Equity - Narrative - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended	9 Months Ended
	Sep. 30, 2023	Sep. 30, 2023	Sep. 30, 2022	Oct. 02, 2023	Dec. 31, 2022
Class of Stock [Line Items]
Par Value (in dollars per share)	$ 0	$ 0	$ 0		$ 0
Shares issued (in shares)	36,575,797	36,575,797	35,098,437		35,524,590
Proceeds from common stock issued, net		$ 40,955	$ 190,929
Subsequent Event [Member]
Class of Stock [Line Items]
Shares, Issued				184,832
Shares, Issued				184,832
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	$ 0
Sale of Stock, Consideration Received on Transaction	$ 18,800	$ 40,900
Sale of Stock, Commissions and Fees Paid	$ 300	$ 700
Stock Issued During Period, Shares, New Issues	475,732	955,325
nwn:AttheMarketEquityProgramEquityAvailableforIssuance	$ 69,500	$ 69,500
Maximum [Member] | Scenario, Plan | ATM Equity Program
Class of Stock [Line Items]
Cumulative Proceeds Received on All Transactions		$ 200,000