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Equity - Narrative - USD ($)
$ / shares in Units, $ in Thousands
3 Months Ended 9 Months Ended
Apr. 01, 2022
Sep. 30, 2022
Sep. 30, 2022
Sep. 30, 2021
Dec. 31, 2021
Class of Stock [Line Items]          
Par Value (in dollars per share)   $ 0 $ 0 $ 0 $ 0
Shares issued (in shares)   35,098,000 35,098,000 30,730,000 31,129,000
Stock Issued During Period, Shares, New Issues 2,875,000        
Proceeds from common stock issued, net $ 138,600   $ 190,929 $ 2,107  
Avion Water | Other Northwest Holdings [Member]          
Class of Stock [Line Items]          
Investment balance in Avion         $ 14,500
Northwest Natural Gas Company [Member]          
Class of Stock [Line Items]          
Repayments of Short-term Debt $ 130,000        
ATM Equity Program          
Class of Stock [Line Items]          
Par Value (in dollars per share)   $ 0 $ 0    
Sale of Stock, Consideration Received on Transaction   $ 16,700 $ 51,900    
Sale of Stock, Commissions and Fees Paid   $ 300 $ 1,000    
Stock Issued During Period, Shares, New Issues   327,221 1,005,322    
nwn:AttheMarketEquityProgramEquityAvailableforIssuance   $ 129,200 $ 129,200    
Maximum [Member] | Scenario, Plan | ATM Equity Program          
Class of Stock [Line Items]          
Cumulative Proceeds Received on All Transactions     $ 200,000