Pension and Other Postretirement Benefit Costs - Narrative - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022	Jun. 30, 2023	Dec. 31, 2022	Jun. 30, 2022	Dec. 31, 2021
Pension and Other Postretirement Benefits Cost (Reversal of Cost) [Abstract]
Defined benefit pension plan cash contributions			$ 0
Estimated future employer contributions in next fiscal year	$ 0		0
Employer contributions			8,000	$ 7,400
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Accumulated other comprehensive loss	(4,979)	$ (10,808)	(4,979)	(10,808)		$ (6,285)
Northwest Natural Gas Company [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Accumulated other comprehensive loss	(6,107)	(10,808)	(6,107)	(10,808)		(6,414)
Non-Qualified Pension Plans, Defined Benefit | Northwest Natural Gas Company [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Accumulated other comprehensive loss	(6,107)	(10,808)	(6,107)	(10,808)	$ (6,209)	$ (6,414)	$ (11,010)	$ (11,404)
Amortization of actuarial losses	139	275	418	811
Other Comprehensive (Income) Loss, Defined Benefit Plan, after Reclassification Adjustment, before Tax	139	275	418	811
Tax benefit	(37)	(73)	(111)	(215)
Other Comprehensive (Income) Loss, Defined Benefit Plan, after Reclassification Adjustment, after Tax	$ 102	$ 202	$ 307	$ 596