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, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Dec. 31, 2012
Notional Amount of Derivatives [Abstract]
Derivative, Nonmonetary Notional Amount	527,700,000	460,470,000	527,700,000	460,470,000	395,820,000
Notional Amount of Foreign Currency Derivatives	$ 13,862,000	$ 13,775,000	$ 13,862,000	$ 13,775,000	$ 13,231,000
Summary of Derivative Instruments [Abstract]
Cost of sales	(33,655,000)	(37,570,000)	(235,156,000)	(241,823,000)
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%
Target Hedge Percentage			approximately 75%
Unrealized Loss On Derivatives	6,400,000		6,400,000
Derivative Asset, Fair Value, Net	200,000	200,000	200,000	200,000
Derivative Liability, Fair Value, Net	6,700,000	5,600,000	6,700,000	5,600,000
Derivative, Loss on Derivative	2,300,000	12,700,000	6,300,000	63,300,000
Derivative Fair Value Of Derivative Net	(6,500,000)	(5,400,000)	(6,500,000)	(5,400,000)	(5,800,000)
Natural Gas Commodity [Member]
Summary of Derivative Instruments [Abstract]
Cost of sales	2,422,000	22,558,000	(6,534,000)	(5,556,000)
Other comprehensive loss	0	0	0	0
Less:Amounts deferred to regulatory accounts on balance sheet	(2,433,000)	(22,558,000)	6,599,000	5,556,000
Total gain (loss) in pre-tax earnings	(11,000)	0	65,000	0
Foreign Currency [Member]
Summary of Derivative Instruments [Abstract]
Cost of sales	0	0	0	0
Other comprehensive loss	502,000	273,000	(11,000)	162,000
Less:Amounts deferred to regulatory accounts on balance sheet	(502,000)	(273,000)	11,000	(162,000)
Total gain (loss) in pre-tax earnings	$ 0	$ 0	$ 0	$ 0