v3.26.1
Revenue - Disaggregation of Revenue (Details) - USD ($)
$ in Thousands
 3 Months Ended 6 Months Ended
Jun. 30, 2026
Jun. 30, 2025
Jun. 30, 2026
Jun. 30, 2025
Disaggregation of Revenue [Line Items]        
Revenue from contract with customer, including assessed tax $ 213,565 $ 209,789 $ 674,169 $ 694,198
Revenues 243,552 236,194 733,955 730,478
Natural gas sales | Transferred over Time        
Disaggregation of Revenue [Line Items]        
Revenue from contract with customer, including assessed tax 181,312 179,126 610,185 633,211
Gas storage revenue, net | Transferred over Time        
Disaggregation of Revenue [Line Items]        
Revenue from contract with customer, including assessed tax 4,839 4,082 9,204 8,698
Asset management revenue, net | Transferred over Time        
Disaggregation of Revenue [Line Items]        
Revenue from contract with customer, including assessed tax 1,045 1,545 2,792 3,294
Water and wastewater revenue | Transferred over Time        
Disaggregation of Revenue [Line Items]        
Revenue from contract with customer, including assessed tax 17,077 16,294 32,046 30,203
Gas appliance retail revenue | Transferred at Point in Time        
Disaggregation of Revenue [Line Items]        
Revenue from contract with customer, including assessed tax 825 891 2,134 2,263
Renewable natural gas sales | Transferred over Time        
Disaggregation of Revenue [Line Items]        
Revenue from contract with customer, including assessed tax 7,594 6,890 16,059 14,616
Other revenue | Transferred over Time        
Disaggregation of Revenue [Line Items]        
Revenue from contract with customer, including assessed tax 873 961 1,749 1,913
Alternative revenue        
Disaggregation of Revenue [Line Items]        
Revenues 25,537 22,102 50,883 27,671
Leasing revenue        
Disaggregation of Revenue [Line Items]        
Operating leases 4,450 4,303 8,903 8,609
Operating Segments | NW Natural | NW Natural        
Disaggregation of Revenue [Line Items]        
Revenue from contract with customer, including assessed tax 175,069 174,402 582,485 613,340
Revenues 204,802 200,807 638,698 649,620
Operating Segments | NW Natural | NW Natural | Natural gas sales | Transferred over Time        
Disaggregation of Revenue [Line Items]        
Revenue from contract with customer, including assessed tax 167,487 166,923 566,606 597,172
Operating Segments | NW Natural | NW Natural | Gas storage revenue, net | Transferred over Time        
Disaggregation of Revenue [Line Items]        
Revenue from contract with customer, including assessed tax 4,839 4,082 9,204 8,698
Operating Segments | NW Natural | NW Natural | Asset management revenue, net | Transferred over Time        
Disaggregation of Revenue [Line Items]        
Revenue from contract with customer, including assessed tax 1,045 1,545 2,792 3,294
Operating Segments | NW Natural | NW Natural | Water and wastewater revenue | Transferred over Time        
Disaggregation of Revenue [Line Items]        
Revenue from contract with customer, including assessed tax 0 0 0 0
Operating Segments | NW Natural | NW Natural | Gas appliance retail revenue | Transferred at Point in Time        
Disaggregation of Revenue [Line Items]        
Revenue from contract with customer, including assessed tax 825 891 2,134 2,263
Operating Segments | NW Natural | NW Natural | Renewable natural gas sales | Transferred over Time        
Disaggregation of Revenue [Line Items]        
Revenue from contract with customer, including assessed tax 0 0 0 0
Operating Segments | NW Natural | NW Natural | Other revenue | Transferred over Time        
Disaggregation of Revenue [Line Items]        
Revenue from contract with customer, including assessed tax 873 961 1,749 1,913
Operating Segments | NW Natural | NW Natural | Alternative revenue        
Disaggregation of Revenue [Line Items]        
Revenues 25,283 22,102 47,310 27,671
Operating Segments | NW Natural | NW Natural | Leasing revenue        
Disaggregation of Revenue [Line Items]        
Operating leases 4,450 4,303 8,903 8,609
Operating Segments | SiEnergy | SiEnergy        
Disaggregation of Revenue [Line Items]        
