Consolidated Statements of Comprehensive Income - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Operating revenues [Abstract]
Operating revenues	$ 93,284	$ 90,317	$ 513,406	$ 499,108
Operating expenses:
Cost of gas	23,741	22,603	173,489	163,167
Operations and maintenance	41,352	40,886	134,256	131,854
Environmental remediation	867	967	6,494	7,258
General taxes	8,656	7,993	26,924	24,899
Revenue taxes	3,555	3,534	19,752	19,956
Depreciation and amortization	25,934	23,375	76,445	67,334
Other operating expenses	767	593	2,246	2,131
Total operating expenses	104,872	99,951	439,606	416,599
Income from operations	(11,588)	(9,634)	73,800	82,509
Other income (expense), net	(3,287)	(2,267)	(9,902)	(18,782)
Interest expense, net	9,165	10,948	32,339	31,807
Income (loss) before income taxes	(24,040)	(22,849)	31,559	31,920
Income tax expense (benefit)	(5,363)	(4,343)	7,092	4,957
Net income (loss) from continuing operations	(18,677)	(18,506)	24,467	26,963
Income (loss) from discontinued operations, net of tax	765	(795)	267	(1,968)
Net income (loss)	(17,912)	(19,301)	24,734	24,995
Other comprehensive income:
Amortization of non-qualified employee benefit plan liability, net of taxes	186	114	506	344
Amortization of non-qualified employee benefit plan liability, tax	66	43	182	125
Comprehensive income (loss)	$ (17,726)	$ (19,187)	$ 25,240	$ 25,339
Average common shares outstanding:
Basic (in shares)	30,555	30,429	30,528	29,563
Diluted (in shares)	30,555	30,429	30,575	29,628
Earnings from continuing operations per share of common stock:
Basic (in dollars per share)	$ (0.61)	$ (0.61)	$ 0.80	$ 0.91
Diluted (in dollars per share)	(0.61)	(0.61)	0.80	0.91
Loss from discontinued operations per share of common stock:
Basic (in dollars per share)	0.02	(0.02)	0.01	(0.07)
Diluted (in dollars per share)	0.02	(0.02)	0.01	(0.07)
Earnings (loss) per share of common stock:
Basic (in dollars per share)	(0.59)	(0.63)	0.81	0.84
Diluted (in dollars per share)	$ (0.59)	$ (0.63)	$ 0.81	$ 0.84
Northwest Natural Gas Company [Member]
Operating revenues [Abstract]
Operating revenues	$ 88,367	$ 87,592	$ 502,053	$ 494,680
Operating expenses:
Cost of gas	23,797	22,659	173,657	163,335
Operations and maintenance	38,657	37,710	126,111	125,436
Environmental remediation	867	967	6,494	7,258
General taxes	8,554	7,881	26,564	24,695
Revenue taxes	3,555	3,534	19,752	19,956
Depreciation and amortization	25,681	23,074	74,857	66,821
Other operating expenses	725	586	2,167	2,114
Total operating expenses	101,836	96,411	429,602	409,615
Income from operations	(13,469)	(8,819)	72,451	85,065
Other income (expense), net	(4,002)	(2,323)	(10,744)	(18,905)
Interest expense, net	8,806	10,459	30,518	30,979
Income (loss) before income taxes	(26,277)	(21,601)	31,189	35,181
Income tax expense (benefit)	(6,057)	(4,013)	6,942	5,820
Net income (loss)	(20,220)	(17,588)	24,247	29,361
Other comprehensive income:
Amortization of non-qualified employee benefit plan liability, net of taxes	186	114	506	344
Amortization of non-qualified employee benefit plan liability, tax	66	43	182	125
Comprehensive income (loss)	$ (20,034)	$ (17,474)	$ 24,753	$ 29,705