Derivative Instruments Gain (Loss) by Hedging Relationship, by Income Statement Location, by Derivative Instrument Risk (details) (USD $)	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012	Dec. 31, 2012
Notional Amount of Derivatives [Abstract]
Derivative, Nonmonetary Notional Amount	35,900,000.0	35,100,000.0	35,900,000.0	35,100,000.0	39,500,000.0
Notional Amount of Foreign Currency Derivatives	$ 17,171,000	$ 13,725,000	$ 17,171,000	$ 13,725,000	$ 13,231,000
Summary of Derivative Instruments [Abstract]
Cost of sales	(59,142,000)	(34,498,000)	(201,501,000)	(204,253,000)
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	8,800,000		8,800,000
Derivative Asset, Fair Value, Net	200,000	900,000	200,000	900,000
Derivative Liability, Fair Value, Net	9,700,000	29,100,000	9,700,000	29,100,000
Derivative, Gain on Derivative	1,400,000
Derivative, Loss on Derivative		21,300,000	4,000,000	50,700,000
Derivative Fair Value Of Derivative Net	(9,500,000)	(28,200,000)	(9,500,000)	(28,200,000)	(5,800,000)
Natural Gas Commodity [Member]
Summary of Derivative Instruments [Abstract]
Cost of sales	(16,139,000)	27,780,000	(8,956,000)	(28,114,000)
Other comprehensive loss	0	0	0	0
Less:Amounts deferred to regulatory accounts on balance sheet	16,069,000	(27,780,000)	9,032,000	28,114,000
Total gain (loss) in pre-tax earnings	(70,000)	0	76,000	0
Foreign Currency [Member]
Summary of Derivative Instruments [Abstract]
Cost of sales	0	0	0	0
Other comprehensive loss	(274,000)	(237,000)	(513,000)	(111,000)
Less:Amounts deferred to regulatory accounts on balance sheet	274,000	237,000	513,000	111,000
Total gain (loss) in pre-tax earnings	$ 0	$ 0	$ 0	$ 0