Derivative Instruments Gain (Loss) by Hedging Relationship, by Income Statement Location, by Derivative Instrument Risk (details) (USD $)	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012	Dec. 31, 2012
Notional Amount of Derivatives [Abstract]
Derivative, Nonmonetary Notional Amount	30,200,000.0	32,800,000.0	39,500,000.0
Notional Amount of Foreign Currency Derivatives	$ 16,322,000	$ 12,954,000	$ 13,231,000
Summary of Derivative Instruments [Abstract]
Cost of sales	(142,359,000)	(169,755,000)
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 Loss On Derivatives	(200,000)
Derivative Asset, Fair Value, Net	8,300,000
Derivative Liability, Fair Value, Net	1,400,000
Derivative, Loss on Derivative	5,400,000	29,400,000
Derivative Fair Value Of Derivative Net	6,900,000	(55,800,000)	(5,800,000)
Natural Gas Commodity [Member]
Summary of Derivative Instruments [Abstract]
Cost of sales	7,183,000	(55,894,000)
Total Comprehensive Income	0	0
Less:Amounts deferred to regulatory accounts on balance sheet	(7,037,000)	55,894,000
Total gain in pre-tax earnings	146,000	0
Foreign Currency [Member]
Summary of Derivative Instruments [Abstract]
Cost of sales	0	0
Total Comprehensive Income	(239,000)	126,000
Less:Amounts deferred to regulatory accounts on balance sheet	239,000	(126,000)
Total gain in pre-tax earnings	$ 0	$ 0