Property, Plant and Equipment - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019	Sep. 30, 2019
Property, Plant and Equipment [Line Items]
Property, plant, and equipment	$ 3,680,872	$ 3,476,746	$ 3,416,718
Accumulated Depreciation, Depletion and Amortization, Property, Plant, and Equipment	1,073,623	1,037,847	1,027,330
Property, Plant and Equipment, Net	2,607,249	2,438,899	2,389,388
Natural Gas Distribution [Member]
Property, Plant and Equipment [Line Items]
Property, plant, and equipment	3,441,301	3,302,049	3,236,227
Public Utilities, Property, Plant and Equipment, Construction Work in Progress	120,722	84,965	91,302
Accumulated Depreciation, Depletion and Amortization, Property, Plant, and Equipment	1,051,018	1,017,931	1,007,742
Property, Plant and Equipment, Net	2,511,005	2,369,083	2,319,787
Other Northwest Natural [Member]
Property, Plant and Equipment [Line Items]
Property, plant, and equipment	65,103	63,513	63,360
Public Utilities, Property, Plant and Equipment, Construction Work in Progress	6,444	5,548	6,164
Accumulated Depreciation, Depletion and Amortization, Property, Plant, and Equipment	19,387	18,662	18,889
Property, Plant and Equipment, Net	52,160	50,399	50,635
Northwest Natural Gas Company [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Net	2,563,165	2,419,482	2,370,422
Other Northwest Holdings [Member]
Property, Plant and Equipment [Line Items]
Property, plant, and equipment	47,302	20,671	19,665
Accumulated Depreciation, Depletion and Amortization, Property, Plant, and Equipment	3,218	1,254	699
Property, Plant and Equipment, Net	44,084	19,417	18,966
Northwest Holdings and Northwest Natural [Member]
Property, Plant and Equipment [Line Items]
Property, Plant, Equipment non-cash	37,236	32,502	35,461
Northwest Natural Gas Company [Member]
Property, Plant and Equipment [Line Items]
Property, plant, and equipment	3,633,570	3,456,075	3,397,053
Accumulated Depreciation, Depletion and Amortization, Property, Plant, and Equipment	1,070,405	1,036,593	1,026,631
Property, Plant and Equipment, Net	$ 2,563,165	$ 2,419,482	$ 2,370,422

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

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