Segment Information - Schedule of Summarized Financial Information by Segment - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020
Segment Reporting Information [Line Items]
Operating revenues	$ 315,946	$ 285,151
Depreciation and amortization	28,097	24,675
Income from operations	94,706	76,446
Income (Loss) from Continuing Operations, Net of Tax, Attributable to Parent	59,517	48,276
Total assets	3,758,625	4,001,527	$ 3,756,379
Discontinued operations - total assets		15,300
Natural Gas Distribution [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Operating revenues	301,338	278,487
Depreciation and amortization	26,913	23,946
Income from operations	86,487	75,258
Income (Loss) from Continuing Operations, Net of Tax, Attributable to Parent	53,925	47,943
Capital expenditures	63,992	56,157
Total assets	3,570,153	3,776,650	3,549,868
Other Northwest Natural [Member] | Corporate, Non-Segment [Member]
Segment Reporting Information [Line Items]
Operating revenues	11,012	4,042
Depreciation and amortization	256	244
Income from operations	8,631	1,763
Income (Loss) from Continuing Operations, Net of Tax, Attributable to Parent	6,186	1,236
Capital expenditures	106	77
Total assets	49,415	48,746	49,468
Northwest Natural Gas Company [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Operating revenues	312,350	282,529
Depreciation and amortization	27,169	24,190
Income from operations	95,118	77,021
Income (Loss) from Continuing Operations, Net of Tax, Attributable to Parent	60,111	49,179
Capital expenditures	64,098	56,234
Total assets	3,619,568	3,825,396	3,599,336
Other Northwest Holdings [Member] | Corporate, Non-Segment [Member]
Segment Reporting Information [Line Items]
Operating revenues	3,596	2,622
Depreciation and amortization	928	485
Income from operations	(412)	(575)
Income (Loss) from Continuing Operations, Net of Tax, Attributable to Parent	(594)	(903)
Capital expenditures	1,604	1,212
Total assets	139,057	160,835	157,043
Northwest Natural Gas Company [Member]
Segment Reporting Information [Line Items]
Operating revenues	312,350	282,529
Depreciation and amortization	27,169	24,190
Income from operations	95,118	77,021
Total assets	3,619,568	3,825,396	3,599,336
Northwest Natural Gas Company [Member] | Natural Gas Distribution [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Operating revenues	301,338	278,487
Northwest Natural Gas Company [Member] | Other Northwest Natural [Member] | Corporate, Non-Segment [Member]
Segment Reporting Information [Line Items]
Operating revenues	11,012	4,042
Northwest Natural Gas Company [Member] | Northwest Natural Gas Company [Member]
Segment Reporting Information [Line Items]
Operating revenues	312,350	282,529
Parent Company [Member]
Segment Reporting Information [Line Items]
Operating revenues	315,946	285,151
Depreciation and amortization	28,097	24,675
Income from operations	94,706	76,446
Income (Loss) from Continuing Operations, Net of Tax, Attributable to Parent	59,517	48,276
Capital expenditures	65,702	57,446
Total assets	$ 3,758,625	$ 3,986,231	$ 3,756,379