Pension and Other Postretirement Benefit Costs - Amounts Recognized in Accumulated Other Comprehensive Loss - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Defined Benefit Plan, Amounts Recognized in Other Comprehensive Income (Loss) [Abstract]
Beginning balance	$ (7,049)
Ending balance	(6,825)	$ (6,594)
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Accumulated other comprehensive loss	(6,825)	(6,594)
Northwest Natural Gas Company [Member]
Defined Benefit Plan, Amounts Recognized in Other Comprehensive Income (Loss) [Abstract]
Beginning balance	(7,237)
Ending balance	(7,359)	(6,312)
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Accumulated other comprehensive loss	(7,359)	(6,312)
Non-Qualified Pension Plans, Defined Benefit | Northwest Natural Gas Company [Member]
Defined Benefit Plan, Amounts Recognized in Other Comprehensive Income (Loss) [Abstract]
Beginning balance	(7,237)	(6,414)
Amortization of actuarial losses	173	139
Total reclassifications before tax	(10)	139
Tax benefit	(112)	(37)
Total reclassifications for the period	(122)	102
Ending balance	(7,359)	(6,312)
Other Comprehensive Income (Loss), Defined Benefit Plan, Gain (Loss), Reclassification Adjustment to AOCI, before Tax	183	0
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Accumulated other comprehensive loss	(7,359)	(6,312)
Other Comprehensive Income (Loss), Defined Benefit Plan, Gain (Loss), Reclassification Adjustment to AOCI, before Tax	183	0
Amortization of actuarial losses	173	139
Other Comprehensive (Income) Loss, Defined Benefit Plan, after Reclassification Adjustment, before Tax	(10)	139
Other Comprehensive (Income) Loss, Defined Benefit Plan, after Reclassification Adjustment, Tax, Attributable to Parent	112	37
Other Comprehensive (Income) Loss, Defined Benefit Plan, after Reclassification Adjustment, after Tax	$ (122)	$ 102