Derivative Instruments Gain (Loss) by Hedging Relationship, by Income Statement Location, by Derivative Instrument Risk (Details) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015 USD ($)	Sep. 30, 2014 USD ($)	Sep. 30, 2015 USD ($)	Sep. 30, 2014 USD ($)	Dec. 31, 2014 USD ($)
Derivative Instrument Detail [Abstract]
Derivative, Gain on Derivative		$ 500		$ 13,300
Document Period End Date			Sep. 30, 2015
Derivative, Loss on Derivative	$ 2,300		$ 24,300
Unrealized loss On Derivatives	(23,800)		(23,800)
Derivative Asset, Fair Value, Net	3,100	4,000	3,100	4,000	$ 200
Derivative Liability, Fair Value, Net	25,300	3,900	25,300	3,900	33,400
Derivative Fair Value, Net	$ (22,200)	$ 100	$ (22,200)	$ 100	$ (33,200)
Derivative [Line Items]
Financial Derivative, Nonmonetary Notional Amount	4,000	4,000	4,000	4,000	3,000
Physical Derivative, Nonmonetary Notional Amount	5,000	6,000	5,000	6,000	4,000
Notional Amount of Derivatives [Abstract]
Derivative, Notional Amount	$ 0	$ 0	$ 0	$ 0	$ 0
Cost of Revenue	$ 35,856	$ 32,227	$ 223,737	245,708
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			20% or 10%
Oregon PGA Deferral Percentage	80.00%	90.00%
Target Hedge Percentage			approximately 75%
Moody's, A3 Rating [Member]
Derivative [Line Items]
With Adequate Assurance Calls	$ 0		$ 0
Notional Amount of Derivatives [Abstract]
Without Adequate Assurance Calls	0		0
Moody's, Baa1 Rating [Member]
Derivative [Line Items]
With Adequate Assurance Calls	0		0
Notional Amount of Derivatives [Abstract]
Without Adequate Assurance Calls	0		0
Moody's, Baa2 Rating [Member]
Derivative [Line Items]
With Adequate Assurance Calls	0		0
Notional Amount of Derivatives [Abstract]
Without Adequate Assurance Calls	0		0
Moody's, Baa3 Rating [Member]
Derivative [Line Items]
With Adequate Assurance Calls	0		0
Notional Amount of Derivatives [Abstract]
Without Adequate Assurance Calls	0		0
Speculative [Member]
Derivative [Line Items]
With Adequate Assurance Calls	22,066		22,066
Notional Amount of Derivatives [Abstract]
Without Adequate Assurance Calls	15,937		15,937
Natural Gas Commodity [Member]
Notional Amount of Derivatives [Abstract]
Less:Amounts deferred to regulatory accounts on balance sheet	8,391	$ 10,559	21,838	(93)
Total gain (loss) in pre-tax earnings	9	386	17	267
Natural Gas Commodity [Member] | Utility Segment [Member]
Notional Amount of Derivatives [Abstract]
Cost of Revenue	(8,415)	(10,173)	(21,876)	360
Natural Gas Commodity [Member] | Gas Storage Segment [Member]
Notional Amount of Derivatives [Abstract]
Cost of Revenue	33	0	55	0
Foreign Currency [Member]
Notional Amount of Derivatives [Abstract]
Less:Amounts deferred to regulatory accounts on balance sheet	150	421	413	242
Total gain (loss) in pre-tax earnings	0	0	0	0
Foreign Currency [Member] | Utility Segment [Member]
Notional Amount of Derivatives [Abstract]
Cost of Revenue	(150)	(421)	(413)	(242)
Foreign Currency [Member] | Gas Storage Segment [Member]
Notional Amount of Derivatives [Abstract]
Cost of Revenue	$ 0	$ 0	$ 0	$ 0