Member]
Summary Of Derivative Instruments Abstract
Cost of sales	27,780,000	3,631,000	(28,114,000)	(30,119,000)
Total Comprehensive Income	0	0	0	0
Less:Amounts deferred to regulatory accounts on balance sheet	(27,780,000)	(3,631,000)	28,114,000	30,119,000
Total Impact On Earnings	0	0	0	0
Foreign Currency [Member]
Summary Of Derivative Instruments Abstract
Cost of sales	0	0	0	0
Total Comprehensive Income	(237,000)	(196,000)	(111,000)	406,000
Less:Amounts deferred to regulatory accounts on balance sheet	237,000	196,000	111,000	(406,000)
Total Impact On Earnings	0	0	0	0
Moodys A3 Rating [Member]
Description Of Credit Risk Related Contingent Features Abstract
With Adequate Assurance Calls	0		0
Without Adequate Assurance Calls	0		0
Moodys Baa 1 Rating [Member]
Description Of Credit Risk Related Contingent Features Abstract
With Adequate Assurance Calls	0		0
Without Adequate Assurance Calls	0		0
Moodys Baa 2 Rating [Member]
Description Of Credit Risk Related Contingent Features Abstract
With Adequate Assurance Calls	0		0
Without Adequate Assurance Calls	0		0
Moodys Baa 3 Rating [Member]
Description Of Credit Risk Related Contingent Features Abstract
With Adequate Assurance Calls	0		0
Without Adequate Assurance Calls	0		0
Speculative [Member]
Description Of Credit Risk Related Contingent Features Abstract
With Adequate Assurance Calls	15,342,000		15,342,000
Without Adequate Assurance Calls	$ 19,222,000		$ 19,222,000