Derivative Instruments (details) (USD $)	3 Months Ended		9 Months Ended
	Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011	Sep. 30, 2010	Dec. 31, 2010
Summary Of Derivative Instruments Abstract
Cost of sales	$ (43,133,000)	$ (46,359,000)	$ (313,880,000)	$ (281,221,000)
Total Comprehensive Income	(8,166,000)	(7,323,000)	35,092,000	43,369,000
General Discussion Of Derivative Instruments And Hedging Activities Abstract
Changes In Fair Value As Deferred Regulatory Assets Or Liabilities In Percentage			90.00%
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			10.00%
Unrealized Loss On Derivatives	49,900,000		49,900,000
Derivative Loss On Derivative	6,600,000	12,600,000	36,200,000	33,300,000
Derivative Fair Value Of Derivative Net	(49,900,000)	(84,700,000)	(49,900,000)	(84,700,000)	(52,600,000)
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	5,609,000		5,609,000
Without Adequate Assurance Calls	4,581,000		4,581,000
Speculative [Member]
Description Of Credit Risk Related Contingent Features Abstract
With Adequate Assurance Calls	37,171,000		37,171,000
Without Adequate Assurance Calls	31,143,000		31,143,000
Natural Gas Commodity [Member]
Summary Of Derivative Instruments Abstract
Cost of sales	(18,987,000)	(35,744,000)	(49,106,000)	(84,837,000)
Total Comprehensive Income	0	0	0	0
Less:Amounts deferred to regulatory accounts on balance sheet	18,987,000	35,744,000	49,106,000	84,837,000
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	(1,221,000)	449,000	(815,000)	110,000
Less:Amounts deferred to regulatory accounts on balance sheet	1,221,000	(449,000)	815,000	(110,000)
Total Impact On Earnings	$ 0	$ 0	$ 0	$ 0