Property, Plant and Equipment - USD ($)	Mar. 31, 2021	Dec. 31, 2020	Mar. 31, 2020
Property, Plant and Equipment [Line Items]
Property, plant, and equipment	$ 3,788,283,000	$ 3,734,039,000	$ 3,551,065,000
Accumulated Depreciation, Depletion and Amortization, Property, Plant, and Equipment	1,091,903,000	1,079,269,000	1,050,850,000
Property, Plant and Equipment, Net	2,696,380,000	2,654,770,000	2,500,215,000
Natural Gas Distribution [Member]
Property, Plant and Equipment [Line Items]
Property, plant, and equipment	3,594,226,000	3,548,543,000	3,344,345,000
Public Utilities, Property, Plant and Equipment, Construction Work in Progress	70,766,000	63,901,000	95,566,000
Accumulated Depreciation, Depletion and Amortization, Property, Plant, and Equipment	1,067,502,000	1,055,809,000	1,030,234,000
Property, Plant and Equipment, Net	2,597,490,000	2,556,635,000	2,409,677,000
Other Northwest Natural [Member]
Property, Plant and Equipment [Line Items]
Property, plant, and equipment	66,314,000	66,300,000	64,314,000
Public Utilities, Property, Plant and Equipment, Construction Work in Progress	5,125,000	5,032,000	4,824,000
Accumulated Depreciation, Depletion and Amortization, Property, Plant, and Equipment	19,889,000	19,637,000	18,901,000
Property, Plant and Equipment, Net	51,550,000	51,695,000	50,237,000
Northwest Natural Gas Company [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Net	2,649,040,000	2,608,330,000	2,459,914,000
Property, Plant, Equipment non-cash	20,969,000	25,129,000	33,999,000
Other Northwest Holdings [Member]
Property, Plant and Equipment [Line Items]
Property, plant, and equipment	51,852,000	50,263,000	42,016,000
Accumulated Depreciation, Depletion and Amortization, Property, Plant, and Equipment	4,512,000	3,823,000	1,715,000
Property, Plant and Equipment, Net	47,340,000	46,440,000	40,301,000
Northwest Holdings [Member]
Property, Plant and Equipment [Line Items]
Property, Plant, Equipment non-cash	21,118	25,129	33,999
Northwest Natural Gas Company [Member]
Property, Plant and Equipment [Line Items]
Property, plant, and equipment	3,736,431,000	3,683,776,000	3,509,049,000
Accumulated Depreciation, Depletion and Amortization, Property, Plant, and Equipment	1,087,391,000	1,075,446,000	1,049,135,000
Property, Plant and Equipment, Net	$ 2,649,040,000	$ 2,608,330,000	$ 2,459,914,000

Property, Plant, Equipment non-cash

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- Definition

Amount of accumulated depreciation, depletion and amortization for physical assets used in the normal conduct of business to produce goods and services.

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Amount before accumulated depreciation, depletion and amortization of physical assets used in the normal conduct of business and not intended for resale. Examples include, but are not limited to, land, buildings, machinery and equipment, office equipment, and furniture and fixtures.

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- Definition

Period end amount of construction work in progress in public utility.

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