Property, Plant and Equipment (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2019	Dec. 31, 2018	Sep. 30, 2018
Property, Plant and Equipment [Line Items]
Property, plant, and equipment	$ 3,416,718	$ 3,414,490	$ 3,370,388
Accumulated Depreciation, Depletion and Amortization, Property, Plant, and Equipment	1,027,330	993,118	996,994
Property, Plant and Equipment, Net	2,389,388	2,421,372	2,373,394
Other Liabilities, Noncurrent	123,352	147,763	140,475
Natural Gas Distribution [Member]
Property, Plant and Equipment [Line Items]
Property, plant, and equipment	3,236,227	3,134,122	3,068,235
Public Utilities, Property, Plant and Equipment, Construction Work in Progress	91,302	204,978	227,200
Accumulated Depreciation, Depletion and Amortization, Property, Plant, and Equipment	1,007,742	974,252	978,446
Property, Plant and Equipment, Net	2,319,787	2,364,848	2,316,989
Other Northwest Natural [Member]
Property, Plant and Equipment [Line Items]
Property, plant, and equipment	63,360	66,009	65,957
Public Utilities, Property, Plant and Equipment, Construction Work in Progress	6,164	5,330	5,505
Accumulated Depreciation, Depletion and Amortization, Property, Plant, and Equipment	18,889	18,603	18,335
Property, Plant and Equipment, Net	50,635	52,736	53,127
Northwest Natural Gas Company [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Net	2,370,422	2,417,584	2,370,116
Other Northwest Holdings [Member]
Property, Plant and Equipment [Line Items]
Property, plant, and equipment	19,665	4,051	3,491
Accumulated Depreciation, Depletion and Amortization, Property, Plant, and Equipment	699	263	213
Property, Plant and Equipment, Net	18,966	3,788	3,278
Northwest Holdings and Northwest Natural [Member]
Property, Plant and Equipment [Line Items]
Property, Plant, Equipment non-cash	$ 35,461	23,676	27,692
New Headquarters Lease [Member]
Property, Plant and Equipment [Line Items]
Lessee, Operating Lease, Lease Not yet Commenced, Term of Contract	20 years
New Headquarters Lease [Member] | Accounting Standards Update 2016-02 [Member] | Build to Suit Lease [Member]
Property, Plant and Equipment [Line Items]
Property, plant, and equipment		26,000
Other Liabilities, Noncurrent		26,000
Northwest Natural Gas Company [Member]
Property, Plant and Equipment [Line Items]
Property, plant, and equipment	$ 3,397,053	3,410,439	3,366,896
Accumulated Depreciation, Depletion and Amortization, Property, Plant, and Equipment	1,026,631	992,855	996,780
Property, Plant and Equipment, Net	2,370,422	2,417,584	2,370,116
Other Liabilities, Noncurrent	123,259	$ 147,668	$ 140,390
Northwest Natural Gas Company [Member] | North Mist Lease [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Transfers and Changes	$ 146,000