Equity - Narrative - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023	Dec. 31, 2023	Dec. 31, 2021
Class of Stock [Line Items]
Par Value (in dollars per share)	$ 0	$ 0	$ 0
Shares issued (in shares)	38,027,266	35,929,228	37,631,212
Proceeds from common stock issued, net	$ 12,218	$ 16,669
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	$ 12,200
Sale of Stock, Commissions and Fees Paid	$ 200
Stock Issued During Period, Shares, New Issues	333,000
nwn:AttheMarketEquityProgramEquityAvailableforIssuance	$ 31,000
Maximum [Member] | Scenario, Plan | ATM Equity Program
Class of Stock [Line Items]
Cumulative Proceeds Received on All Transactions	$ 200,000