Equity - Narrative - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended	6 Months Ended
	Jun. 30, 2023	Jun. 30, 2023	Jun. 30, 2022	Dec. 31, 2022
Class of Stock [Line Items]
Par Value (in dollars per share)	$ 0	$ 0	$ 0	$ 0
Shares issued (in shares)	36,065,000	36,065,000	34,754,000	35,525,000
Proceeds from common stock issued, net		$ 22,072	$ 174,053
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	$ 5,400
Sale of Stock, Commissions and Fees Paid	$ 200
Stock Issued During Period, Shares, New Issues	119,329
nwn:AttheMarketEquityProgramEquityAvailableforIssuance	$ 88,600	$ 88,600
Maximum [Member] | Scenario, Plan | ATM Equity Program
Class of Stock [Line Items]
Cumulative Proceeds Received on All Transactions		$ 200,000