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Long-Term Debt - USD ($)
$ in Thousands
6 Months Ended 12 Months Ended
Jun. 30, 2023
Jun. 30, 2022
Dec. 31, 2022
Aug. 04, 2023
Debt Instrument [Line Items]        
Long-term Debt $ 1,535,292 $ 1,045,881 $ 1,336,864  
Other Long-Term Debt 5,900 4,200 6,200  
Unamortized debt issuance costs 10,261 8,031 8,987  
Long-term Debt, Gross 1,545,553 1,053,912 1,345,851  
Long-term debt, Current Maturities, Gross 240,700 400 90,700  
Long-term debt 1,294,578 1,045,530 1,246,167  
Northwest Natural Gas Company [Member]        
Debt Instrument [Line Items]        
Long-term Debt 1,324,559 986,762 1,125,877  
Unamortized debt issuance costs $ 10,141 $ 7,938 $ 8,823  
Weighted average interest rate 4.70% 4.40% 4.50%  
Long-term Debt, Gross $ 1,334,700 $ 994,700 $ 1,134,700  
Long-term debt $ 1,234,577 $ 986,762 $ 1,035,935  
Northwest Natural Gas Company [Member] | Minimum [Member]        
Debt Instrument [Line Items]        
Stated interest rate 2.80%      
Northwest Natural Gas Company [Member] | Maximum [Member]        
Debt Instrument [Line Items]        
Stated interest rate 7.90%      
18 Month Credit Agreement Due March 15, 2024        
Debt Instrument [Line Items]        
Weighted average interest rate 5.50% 0.00% 4.20%  
Long-term Debt, Term 18 months      
Proceeds from Issuance of Debt $ 100,000 $ 0 $ 100,000  
Debt Instrument Covenant Consolidated Indebtedness to Capitalization Ratio 70.00%      
Derivative, Fixed Interest Rate 4.70%      
18 Month Credit Agreement Due March 15, 2024 | NWN Water        
Debt Instrument [Line Items]        
Weighted average interest rate 5.50% 0.00% 4.20%  
Long-term Debt, Term 18 months      
Proceeds from Issuance of Debt $ 50,000 $ 0 $ 50,000  
Debt Instrument Covenant Consolidated Indebtedness to Capitalization Ratio 70.00%      
First Mortgage Bonds 4.8 Percent Series Due 2052 | Northwest Natural Gas Company [Member]        
Debt Instrument [Line Items]        
Stated interest rate 4.80%      
Proceeds from Issuance of Debt $ 140,000      
NWN Water Term Loan Due 2026        
Debt Instrument [Line Items]        
Derivative, Fixed Interest Rate 3.80%      
NWN Water Term Loan Due 2026 | Corporate, Non-Segment [Member] | Other Northwest Holdings [Member]        
Debt Instrument [Line Items]        
Long-term Debt $ 55,000      
NWN Water Term Loan Due 2026 | NWN Water        
Debt Instrument [Line Items]        
Long-term Debt $ 55,000 $ 55,000 $ 55,000  
Weighted average interest rate 4.80% 2.30% 2.50%  
Note 5430 Series Due 2053        
Debt Instrument [Line Items]        
Stated interest rate 5.43%      
Note 5430 Series Due 2053 | Northwest Natural Gas Company [Member]        
Debt Instrument [Line Items]        
Stated interest rate 5.43%      
Proceeds from Issuance of First Mortgage Bond $ 100,000      
Secured Debt $ 100,000      
Note 5750 | Northwest Natural Gas Company [Member]        
Debt Instrument [Line Items]        
Stated interest rate 5.75%      
Proceeds from Issuance of Medium-term Notes $ 100,000      
Note 5180 due 2034 | Forecast [Member]        
Debt Instrument [Line Items]        
Stated interest rate       5.18%
Note 5180 due 2034 | Northwest Natural Gas Company [Member] | Forecast [Member]        
Debt Instrument [Line Items]        
Secured Debt       $ 80,000
Note 5230 due 2038 | Forecast [Member]        
Debt Instrument [Line Items]        
Stated interest rate       5.23%
Note 5230 due 2038 | Northwest Natural Gas Company [Member] | Forecast [Member]        
Debt Instrument [Line Items]        
Secured Debt       $ 50,000