v3.26.1
Significant Accounting Policies - Schedule of Regulatory Asset Disclosure (Details) - USD ($)
$ in Thousands
Jun. 30, 2026
Dec. 31, 2025
Jun. 30, 2025
Regulatory Assets [Line Items]      
Regulatory assets, current $ 168,092 $ 143,745 $ 103,914
Regulatory assets, noncurrent 640,656 424,194 372,668
SiEnergy      
Regulatory Assets [Line Items]      
Regulatory assets, current 331 410 699
Regulatory assets, noncurrent 4,675 2,095 0
SiEnergy other      
Regulatory Assets [Line Items]      
Regulatory assets, noncurrent 1,636 1,412 995
NWN Water      
Regulatory Assets [Line Items]      
Regulatory assets, current 319 200 25
Regulatory assets, noncurrent 1,157 840 1,137
NW Natural      
Regulatory Assets [Line Items]      
Regulatory assets, current 167,442 143,135 103,190
Regulatory assets, noncurrent 633,188 419,847 370,536
NW Natural | Unrealized loss on derivatives      
Regulatory Assets [Line Items]      
Regulatory assets, current 36,508 63,578 25,977
Regulatory assets, noncurrent 17,541 14,039 7,908
NW Natural | Gas costs      
Regulatory Assets [Line Items]      
Regulatory assets, current 19,240 6,284 5,973
Regulatory assets, noncurrent 4,983 9,434 1,360
NW Natural | Environmental costs      
Regulatory Assets [Line Items]      
Regulatory assets, current 12,690 12,148 11,447
Regulatory assets, noncurrent 386,293 180,063 160,120
NW Natural | Decoupling      
Regulatory Assets [Line Items]      
Regulatory assets, current 42,164 11,631 9,313
Regulatory assets, noncurrent 11,069 8,891 1,534
NW Natural | Pension balancing      
Regulatory Assets [Line Items]      
Regulatory assets, current 7,131 7,131 7,131
Regulatory assets, noncurrent 12,004 15,647 18,169
NW Natural | Income taxes      
Regulatory Assets [Line Items]      
Regulatory assets, current 2,208 2,208 2,208
Regulatory assets, noncurrent 9,289 9,148 8,993
NW Natural | Pension and other postretirement benefit liabilities      
Regulatory Assets [Line Items]      
Regulatory assets, noncurrent 91,539 96,008 106,705
NW Natural | Washington Climate Commitment Act compliance      
Regulatory Assets [Line Items]      
Regulatory assets, current 7,754 7,482 7,874
Regulatory assets, noncurrent 48,228 33,085 32,851
NW Natural | Security and systems improvements      
Regulatory Assets [Line Items]      
Regulatory assets, current 1,270 1,771 2,018
Regulatory assets, noncurrent 8,085 8,234 8,369
NW Natural | Industrial demand side management      
Regulatory Assets [Line Items]      
Regulatory assets, current 12,181 10,539 13,612
Regulatory assets, noncurrent 2,604 9,334 1,906
NW Natural | Weather Adjusted Rate Mechanism      
Regulatory Assets [Line Items]      
Regulatory assets, current 15,099 9,932 8,708
Regulatory assets, noncurrent 3,424 6,062 1,332
NW Natural | Other      
Regulatory Assets [Line Items]      
Regulatory assets, current 11,197 10,431 8,929
Regulatory assets, noncurrent $ 38,129 $ 29,902 $ 21,289