Property, Plant and Equipment (Details) - USD ($) $ in Thousands	6 Months Ended
Jun. 30, 2019	Jun. 30, 2020	Dec. 31, 2019
Property, Plant and Equipment [Line Items]
Property, plant, and equipment	$ 3,355,811	$ 3,608,902	$ 3,476,746
Accumulated Depreciation, Depletion and Amortization, Property, Plant, and Equipment	1,016,185	1,062,299	1,037,847
Property, Plant and Equipment, Net	2,339,626	2,546,603	2,438,899
Natural Gas Distribution [Member]
Property, Plant and Equipment [Line Items]
Property, plant, and equipment	3,193,121	3,404,145	3,302,049
Public Utilities, Property, Plant and Equipment, Construction Work in Progress	75,045	90,903	84,965
Accumulated Depreciation, Depletion and Amortization, Property, Plant, and Equipment	997,111	1,040,616	1,017,931
Property, Plant and Equipment, Net	2,271,055	2,454,432	2,369,083
Other Northwest Natural [Member]
Property, Plant and Equipment [Line Items]
Property, plant, and equipment	63,385	64,317	63,513
Public Utilities, Property, Plant and Equipment, Construction Work in Progress	5,454	5,342	5,548
Accumulated Depreciation, Depletion and Amortization, Property, Plant, and Equipment	18,650	19,144	18,662
Property, Plant and Equipment, Net	50,189	50,515	50,399
Northwest Natural Gas Company [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Net	2,321,244	2,504,947	2,419,482
Other Northwest Holdings [Member]
Property, Plant and Equipment [Line Items]
Property, plant, and equipment	18,806	44,195	20,671
Accumulated Depreciation, Depletion and Amortization, Property, Plant, and Equipment	424	2,539	1,254
Property, Plant and Equipment, Net	18,382	41,656	19,417
Northwest Holdings and Northwest Natural [Member]
Property, Plant and Equipment [Line Items]
Property, Plant, Equipment non-cash	32,923	31,847	32,502
Northwest Natural Gas Company [Member]
Property, Plant and Equipment [Line Items]
Property, plant, and equipment	3,337,005	3,564,707	3,456,075
Accumulated Depreciation, Depletion and Amortization, Property, Plant, and Equipment	1,015,761	1,059,760	1,036,593
Property, Plant and Equipment, Net	2,321,244	$ 2,504,947	$ 2,419,482
Northwest Natural Gas Company [Member] \| North Mist Lease [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Transfers and Changes	$ 146,000

Property, Plant, Equipment non-cash

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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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Amount after accumulated depreciation, depletion and amortization of physical assets used in the normal conduct of business to produce goods and services 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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Amount of increase (decrease) of physical assets used in the normal conduct of business and not intended for resale, from reclassification, impairment, donation, or changes classified as other. 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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