Derivative Instruments (details) (USD $)	3 Months Ended		6 Months Ended
	Jun. 30, 2011	Jun. 30, 2010	Jun. 30, 2011	Jun. 30, 2010	Dec. 31, 2010
Summary Of Derivative Instruments Abstract
Cost of sales	$ (90,122,000)	$ (86,301,000)	$ (270,747,000)	$ (234,862,000)
Total Comprehensive Income	2,339,000	6,986,000	43,258,000	50,692,000
General Discussion Of Derivative Instruments And Hedging Activities Abstract
Date Of Annual Purchase Gas Agreement Set Price	November 1, 2010		November 1, 2010
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%
Counterparty Credit Limit Range Minimum	25,000,000		25,000,000
Counterparty Credit Limit Range Maximum	50,000,000		50,000,000
Unrealized Loss On Derivatives	29,700,000		29,700,000
Derivative Loss On Derivative	8,700,000	14,600,000	29,600,000	20,800,000
Derivative Fair Value Of Derivative Net	(29,700,000)	(49,400,000)	(29,700,000)	(49,400,000)	(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	1,966,000		1,966,000
Without Adequate Assurance Calls	1,966,000		1,966,000
Speculative [Member]
Description Of Credit Risk Related Contingent Features Abstract
With Adequate Assurance Calls	16,900,000		16,900,000
Without Adequate Assurance Calls	13,892,000		13,892,000
Natural Gas Commodity [Member]
Summary Of Derivative Instruments Abstract
Cost of sales	3,631,000	8,471,000	(30,119,000)	(49,093,000)
Total Comprehensive Income	0	0	0	0
Less:Amounts deferred to regulatory accounts on balance sheet	(3,631,000)	(8,471,000)	30,119,000	49,093,000
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	(196,000)	(356,000)	406,000	(339,000)
Less:Amounts deferred to regulatory accounts on balance sheet	196,000	356,000	(406,000)	339,000
Total Impact On Earnings	$ 0	$ 0	$ 0	$ 0