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Equity - Narrative - USD ($)
$ / shares in Units, $ in Thousands
3 Months Ended
Apr. 01, 2022
Mar. 31, 2023
Mar. 31, 2022
Dec. 31, 2022
Class of Stock [Line Items]        
Par Value (in dollars per share)   $ 0 $ 0 $ 0
Shares issued (in shares)   35,929,000 31,380,000 35,525,000
Stock Issued During Period, Shares, New Issues 2,875,000      
Proceeds from common stock issued, net $ 138,600 $ 16,669 $ 9,938  
Avion Water | Other Northwest Holdings [Member]        
Class of Stock [Line Items]        
Investment balance in Avion       $ 14,500
ATM Equity Program        
Class of Stock [Line Items]        
Par Value (in dollars per share)   $ 0    
Sale of Stock, Consideration Received on Transaction   $ 16,700    
Sale of Stock, Commissions and Fees Paid   $ 200    
Stock Issued During Period, Shares, New Issues   360,264    
nwn:AttheMarketEquityProgramEquityAvailableforIssuance   $ 94,100    
Maximum [Member] | Scenario, Plan | ATM Equity Program        
Class of Stock [Line Items]        
Cumulative Proceeds Received on All Transactions   $ 200,000