Derivative Instruments (details) (USD $)	3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011	Dec. 31, 2011
Summary Of Derivative Instruments Abstract
Cost of sales	$ (169,771,000)	$ (180,625,000)
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	55,800,000
Derivative Loss On Derivative	29,400,000	20,900,000
Derivative Fair Value Of Derivative Net	(55,800,000)	(33,100,000)	(61,000,000)
Natural Gas Commodity [Member]
Summary Of Derivative Instruments Abstract
Cost of sales	(55,894,000)	(33,750,000)
Total Comprehensive Income	0	0
Less:Amounts deferred to regulatory accounts on balance sheet	55,894,000	33,750,000
Total Impact On Earnings	0	0
Foreign Currency [Member]
Summary Of Derivative Instruments Abstract
Cost of sales	0	0
Total Comprehensive Income	126,000	602,000
Less:Amounts deferred to regulatory accounts on balance sheet	(126,000)	(602,000)
Total Impact On Earnings	0	0
Moodys A3 Rating [Member]
Description Of Credit Risk Related Contingent Features Abstract
With Adequate Assurance Calls	0
Without Adequate Assurance Calls	0
Moodys Baa 1 Rating [Member]
Description Of Credit Risk Related Contingent Features Abstract
With Adequate Assurance Calls	0
Without Adequate Assurance Calls	0
Moodys Baa 2 Rating [Member]
Description Of Credit Risk Related Contingent Features Abstract
With Adequate Assurance Calls	12,785,000
Without Adequate Assurance Calls	0
Moodys Baa 3 Rating [Member]
Description Of Credit Risk Related Contingent Features Abstract
With Adequate Assurance Calls	6,805,000
Without Adequate Assurance Calls	4,292,000
Speculative [Member]
Description Of Credit Risk Related Contingent Features Abstract
With Adequate Assurance Calls	40,441,000
Without Adequate Assurance Calls	$ 32,928,000