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- Narrative (Details) - USD ($)
$ in Thousands
3 Months Ended 12 Months Ended
Dec. 31, 2018
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Property, Plant and Accrued Asset Removal Costs [Abstract]        
Weighted Average Depreciation Rates Transmission Distribution   2.70%    
Weighted Average Depreciation Rates Gas Storage   2.10%    
Weighted Average Depreciation Rates General Plant   4.50%    
Weighted Average Depreciation Rates Intangible Other   3.10%    
Public Utilities, AFUDC, Rate   5.20% 5.50% 0.70%
Revenue Recognition [Abstract]        
Accrued unbilled revenue $ 57,827 $ 57,827 $ 62,381  
Inventory Disclosure [Abstract]        
Inventory, Raw Materials and Supplies, Net of Reserves 14,200 14,200 10,900  
Goodwill and Intangible Assets Disclosure [Abstract]        
Goodwill 8,954 8,954 0  
Goodwill and Intangible Asset Impairment 0      
Operating Expenses   573,981 604,136 $ 517,456
Accounts Payable [Member]        
Cash and Cash Equivalents [Abstract]        
Bank Overdrafts 2,700 2,700 4,800  
Gill Ranch [Member] | Discontinued Operations, Held-for-sale [Member]        
Property, Plant and Accrued Asset Removal Costs [Abstract]        
Impairment of Long-Lived Assets   $ 0 $ 192,478 $ 0
Natural Gas Distribution [Member]        
Property, Plant and Accrued Asset Removal Costs [Abstract]        
Weighted-average depreciation rate, assets in service   2.80% 2.80% 2.80%
Northwest Natural Gas Company [Member]        
Industry Regulation [Abstract]        
Regulatory Asset, Amortization Period   12 months    
Regulatory Asset, Amortization Period, Low End of Range   less than one year    
Regulatory Liability, Amortization Period   12 months    
Regulatory Liability, Amortization Period, Low End Of Range   less than one year    
Revenue Recognition [Abstract]        
Accrued unbilled revenue 57,773 $ 57,773 $ 62,381  
Revenue Taxes [Abstract]        
Revenue Taxes   30,100 19,100 $ 17,100
Inventory Disclosure [Abstract]        
Inventory - Gas $ 29,900 29,900 36,700  
Goodwill and Intangible Assets Disclosure [Abstract]        
Operating Expenses   $ 572,472 $ 604,116 $ 516,662
Northwest Natural Gas Company [Member] | Oregon [Member]        
Derivative Instruments and Hedging Activities Disclosure [Abstract]        
PGA deferral rate   90.00% 90.00% 90.00%
Northwest Natural Gas Company [Member] | Oregon [Member] | Minimum [Member]        
Derivative Instruments and Hedging Activities Disclosure [Abstract]        
PGA deferral rate   80.00%    
Impact on earnings from gas cost sharing   10.00%    
Northwest Natural Gas Company [Member] | Oregon [Member] | Maximum [Member]        
Derivative Instruments and Hedging Activities Disclosure [Abstract]        
PGA deferral rate   90.00%    
Impact on earnings from gas cost sharing   20.00%    
Northwest Natural Gas Company [Member] | Washington [Member]        
Derivative Instruments and Hedging Activities Disclosure [Abstract]        
PGA deferral rate   100.00% 100.00% 100.00%
Asset Recoverable Gas Costs [Member] | Northwest Natural Gas Company [Member]        
Industry Regulation [Abstract]        
Regulatory Liability, Amortization Period   12 months