Segment Information - Schedule of Summarized Financial Information by Segment (Details) - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019
Segment Reporting Information [Line Items]
Operating revenues	$ 285,151	$ 285,348
Depreciation and amortization	24,675	21,572
Income from operations	76,446	76,045
Income (Loss) from Continuing Operations, Net of Tax, Attributable to Parent	48,276	43,418
Total assets	4,001,527	3,191,117	$ 3,428,454
Discontinued operations - total assets	15,300	14,600	15,100
Natural Gas Distribution [Member] \| Operating Segments [Member]
Segment Reporting Information [Line Items]
Operating revenues	278,487	279,041
Depreciation and amortization	23,946	21,249
Income from operations	75,258	72,898
Income (Loss) from Continuing Operations, Net of Tax, Attributable to Parent	47,943	41,206
Capital expenditures	56,157	48,606
Total assets	3,776,650	3,091,062	3,273,835
Other Northwest Natural [Member] \| Corporate, Non-Segment [Member]
Segment Reporting Information [Line Items]
Operating revenues	4,042	5,805
Depreciation and amortization	244	255
Income from operations	1,763	3,746
Income (Loss) from Continuing Operations, Net of Tax, Attributable to Parent	1,236	2,689
Capital expenditures	77	52
Total assets	48,746	49,566	47,652
Northwest Natural Gas Company [Member] \| Operating Segments [Member]
Segment Reporting Information [Line Items]
Operating revenues	282,529	284,846
Depreciation and amortization	24,190	21,504
Income from operations	77,021	76,644
Income (Loss) from Continuing Operations, Net of Tax, Attributable to Parent	49,179	43,895
Capital expenditures	56,234	48,658
Total assets	3,825,396	3,140,628	3,321,487
Other Northwest Holdings [Member] \| Corporate, Non-Segment [Member]
Segment Reporting Information [Line Items]
Operating revenues	2,622	502
Depreciation and amortization	485	68
Income from operations	(575)	(599)
Income (Loss) from Continuing Operations, Net of Tax, Attributable to Parent	(903)	(477)
Capital expenditures	1,212	106
Total assets	160,835	35,857	91,833
Northwest Natural Gas Company [Member]
Segment Reporting Information [Line Items]
Operating revenues	282,529	284,846
Depreciation and amortization	24,190	21,504
Income from operations	77,021	76,644
Total assets	3,825,396	3,140,628	3,321,487
Northwest Natural Gas Company [Member] \| Natural Gas Distribution [Member] \| Operating Segments [Member]
Segment Reporting Information [Line Items]
Operating revenues	278,487	279,041
Northwest Natural Gas Company [Member] \| Other Northwest Natural [Member] \| Corporate, Non-Segment [Member]
Segment Reporting Information [Line Items]
Operating revenues	4,042	5,805
Northwest Natural Gas Company [Member] \| Northwest Natural Gas Company [Member]
Segment Reporting Information [Line Items]
Operating revenues	282,529	284,846
Parent Company [Member]
Segment Reporting Information [Line Items]
Operating revenues	285,151	285,348
Depreciation and amortization	24,675	21,572
Income from operations	76,446	76,045
Income (Loss) from Continuing Operations, Net of Tax, Attributable to Parent	48,276	43,418
Capital expenditures	57,446	48,764
Total assets	$ 3,986,231	$ 3,176,485	$ 3,413,320

Sum of the carrying amounts as of the balance sheet date of all assets that are recognized. Assets are probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.

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