Pension and Other Postretirement Benefit Costs - Amounts Recognized in Accumulated Other Comprehensive Loss - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022
Defined Benefit Plan, Amounts Recognized in Other Comprehensive Income (Loss) [Abstract]
Beginning balance			$ (6,285)
Ending balance	$ (5,255)	$ (11,010)	(5,255)	$ (11,010)
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Accumulated other comprehensive loss	(5,255)	(11,010)	(5,255)	(11,010)
Northwest Natural Gas Company [Member]
Defined Benefit Plan, Amounts Recognized in Other Comprehensive Income (Loss) [Abstract]
Beginning balance			(6,414)
Ending balance	(6,209)	(11,010)	(6,209)	(11,010)
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Accumulated other comprehensive loss	(6,209)	(11,010)	(6,209)	(11,010)
Non-Qualified Pension Plans, Defined Benefit | Northwest Natural Gas Company [Member]
Defined Benefit Plan, Amounts Recognized in Other Comprehensive Income (Loss) [Abstract]
Beginning balance	(6,312)	(11,207)	(6,414)	(11,404)
Amortization of actuarial losses	140	268	279	536
Total reclassifications before tax	140	268	279	536
Tax benefit	(37)	(71)	(74)	(142)
Total reclassifications for the period	103	197	205	394
Ending balance	(6,209)	(11,010)	(6,209)	(11,010)
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Accumulated other comprehensive loss	(6,209)	(11,010)	(6,209)	(11,010)
Amortization of actuarial losses	140	268	279	536
Other Comprehensive (Income) Loss, Defined Benefit Plan, after Reclassification Adjustment, before Tax	140	268	279	536
Other Comprehensive (Income) Loss, Defined Benefit Plan, after Reclassification Adjustment, Tax, Attributable to Parent	37	71	74	142
Other Comprehensive (Income) Loss, Defined Benefit Plan, after Reclassification Adjustment, after Tax	$ 103	$ 197	$ 205	$ 394