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Segment Information - Narrative (Details)
$ in Thousands
12 Months Ended
Dec. 31, 2021
USD ($)
Dec. 31, 2020
USD ($)
Dec. 31, 2019
USD ($)
Segment Reporting Information [Line Items]      
Assets $ 4,064,604 $ 3,756,379  
Operating Segments [Member]      
Segment Reporting Information [Line Items]      
Number of Reportable Segments 1    
Operating Segments [Member] | Natural Gas Distribution [Member]      
Segment Reporting Information [Line Items]      
Assets $ 3,846,112 $ 3,549,868 $ 3,273,835
Northwest Holdings and Northwest Natural [Member] | Natural Gas Distribution [Member]      
Segment Reporting Information [Line Items]      
Percent Of Pre Tax Income From Gas Storage Retained When The Costs Of The Capacity Are Not In Utility Rates 80.00%    
Percent Of Pre Tax Income From Gas Storage Retained When The Costs Of The Capacity Are In Utility Rates 10.00%    
Percent Of Pre Tax Income From Gas Storage Credited To Deferred Regulatory Account 20.00%    
Percent Of Pre Tax Income From Gas Storage Credited To Deferred Regulatory Account When In Rates 90.00%    
Northwest Holdings and Northwest Natural [Member] | Operating Segments [Member]      
Segment Reporting Information [Line Items]      
Segment Reporting, Disclosure of Major Customers No    
Customer Total [Member] | Geographic Concentration Risk [Member] | Oregon [Member] | Natural Gas Distribution [Member]      
Segment Reporting Information [Line Items]      
Concentration Risk, Percentage 88.00%    
Customer Total [Member] | Geographic Concentration Risk [Member] | WASHINGTON | Natural Gas Distribution [Member]      
Segment Reporting Information [Line Items]      
Concentration Risk, Percentage 12.00%    
Volumes Delivered [Member] | Volumes Delivered [Member] | Residential and Commerical Customers [Member] | Natural Gas Distribution [Member]      
Segment Reporting Information [Line Items]      
Concentration Risk, Percentage 60.00%    
Gross Profit Margin [Member] | Residential and Commerical Customers [Member] | Residential and Commerical Customers [Member] | Natural Gas Distribution [Member]      
Segment Reporting Information [Line Items]      
Concentration Risk, Percentage 90.00%