v3.26.1
DEBT - Long-Term Debt (Details) - USD ($)
$ in Thousands
Jun. 30, 2026
Dec. 31, 2025
Jun. 30, 2025
Debt Instrument [Line Items]      
Balance Outstanding $ 2,518,500 $ 2,448,700 $ 2,242,300
Long-term debt 2,502,400    
Less: unamortized debt issuance costs 16,100 15,900 14,100
Current maturities of long-term debt 125,685 160,627 141,541
Long-term debt 2,376,685 2,272,202 2,086,650
NW Natural      
Debt Instrument [Line Items]      
Balance Outstanding 1,544,700 1,544,700 1,374,700
Long-term debt 1,535,300 1,534,900 1,365,700
Less: unamortized debt issuance costs 9,400 9,800 9,000
Current maturities of long-term debt 74,972 54,948 29,997
Long-term debt 1,460,280 1,479,942 1,335,736
NW Holdings      
Debt Instrument [Line Items]      
Balance Outstanding 2,518,500 2,448,700 2,242,300
Long-term debt 2,502,400 2,432,800 2,228,200
Less: unamortized debt issuance costs 16,100 15,900 14,100
Long-term debt $ 2,376,700 $ 2,272,200 $ 2,086,700
SiEnergy term loan | SiEnergy      
Debt Instrument [Line Items]      
Weighted average interest rate (as percent) 0.00% 0.00% 6.10%
Long-term debt $ 0 $ 0 $ 148,100
Mortgages | Natural first mortgage bonds | NW Natural      
Debt Instrument [Line Items]      
Balance Outstanding $ 1,544,700 $ 1,544,700 $ 1,374,700
Weighted average interest rate (as percent) 4.70% 4.70% 4.60%
Secured Debt | SiEnergy secured senior notes | SiEnergy      
Debt Instrument [Line Items]      
Balance Outstanding $ 185,000 $ 185,000 $ 0
Weighted average interest rate (as percent) 5.60% 5.60% 0.00%
Secured Debt | NWN Water Term Loan Due 2026 | NWN Water      
Debt Instrument [Line Items]      
Balance Outstanding $ 0 $ 55,000 $ 55,000
Weighted average interest rate (as percent) 0.00% 4.70% 4.70%
Secured Debt | Other water debt | NWN Water      
Debt Instrument [Line Items]      
Balance Outstanding $ 3,800 $ 4,000 $ 4,500
Secured Debt | Term Loan      
Debt Instrument [Line Items]      
Balance Outstanding $ 50,000 $ 50,000 $ 50,000
Weighted average interest rate (as percent) 4.70% 5.20% 5.30%
Unsecured Debt | NWN Water unsecured senior notes      
Debt Instrument [Line Items]      
Balance Outstanding $ 75,000 $ 0 $ 0
Weighted average interest rate (as percent) 5.40% 0.00% 0.00%
Unsecured Debt | NW Holdings Unsecured Senior Bonds      
Debt Instrument [Line Items]      
Balance Outstanding $ 335,000 $ 285,000 $ 285,000
Weighted average interest rate (as percent) 5.70% 5.70% 5.70%
Junior Subordinated Debt | Junior Subordinated Debentures      
Debt Instrument [Line Items]      
Balance Outstanding $ 325,000 $ 325,000 $ 325,000
Weighted average interest rate (as percent) 7.00% 7.00% 7.00%