Property, Plant and Equipment - USD ($)	Jun. 30, 2021	Dec. 31, 2020	Jun. 30, 2020
Property, Plant and Equipment [Line Items]
Property, plant, and equipment	$ 3,849,792,000	$ 3,734,039,000	$ 3,608,902,000
Accumulated Depreciation, Depletion and Amortization, Property, Plant, and Equipment	1,093,863,000	1,079,269,000	1,062,299,000
Property, Plant and Equipment, Net	2,755,929,000	2,654,770,000	2,546,603,000
Natural Gas Distribution [Member]
Property, Plant and Equipment [Line Items]
Property, plant, and equipment	3,623,092,000	3,548,543,000	3,404,145,000
Public Utilities, Property, Plant and Equipment, Construction Work in Progress	99,646,000	63,901,000	90,903,000
Accumulated Depreciation, Depletion and Amortization, Property, Plant, and Equipment	1,068,603,000	1,055,809,000	1,040,616,000
Property, Plant and Equipment, Net	2,654,135,000	2,556,635,000	2,454,432,000
Other Northwest Natural [Member]
Property, Plant and Equipment [Line Items]
Property, plant, and equipment	66,315,000	66,300,000	64,317,000
Public Utilities, Property, Plant and Equipment, Construction Work in Progress	5,817,000	5,032,000	5,342,000
Accumulated Depreciation, Depletion and Amortization, Property, Plant, and Equipment	20,140,000	19,637,000	19,144,000
Property, Plant and Equipment, Net	51,992,000	51,695,000	50,515,000
Northwest Natural Gas Company [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Net	2,706,127,000	2,608,330,000	2,504,947,000
Property, Plant, Equipment non-cash	37,968,000	25,129,000	31,847,000
Other Northwest Holdings [Member]
Property, Plant and Equipment [Line Items]
Property, plant, and equipment	54,922,000	50,263,000	44,195,000
Accumulated Depreciation, Depletion and Amortization, Property, Plant, and Equipment	5,120,000	3,823,000	2,539,000
Property, Plant and Equipment, Net	49,802,000	46,440,000	41,656,000
Northwest Holdings [Member]
Property, Plant and Equipment [Line Items]
Property, Plant, Equipment non-cash	38,395	25,129	31,847
Northwest Natural Gas Company [Member]
Property, Plant and Equipment [Line Items]
Property, plant, and equipment	3,794,870,000	3,683,776,000	3,564,707,000
Accumulated Depreciation, Depletion and Amortization, Property, Plant, and Equipment	1,088,743,000	1,075,446,000	1,059,760,000
Property, Plant and Equipment, Net	$ 2,706,127,000	$ 2,608,330,000	$ 2,504,947,000