v3.26.1
Segment Information - Schedule of Summarized Financial Information by Segment (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]        
Operating revenues $ 243,552 $ 236,194 $ 733,955 $ 730,478
Depreciation 44,212 41,535 88,346 82,035
Income (loss) from operations 33,157 27,211 196,025 181,565
Interest expense, net (33,352) (30,491) (66,704) (59,886)
Income tax expense (benefit) 610 (940) 33,149 33,587
Parent Company        
Segment Reporting [Line Items]        
Operating revenues 243,552 236,194 733,955 730,478
Depreciation 44,212 41,535 88,346 82,035
Income (loss) from operations 33,157 27,211 196,025 181,565
Interest expense, net 33,352 30,491 66,704 59,886
Income tax expense (benefit) 610 (940) 33,149 33,587
Capital expenditures 121,294 120,480 234,950 222,664
Operating Segments | NW Natural        
Segment Reporting [Line Items]        
Operating revenues 204,802 200,807 638,698 649,620
Depreciation 39,592 36,564 79,036 72,600
Income (loss) from operations 22,939 22,388 166,625 167,420
Interest expense, net 17,426 15,128 35,104 30,708
Income tax expense (benefit) 2,231 1,638 34,386 37,302
Capital expenditures 86,988 93,514 166,603 177,122
Operating Segments | SiEnergy        
Segment Reporting [Line Items]        
Operating revenues 13,546 11,502 45,241 34,168
Depreciation 1,768 2,396 3,565 4,466
Income (loss) from operations 4,897 3,589 18,731 13,202
Interest expense, net 2,607 2,321 5,150 4,578
Income tax expense (benefit) 565 360 3,102 2,304
Capital expenditures 20,938 15,920 45,882 26,445
Operating Segments | NWN Water Utility        
Segment Reporting [Line Items]        
Operating revenues 17,077 16,294 32,046 30,203
Depreciation 2,852 2,575 5,745 4,969
Income (loss) from operations 3,419 4,296 5,818 7,339
Interest expense, net 821 744 1,509 1,536
Income tax expense (benefit) 750 1,053 1,304 1,684
Capital expenditures 13,331 10,939 22,428 18,990
Operating Segments | Other        
Segment Reporting [Line Items]        
Operating revenues 8,127 7,591 17,970 16,487
Depreciation 0 0 0 0
Income (loss) from operations 1,902 (3,062) 4,851 (6,396)
Interest expense, net 12,498 12,298 24,941 23,064
Income tax expense (benefit) (2,936) (3,991) (5,643) (7,703)
Capital expenditures 37 107 37 107
Operating Segments | NWN Gas Utility        
Segment Reporting [Line Items]        
Operating revenues 204,802 200,807 638,698 649,620
Depreciation 39,592 36,564 79,036 72,600
Income (loss) from operations $ 22,939 $ 22,388 $ 166,625 $ 167,420