Segment Information - Schedule of Summarized Financial Information by Segment - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020	Dec. 31, 2020
Segment Reporting Information [Line Items]
Operating revenues	$ 148,917	$ 134,971	$ 464,863	$ 420,122
Depreciation and amortization	28,144	25,836	56,241	50,511
Income from operations	12,624	8,942	107,330	85,388
Income (Loss) from Continuing Operations, Net of Tax, Attributable to Parent	(724)	(5,132)	58,793	43,144
Total assets	3,783,500	3,641,347	3,783,500	3,641,347	$ 3,756,379
Discontinued operations - total assets		16,400		16,400
Natural Gas Distribution [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Operating revenues	139,614	126,992	440,952	405,479
Depreciation and amortization	27,273	24,738	54,186	48,684
Income from operations	11,331	6,434	97,818	81,692
Income (Loss) from Continuing Operations, Net of Tax, Attributable to Parent	(1,381)	(6,347)	52,544	41,596
Capital expenditures	60,376	61,472	124,368	117,629
Total assets	3,587,966	3,470,306	3,587,966	3,470,306	3,549,868
Other Northwest Natural [Member] | Corporate, Non-Segment [Member]
Segment Reporting Information [Line Items]
Operating revenues	4,965	4,165	15,977	8,207
Depreciation and amortization	257	248	513	492
Income from operations	2,808	2,465	11,439	4,228
Income (Loss) from Continuing Operations, Net of Tax, Attributable to Parent	1,970	1,635	8,156	2,871
Capital expenditures	693	521	799	598
Total assets	51,466	10,398	51,466	10,398	49,468
Northwest Natural Gas Company [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Operating revenues	144,579	131,157	456,929	413,686
Depreciation and amortization	27,530	24,986	54,699	49,176
Income from operations	14,139	8,899	109,257	85,920
Income (Loss) from Continuing Operations, Net of Tax, Attributable to Parent	589	(4,712)	60,700	44,467
Capital expenditures	61,069	61,993	125,167	118,227
Total assets	3,639,432	3,480,704	3,639,432	3,480,704	3,599,336
Other Northwest Holdings [Member] | Corporate, Non-Segment [Member]
Segment Reporting Information [Line Items]
Operating revenues	4,338	3,814	7,934	6,436
Depreciation and amortization	614	850	1,542	1,335
Income from operations	(1,515)	43	(1,927)	(532)
Income (Loss) from Continuing Operations, Net of Tax, Attributable to Parent	(1,313)	(420)	(1,907)	(1,323)
Capital expenditures	3,337	2,843	4,941	4,055
Total assets	144,068	144,251	144,068	144,251	157,043
Northwest Natural Gas Company [Member]
Segment Reporting Information [Line Items]
Operating revenues	144,579	131,157	456,929	413,686
Depreciation and amortization	27,530	24,986	54,699	49,176
Income from operations	14,139	8,899	109,257	85,920
Total assets	3,639,432	3,480,704	3,639,432	3,480,704	3,599,336
Northwest Natural Gas Company [Member] | Natural Gas Distribution [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Operating revenues	139,614	126,992	440,952	405,479
Northwest Natural Gas Company [Member] | Other Northwest Natural [Member] | Corporate, Non-Segment [Member]
Segment Reporting Information [Line Items]
Operating revenues	4,965	4,165	15,977	8,207
Northwest Natural Gas Company [Member] | Northwest Natural Gas Company [Member]
Segment Reporting Information [Line Items]
Operating revenues	144,579	131,157	456,929	413,686
Parent Company [Member]
Segment Reporting Information [Line Items]
Operating revenues	148,917	134,971	464,863	420,122
Depreciation and amortization	28,144	25,836	56,241	50,511
Income from operations	12,624	8,942	107,330	85,388
Income (Loss) from Continuing Operations, Net of Tax, Attributable to Parent	(724)	(5,132)	58,793	43,144
Capital expenditures	64,406	64,836	130,108	122,282
Total assets	$ 3,783,500	$ 3,624,955	$ 3,783,500	$ 3,624,955	$ 3,756,379