Derivative Instruments - Schedule of Income Statement Presentation of Derivative Instruments (Details) - Northwest Holdings and Northwest Natural - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2026	Jun. 30, 2025	Jun. 30, 2026	Jun. 30, 2025
Natural gas commodity
Derivative [Line Items]
Total gain (loss) in pre-tax earnings	$ 0	$ 0	$ 0	$ 0
Natural gas commodity \| Amounts deferred to regulatory accounts on balance sheet
Derivative [Line Items]
Total gain (loss) in pre-tax earnings	(8,416)	(4,651)	6,613	(34,348)
Natural gas commodity \| Location, Statement of Income, Balance [Axis]: us-gaap:UtilitiesOperatingExpenseGasAndPetroleumPurchased
Derivative [Line Items]
Total gain (loss) in pre-tax earnings	8,416	4,651	(6,613)	34,348
Foreign Exchange
Derivative [Line Items]
Total gain (loss) in pre-tax earnings	0	0	0	0
Foreign Exchange \| Amounts deferred to regulatory accounts on balance sheet
Derivative [Line Items]
Total gain (loss) in pre-tax earnings	170	(302)	284	(278)
Foreign Exchange \| Location, Statement of Income, Balance [Axis]: us-gaap:UtilitiesOperatingExpenseGasAndPetroleumPurchased
Derivative [Line Items]
Total gain (loss) in pre-tax earnings	$ (170)	$ 302	$ (284)	$ 278