Derivative Instruments Gain (Loss) by Hedging Relationship, by Income Statement Location, by Derivative Instrument Risk (details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013	Dec. 31, 2013
Derivative [Line Items]
Financial Derivative, Nonmonetary Notional Amount	368,425	527,700	368,425	527,700	389,000
Physical Derivative, Nonmonetary Notional Amount	620,550	572,675	620,550	572,675	552,500
Derivative, Notional Amount	$ 10,296	$ 13,862	$ 10,296	$ 13,862	$ 15,002
Summary of Derivative Instruments [Abstract]
Cost of sales	(32,227)	(33,655)	(245,708)	(235,156)
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%
Oregon PGA Deferral Percentage	90.00%	90.00%
Target Hedge Percentage			approximately 75%
Derivative, Gain on Derivative	500		13,300
Derivative, Loss on Derivative		2,300		6,300
Unrealized Gain On Derivatives	1,700		1,700
Derivative Asset, Fair Value, Net	4,000	200	4,000	200	7,200
Derivative Liability, Fair Value, Net	3,900	6,700	3,900	6,700	2,500
Derivative Fair Value, Net	100	6,500	100	6,500	4,700
Natural Gas Commodity [Member]
Summary of Derivative Instruments [Abstract]
Cost of sales	(10,173)	2,422	360	(6,534)
Less:Amounts deferred to regulatory accounts on balance sheet	(10,559)	2,433	93	(6,599)
Total gain (loss) in pre-tax earnings	386	(11)	267	65
Foreign Currency [Member]
Summary of Derivative Instruments [Abstract]
Cost of sales	(421)	502	242	11
Less:Amounts deferred to regulatory accounts on balance sheet	(421)	502	242	11
Total gain (loss) in pre-tax earnings	$ 0	$ 0	$ 0	$ 0