Revenue from contract with customer, including assessed tax 13,292 11,502 41,668 34,168
Revenues 13,546 11,502 45,241 34,168
Operating Segments | SiEnergy | SiEnergy | Natural gas sales | Transferred over Time        
Disaggregation of Revenue [Line Items]        
Revenue from contract with customer, including assessed tax 13,292 11,502 41,668 34,168
Operating Segments | SiEnergy | SiEnergy | Gas storage revenue, net | Transferred over Time        
Disaggregation of Revenue [Line Items]        
Revenue from contract with customer, including assessed tax 0 0 0 0
Operating Segments | SiEnergy | SiEnergy | Asset management revenue, net | Transferred over Time        
Disaggregation of Revenue [Line Items]        
Revenue from contract with customer, including assessed tax 0 0 0 0
Operating Segments | SiEnergy | SiEnergy | Water and wastewater revenue | Transferred over Time        
Disaggregation of Revenue [Line Items]        
Revenue from contract with customer, including assessed tax 0 0 0 0
Operating Segments | SiEnergy | SiEnergy | Gas appliance retail revenue | Transferred at Point in Time        
Disaggregation of Revenue [Line Items]        
Revenue from contract with customer, including assessed tax 0 0 0 0
Operating Segments | SiEnergy | SiEnergy | Renewable natural gas sales | Transferred over Time        
Disaggregation of Revenue [Line Items]        
Revenue from contract with customer, including assessed tax 0 0 0 0
Operating Segments | SiEnergy | SiEnergy | Other revenue | Transferred over Time        
Disaggregation of Revenue [Line Items]        
Revenue from contract with customer, including assessed tax 0 0 0 0
Operating Segments | SiEnergy | SiEnergy | Alternative revenue        
Disaggregation of Revenue [Line Items]        
Revenues 254 0 3,573 0
Operating Segments | SiEnergy | SiEnergy | Leasing revenue        
Disaggregation of Revenue [Line Items]        
Operating leases 0 0 0 0
Operating Segments | NWN Water Utility        
Disaggregation of Revenue [Line Items]        
Revenues 17,077 16,294 32,046 30,203
Operating Segments | NWN Water Utility | NWN Water Utility        
Disaggregation of Revenue [Line Items]        
Revenue from contract with customer, including assessed tax 17,077 16,294    
Revenues 17,077 16,294    
Operating Segments | NWN Water Utility | NWN Water Utility | Natural gas sales | Transferred over Time        
Disaggregation of Revenue [Line Items]        
Revenue from contract with customer, including assessed tax 0 0    
Operating Segments | NWN Water Utility | NWN Water Utility | Gas storage revenue, net | Transferred over Time        
Disaggregation of Revenue [Line Items]        
Revenue from contract with customer, including assessed tax 0 0    
Operating Segments | NWN Water Utility | NWN Water Utility | Asset management revenue, net | Transferred over Time        
Disaggregation of Revenue [Line Items]        
Revenue from contract with customer, including assessed tax 0 0    
Operating Segments | NWN Water Utility | NWN Water Utility | Water and wastewater revenue | Transferred over Time        
Disaggregation of Revenue [Line Items]        
Revenue from contract with customer, including assessed tax 17,077 16,294    
Operating Segments | NWN Water Utility | NWN Water Utility | Gas appliance retail revenue | Transferred at Point in Time        
Disaggregation of Revenue [Line Items]        
Revenue from contract with customer, including assessed tax 0 0    
Operating Segments | NWN Water Utility | NWN Water Utility | Renewable natural gas sales | Transferred over Time        
Disaggregation of Revenue [Line Items]        
Revenue from contract with customer, including assessed tax 0 0    
Operating Segments | NWN Water Utility | NWN Water Utility | Other revenue | Transferred over Time        
Disaggregation of Revenue [Line Items]        
Revenue from contract with customer, including assessed tax 0 0    
Operating Segments | NWN Water Utility | NWN Water Utility | Alternative revenue        
Disaggregation of Revenue [Line Items]        
Revenues 0 0    
Operating Segments | NWN Water Utility | NWN Water Utility | Leasing revenue        
