Property, Plant and Equipment (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Property, Plant and Equipment, Net, by Type [Abstract]
Property, Plant and Equipment, Gross	$ 3,414,490	$ 3,204,635
Accumulated Depreciation, Depletion and Amortization, Property, Plant, and Equipment	993,118	960,477
Total property, plant, and equipment, net	2,421,372	2,244,158
Regulatory Liability, Noncurrent	611,560	586,093
Acquired Equipment Capital Leases	0	0
Natural Gas Distribution [Member]
Property, Plant and Equipment, Net, by Type [Abstract]
Property, Plant and Equipment, Gross	3,134,122	2,975,217
Public Utilities, Property, Plant and Equipment, Construction Work in Progress	204,978	159,924
Accumulated Depreciation, Depletion and Amortization, Property, Plant, and Equipment	974,252	942,879
Total property, plant, and equipment, net	2,364,848	2,192,262
Northwest Holdings and Northwest Natural [Member]
Property, Plant and Equipment, Net, by Type [Abstract]
Property, Plant, Equipment non-cash	23,676	34,761
Other Northwest Natural [Member]
Property, Plant and Equipment, Net, by Type [Abstract]
Property, Plant and Equipment, Gross	66,009	64,997
Public Utilities, Property, Plant and Equipment, Construction Work in Progress	5,330	4,122
Accumulated Depreciation, Depletion and Amortization, Property, Plant, and Equipment	18,603	17,406
Total property, plant, and equipment, net	52,736	51,713
Northwest Natural Gas Company [Member]
Property, Plant and Equipment, Net, by Type [Abstract]
Total property, plant, and equipment, net	2,417,584	2,243,975
Northwest Holdings Other [Member]
Property, Plant and Equipment, Net, by Type [Abstract]
Property, Plant and Equipment, Gross	4,051	375
Accumulated Depreciation, Depletion and Amortization, Property, Plant, and Equipment	263	192
Total property, plant, and equipment, net	$ 3,788	$ 183
Natural Gas Distribution [Member]
Property, Plant and Equipment, Net, by Type [Abstract]
Public Utilities, Property, Plant and Equipment, Disclosure of Composite Depreciation Rate for Plants in Service	2.80%	2.80%	2.80%
Other Northwest Natural [Member]
Property, Plant and Equipment, Net, by Type [Abstract]
Weighted Average Depreciation Rates	2.20%	1.90%	2.00%
Northwest Natural Gas Company [Member]
Property, Plant and Equipment, Net, by Type [Abstract]
Property, Plant and Equipment, Gross	$ 3,410,439	$ 3,204,260
Accumulated Depreciation, Depletion and Amortization, Property, Plant, and Equipment	992,855	960,285
Total property, plant, and equipment, net	2,417,584	2,243,975
Regulatory Liability, Noncurrent	611,560	586,093
Northwest Natural Gas Company [Member] | Asset Removal Costs [Member]
Property, Plant and Equipment, Net, by Type [Abstract]
Regulatory Liability, Noncurrent	$ 380,500	$ 360,929