Derivative Instruments Gain (Loss) by Hedging Relationship, by Income Statement Location, by Derivative Instrument Risk (details) (USD $)	3 Months Ended				9 Months Ended
	Sep. 30, 2012		Sep. 30, 2011		Sep. 30, 2012		Sep. 30, 2011		Dec. 31, 2011
Summary of Derivative Instruments [Abstract]
Cost of sales	$ (37,586,000)		$ (43,133,000)		$ (241,869,000)		$ (313,880,000)
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	5,400,000				5,400,000
Derivative, Loss on Derivative	12,700,000		6,600,000		63,300,000		36,200,000
Derivative Fair Value Of Derivative Net	(5,400,000)		(49,900,000)		(5,400,000)		(49,900,000)		(61,000,000)
Natural Gas Commodity [Member]
Summary of Derivative Instruments [Abstract]
Cost of sales	22,558,000	[1]	(18,987,000)	[1]	(5,556,000)	[1]	(49,106,000)	[1]
Total Comprehensive Income	0	[1]	0	[1]	0	[1]	0	[1]
Less:Amounts deferred to regulatory accounts on balance sheet	(22,558,000)	[1]	18,987,000	[1]	5,556,000	[1]	49,106,000	[1]
Total Impact On Earnings	0	[1]	0	[1]	0	[1]	0	[1]
Foreign Currency [Member]
Summary of Derivative Instruments [Abstract]
Cost of sales	0	[2]	0	[2]	0	[2]	0	[2]
Total Comprehensive Income	273,000	[2]	(1,221,000)	[2]	162,000	[2]	(815,000)	[2]
Less:Amounts deferred to regulatory accounts on balance sheet	(273,000)	[2]	1,221,000	[2]	(162,000)	[2]	815,000	[2]
Total Impact On Earnings	$ 0	[2]	$ 0	[2]	$ 0	[2]	$ 0	[2]

[1] Unrealized gain (loss) from natural gas commodity hedge contracts is recorded in cost of sales and reclassified to regulatory deferral accounts on the balance sheet.

[2] Unrealized gain (loss) from foreign currency exchange contracts is recorded in other comprehensive income, and reclassified to regulatory deferral accounts on the balance sheet.