Derivative Instruments Gain (Loss) by Hedging Relationship, by Income Statement Location, by Derivative Instrument Risk (details) (USD $)	12 Months Ended
	Dec. 31, 2012		Dec. 31, 2011		Dec. 31, 2010
Summary of Derivative Instruments [Abstract]
Cost of sales	$ (355,335,000)		$ (458,508,000)		$ (424,494,000)
General Discussion of Derivative Instruments and Hedging Activities [Abstract]
Changes In Fair Value As Deferred Regulatory Assets Or Liabilities In Percentage	80% or 90%
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%
Unrealized Gain on Foreign Currency Derivatives, before Tax	100,000
Unrealized Loss On Derivatives	5,800,000
Derivative, Loss on Derivative	70,200,000		56,500,000
Maturity Of Credit Risk Derivatives 1	February 2016
Derivative Fair Value Of Derivative Net	(5,800,000)		(61,000,000)
Notional Amount of Derivatives [Abstract]
Derivative, Nonmonetary Notional Amount	39,500,000		35,900,000
Notional Amount of Foreign Currency Derivatives	13,231,000		12,313,000
Natural Gas Commodity [Member]
Summary of Derivative Instruments [Abstract]
Cost of sales	(5,850,000)		(60,799,000)
Total Comprehensive Income	0		0
Less:Amounts deferred to regulatory accounts on balance sheet	5,850,000		60,799,000
Total Impact On Earnings	0	[1]	0	[1]
Foreign Currency [Member]
Summary of Derivative Instruments [Abstract]
Cost of sales	0		0
Total Comprehensive Income	65,000		(201,000)
Less:Amounts deferred to regulatory accounts on balance sheet	(65,000)		201,000
Total Impact On Earnings	$ 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 exchange forward purchase contracts is recorded in other comprehensive income, and reclassified to regulatory deferral accounts on the balance sheet.