v3.26.1
Segment Information - Additional Segment Information (Details) - USD ($)
$ in Thousands
 3 Months Ended 6 Months Ended
Jun. 30, 2026
Jun. 30, 2025
Jun. 30, 2026
Jun. 30, 2025
Segment Reporting [Line Items]        
Total operating revenues $ 243,552 $ 236,194 $ 733,955 $ 730,478
Less: Cost of gas 61,753 64,503 219,902 237,494
Environmental remediation 2,431 2,296 8,756 8,549
General taxes 12,216 12,076 28,559 27,847
Depreciation 44,212 41,535 88,346 82,035
Other operating expenses 1,029 1,225 2,404 2,552
NW Natural income from operations 33,157 27,211 196,025 181,565
Operating Segments | NWN Gas Utility        
Segment Reporting [Line Items]        
Distribution revenues 192,851 189,120 614,085 625,028
Regulated gas storage 10,081 9,251 19,687 19,035
Other revenue 1,870 2,436 4,926 5,557
Total operating revenues 204,802 200,807 638,698 649,620
Less: Cost of gas 53,326 56,939 193,470 216,375
Environmental remediation 2,431 2,296 8,756 8,549
Revenue taxes 7,906 7,832 24,943 26,397
NW Natural margin 141,139 133,740 411,529 398,299
Operations and maintenance 66,515 63,039 137,045 130,805
General taxes 11,641 11,234 27,678 26,213
Depreciation 39,592 36,564 79,036 72,600
Other operating expenses 452 515 1,145 1,261
NW Natural income from operations 22,939 22,388 166,625 167,420
Operating Segments | SiEnergy        
Segment Reporting [Line Items]        
Distribution revenues 13,546 11,502 45,241 34,168
Total operating revenues 13,546 11,502 45,241 34,168
Less: Cost of gas 3,382 2,977 15,661 11,280
Revenue taxes 377 364 1,338 1,143
NW Natural margin 9,787 8,161 28,242 21,745
Operations and maintenance 2,818 1,912 5,632 3,594
General taxes 304 264 314 483
Depreciation 1,768 2,396 3,565 4,466
NW Natural income from operations 4,897 3,589 18,731 13,202
Operating Segments | NWN Water Utility        
Segment Reporting [Line Items]        
Total operating revenues 17,077 16,294 32,046 30,203
Operations and maintenance 9,843 8,068 18,450 15,333
Depreciation 2,852 2,575 5,745 4,969
Other operating expenses 963 1,355 2,033 2,562
NW Natural income from operations $ 3,419 $ 4,296 $ 5,818 $ 7,339