Segment Information (Details) $ in Thousands		3 Months Ended		9 Months Ended
		Sep. 30, 2016 USD ($)	Sep. 30, 2015 USD ($)	Sep. 30, 2016 USD ($)	Sep. 30, 2015 USD ($)	Dec. 31, 2015 USD ($)
Segment Reporting Information [Line Items]
Operating revenues		$ 87,727	$ 93,128	$ 442,439	$ 493,073
Cost of Gas		28,264	35,856	157,546	223,737
Environmental Remediation Expense		1,191	0	8,113	0
Depreciation and amortization		20,628	20,342	61,435	60,683
Income from operations		(4,437)	(1,873)	82,241	64,042
Net Income		(8,040)	(6,685)	30,620	23,998
Capital expenditures		36,675	28,851	98,111	86,923
Assets		2,959,884	2,970,718	$ 2,959,884	2,970,718	$ 3,069,410
Operating Segments [Member]
Segment Reporting Information [Line Items]
Number of Reportable Segments				2
Operating Segments [Member] | Utility Segment [Member]
Segment Reporting Information [Line Items]
Operating revenues	[1]	80,378	87,475	$ 422,617	476,672
Cost of Gas		28,264	35,856	157,546	223,737
Environmental Remediation Expense		1,191	0	8,113	0
Gross Profit		50,923	51,619	256,958	252,935
Depreciation and amortization		19,173	18,721	56,894	55,798
Income from operations		(7,264)	(4,088)	74,745	59,955
Net Income		(9,511)	(7,529)	26,848	23,051
Capital expenditures		36,238	28,325	96,710	84,598
Assets		2,684,618	2,686,367	2,684,618	2,686,367	2,792,736
Operating Segments [Member] | Gas Storage Segment [Member]
Segment Reporting Information [Line Items]
Operating revenues		7,293	5,596	19,654	16,232
Depreciation and amortization		1,455	1,621	4,541	4,885
Income from operations		3,502	2,204	8,107	3,998
Net Income		1,813	799	3,988	827
Capital expenditures		437	526	1,401	2,325
Assets		259,483	269,228	259,483	269,228	261,750
Operating Segments [Member] | Corporate, Non-Segment [Member]
Segment Reporting Information [Line Items]
Operating revenues		56	57	168	169
Depreciation and amortization		0	0	0	0
Income from operations		(675)	11	(611)	89
Net Income		(342)	45	(216)	120
Capital expenditures		0	0	0	0
Assets		$ 15,783	$ 15,123	$ 15,783	$ 15,123	$ 14,924

[1] Utility operating revenues include environmental recovery revenues, which are collections received from customers through our environmental recovery mechanism in Oregon, offset by environmental remediation expense. Collections under this mechanism began in November 2015.