Pension and Other Postretirement Benefits Costs - Schedule of AOCL and Changes in AOCL, Non-Qualified Employee Plans (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	$ 6,285
Ending balance	7,049	$ 6,285
Northwest Holdings and Northwest Natural [Member] | Non-Qualified Pension Plans, Defined Benefit [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	6,414	11,404
Amounts reclassified to AOCL	(1,676)	5,706
Amortization of actuarial losses	558	1,081
Total reclassifications before tax	(1,118)	6,787
Tax benefit (expense)	295	(1,797)
Total reclassifications for the period	(823)	4,990
Ending balance	(7,237)	6,414
Northwest Natural Gas Company [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	6,414
Ending balance	$ 7,237	$ 6,414