Disaggregation of Revenue [Line Items]        
Operating leases 0 0    
Operating Segments | Other        
Disaggregation of Revenue [Line Items]        
Revenues 8,127 7,591 17,970 16,487
Operating Segments | Other | Other        
Disaggregation of Revenue [Line Items]        
Revenue from contract with customer, including assessed tax 8,127 7,591 17,970 16,487
Revenues 8,127 7,591 17,970 16,487
Operating Segments | Other | Other | Natural gas sales | Transferred over Time        
Disaggregation of Revenue [Line Items]        
Revenue from contract with customer, including assessed tax 533 701 1,911 1,871
Operating Segments | Other | Other | Gas storage revenue, net | Transferred over Time        
Disaggregation of Revenue [Line Items]        
Revenue from contract with customer, including assessed tax 0 0 0 0
Operating Segments | Other | Other | Asset management revenue, net | Transferred over Time        
Disaggregation of Revenue [Line Items]        
Revenue from contract with customer, including assessed tax 0 0 0 0
Operating Segments | Other | Other | Water and wastewater revenue | Transferred over Time        
Disaggregation of Revenue [Line Items]        
Revenue from contract with customer, including assessed tax 0 0 0 0
Operating Segments | Other | Other | Gas appliance retail revenue | Transferred at Point in Time        
Disaggregation of Revenue [Line Items]        
Revenue from contract with customer, including assessed tax 0 0 0 0
Operating Segments | Other | Other | Renewable natural gas sales | Transferred over Time        
Disaggregation of Revenue [Line Items]        
Revenue from contract with customer, including assessed tax 7,594 6,890 16,059 14,616
Operating Segments | Other | Other | Other revenue | Transferred over Time        
Disaggregation of Revenue [Line Items]        
Revenue from contract with customer, including assessed tax 0 0 0 0
Operating Segments | Other | Other | Alternative revenue        
Disaggregation of Revenue [Line Items]        
Revenues 0 0 0 0
Operating Segments | Other | Other | Leasing revenue        
Disaggregation of Revenue [Line Items]        
Operating leases $ 0 $ 0 0 0
Operating Segments | NWN Water | NWN Water        
Disaggregation of Revenue [Line Items]        
Revenue from contract with customer, including assessed tax     32,046 30,203
Revenues     32,046 30,203
Operating Segments | NWN Water | NWN Water | Natural gas sales | Transferred over Time        
Disaggregation of Revenue [Line Items]        
Revenue from contract with customer, including assessed tax     0 0
Operating Segments | NWN Water | NWN Water | Gas storage revenue, net | Transferred over Time        
Disaggregation of Revenue [Line Items]        
Revenue from contract with customer, including assessed tax     0 0
Operating Segments | NWN Water | NWN Water | Asset management revenue, net | Transferred over Time        
Disaggregation of Revenue [Line Items]        
Revenue from contract with customer, including assessed tax     0 0
Operating Segments | NWN Water | NWN Water | Water and wastewater revenue | Transferred over Time        
Disaggregation of Revenue [Line Items]        
Revenue from contract with customer, including assessed tax     32,046 30,203
Operating Segments | NWN Water | NWN Water | Gas appliance retail revenue | Transferred at Point in Time        
Disaggregation of Revenue [Line Items]        
Revenue from contract with customer, including assessed tax     0 0
Operating Segments | NWN Water | NWN Water | Renewable natural gas sales | Transferred over Time        
Disaggregation of Revenue [Line Items]        
Revenue from contract with customer, including assessed tax     0 0
Operating Segments | NWN Water | NWN Water | Other revenue | Transferred over Time        
Disaggregation of Revenue [Line Items]        
Revenue from contract with customer, including assessed tax     0 0
Operating Segments | NWN Water | NWN Water | Alternative revenue        
Disaggregation of Revenue [Line Items]        
Revenues     0 0
Operating Segments | NWN Water | NWN Water | Leasing revenue        
Disaggregation of Revenue [Line Items]        
Operating leases     $ 0 $ 0