Derivative Instruments (details) (USD $)	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Summary Of Derivative Instruments Abstract
Cost of sales	$ (458,622,000)	$ (424,534,000)	$ (611,168,000)
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 Foreign Currency Derivatives, before Tax	200,000
Unrealized Loss On Derivatives	63,500,000
Derivative Loss On Derivative	56,500,000	61,000,000
Maturity Of Credit Risk Derivatives 1	October 2013
Derivative Fair Value Of Derivative Net	(61,000,000)	(52,600,000)
Natural Gas Commodity [Member]
Summary Of Derivative Instruments Abstract
Cost of sales	60,799,000	52,677,000
Total Comprehensive Income	0	0
Less:Amounts deferred to regulatory accounts on balance sheet	60,799,000	52,677,000
Total Impact On Earnings	0	0
Foreign Currency [Member]
Summary Of Derivative Instruments Abstract
Cost of sales	0	0
Total Comprehensive Income	(201,000)	91,000
Less:Amounts deferred to regulatory accounts on balance sheet	201,000	(91,000)
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	2,013,000
Without Adequate Assurance Calls	851,000
Moodys Baa 3 Rating [Member]
Description Of Credit Risk Related Contingent Features Abstract
With Adequate Assurance Calls	9,585,000
Without Adequate Assurance Calls	5,923,000
Speculative [Member]
Description Of Credit Risk Related Contingent Features Abstract
With Adequate Assurance Calls	45,869,000
Without Adequate Assurance Calls	$ 37,206,000