v3.26.1
Pension and Other Postretirement Benefit Costs - Schedule of Amounts Recognized in Other Comprehensive Income (Loss) (Details) - USD ($)
$ in Thousands
 3 Months Ended 6 Months Ended
Jun. 30, 2026
Jun. 30, 2025
Jun. 30, 2026
Jun. 30, 2025
Accumulated Other Comprehensive Income Loss Net Of Tax [Roll Forward]        
Beginning balance     $ 1,475,076  
Ending balance $ 1,559,295 $ 1,459,238 1,559,295 $ 1,459,238
NW Natural        
Accumulated Other Comprehensive Income Loss Net Of Tax [Roll Forward]        
Beginning balance     1,508,244  
Ending balance 1,566,080 1,517,202 1,566,080 1,517,202
Non-Qualified Pension Plans, Defined Benefit | NW Natural        
Accumulated Other Comprehensive Income Loss Net Of Tax [Roll Forward]        
Beginning balance (4,614) (6,877) (4,705) (7,052)
Total reclassifications before tax 124 199 248 399
Tax benefit (33) (25) (66) (50)
Total reclassifications for the period 91 174 182 349
Ending balance (4,523) (6,703) (4,523) (6,703)
Non-Qualified Pension Plans, Defined Benefit | NW Natural | Accumulated Defined Benefit Plans Adjustment, Net Gain (Loss) Attributable to Parent        
Accumulated Other Comprehensive Income Loss Net Of Tax [Roll Forward]        
Total reclassifications before tax $ 124 $ 199 $ 248 $ 399