v3.26.1
Revenue from contracts with customers - Schedule of 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]        
Revenues from contracts with customers $ 372,921 $ 348,678 $ 972,234 $ 1,026,697
Other revenues 2,382 2,508 9,046 (678)
Total external operating revenues 375,303 351,186 981,280 1,026,019
Total reportable segment operating revenues        
Disaggregation of Revenue [Line Items]        
Total external operating revenues 385,565 361,215 1,026,258 1,069,656
Intersegment eliminations        
Disaggregation of Revenue [Line Items]        
Revenues from contracts with customers (10,463) (10,208) (45,378) (43,995)
Total external operating revenues (10,463) (10,208) (45,378) (43,995)
Natural gas transportation        
Disaggregation of Revenue [Line Items]        
Revenues from contracts with customers 64,007 61,934 130,590 128,897
Natural gas storage        
Disaggregation of Revenue [Line Items]        
Revenues from contracts with customers 5,530 5,172 10,997 11,202
Other        
Disaggregation of Revenue [Line Items]        
Revenues from contracts with customers 34,233 33,905 79,750 76,514
Residential utility sales        
Disaggregation of Revenue [Line Items]        
Revenues from contracts with customers 141,081 128,610 426,808 457,530
Commercial utility sales        
Disaggregation of Revenue [Line Items]        
Revenues from contracts with customers 116,911 109,127 323,463 349,935
Industrial utility sales        
Disaggregation of Revenue [Line Items]        
Revenues from contracts with customers 19,539 18,345 41,961 42,971
Other utility sales        
Disaggregation of Revenue [Line Items]        
Revenues from contracts with customers 2,083 1,793 4,043 3,643
Electric | Total reportable segment operating revenues        
Disaggregation of Revenue [Line Items]        
Revenues from contracts with customers 117,064 100,020 239,716 216,609
Other revenues (1,148) (2,134) (2,782) (6,462)
Total external operating revenues 115,916 97,886 236,934 210,147
Electric | Intersegment eliminations        
Disaggregation of Revenue [Line Items]        
Revenues from contracts with customers (124) (140) (291) (318)
Total external operating revenues (124) (140) (291) (318)
Electric | Natural gas transportation | Total reportable segment operating revenues        
Disaggregation of Revenue [Line Items]        
Revenues from contracts with customers 0 0 0 0
Electric | Natural gas storage | Total reportable segment operating revenues        
Disaggregation of Revenue [Line Items]        
Revenues from contracts with customers 0 0 0 0
Electric | Other | Total reportable segment operating revenues        
Disaggregation of Revenue [Line Items]        
Revenues from contracts with customers 18,600 17,123 40,864 34,714
Electric | Residential utility sales | Total reportable segment operating revenues        
Disaggregation of Revenue [Line Items]        
Revenues from contracts with customers 35,080 28,569 74,481 68,254
Electric | Commercial utility sales | Total reportable segment operating revenues        
Disaggregation of Revenue [Line Items]        
Revenues from contracts with customers 50,479 43,428 99,663 91,905
Electric | Industrial utility sales | Total reportable segment operating revenues        
Disaggregation of Revenue [Line Items]        
Revenues from contracts with customers 10,946 9,247 20,956 18,411
Electric | Other utility sales | Total reportable segment operating revenues        
Disaggregation of Revenue [Line Items]        
Revenues from contracts with customers 2,083 1,793 4,043 3,643
Natural gas distribution | Total reportable segment operating revenues        
Disaggregation of Revenue [Line Items]        
Revenues from contracts with customers 209,145 202,186 663,218 740,306
Other revenues 3,502 4,608 11,776 5,735
Total external operating revenues 212,647 206,794 674,994 746,041
Natural gas distribution | Intersegment eliminations        
Disaggregation of Revenue [Line Items]        
Revenues from contracts with customers (86) (92) (175) (187)
Total external operating revenues (86) (92) (175) (187)
Natural gas distribution | Natural gas transportation | Total reportable segment operating revenues        
Disaggregation of Revenue [Line Items]        
Revenues from contracts with customers 16,834 15,814 34,340 33,524
Natural gas distribution | Natural gas storage | Total reportable segment operating revenues        
Disaggregation of Revenue [Line Items]        
Revenues from contracts with customers 0 0 0 0
Natural gas distribution | Other | Total reportable segment operating revenues        
Disaggregation of Revenue [Line Items]        
Revenues from contracts with customers 11,371 11,626 31,921 35,103
Natural gas distribution | Residential utility sales | Total reportable segment operating revenues        
Disaggregation of Revenue [Line Items]        
Revenues from contracts with customers 106,001 100,041 352,327 389,276
Natural gas distribution | Commercial utility sales | Total reportable segment operating revenues        
Disaggregation of Revenue [Line Items]        
Revenues from contracts with customers 66,432 65,699 223,800 258,030
Natural gas distribution | Industrial utility sales | Total reportable segment operating revenues        
Disaggregation of Revenue [Line Items]        
Revenues from contracts with customers 8,593 9,098 21,005 24,560
Natural gas distribution | Other utility sales | Total reportable segment operating revenues        
Disaggregation of Revenue [Line Items]        
Revenues from contracts with customers 0 0 0 0
Pipeline | Total reportable segment operating revenues        
Disaggregation of Revenue [Line Items]        
Revenues from contracts with customers 46,712 46,473 69,300 69,782
Other revenues 28 34 52 49
Total external operating revenues 46,740 46,507 69,352 69,831
Pipeline | Intersegment eliminations        
Disaggregation of Revenue [Line Items]        
Revenues from contracts with customers (10,052) (9,796) (44,512) (43,132)
Total external operating revenues (10,052) (9,796) (44,512) (43,132)
Pipeline | Natural gas transportation | Total reportable segment operating revenues        
Disaggregation of Revenue [Line Items]        
Revenues from contracts with customers 47,173 46,120 96,250 95,373
Pipeline | Natural gas storage | Total reportable segment operating revenues        
Disaggregation of Revenue [Line Items]        
Revenues from contracts with customers 5,530 5,172 10,997 11,202
Pipeline | Other | Total reportable segment operating revenues        
Disaggregation of Revenue [Line Items]        
Revenues from contracts with customers 4,061 4,977 6,565 6,339
Pipeline | Residential utility sales | Total reportable segment operating revenues        
Disaggregation of Revenue [Line Items]        
Revenues from contracts with customers 0 0 0 0
Pipeline | Commercial utility sales | Total reportable segment operating revenues        
Disaggregation of Revenue [Line Items]        
Revenues from contracts with customers 0 0 0 0
Pipeline | Industrial utility sales | Total reportable segment operating revenues        
Disaggregation of Revenue [Line Items]        
Revenues from contracts with customers 0 0 0 0
Pipeline | Other utility sales | Total reportable segment operating revenues        
Disaggregation of Revenue [Line Items]        
Revenues from contracts with customers 0 0 0 0
Other | Total reportable segment operating revenues        
Disaggregation of Revenue [Line Items]        
Revenues from contracts with customers 0 (1) 0 0
Other revenues 0 0 0 0
Total external operating revenues 0 (1) 0 0
Other | Intersegment eliminations        
Disaggregation of Revenue [Line Items]        
Revenues from contracts with customers (201) (180) (400) (358)
Total external operating revenues (201) (180) (400) (358)
Other | Natural gas transportation | Total reportable segment operating revenues        
Disaggregation of Revenue [Line Items]        
Revenues from contracts with customers 0 0 0 0
Other | Natural gas storage | Total reportable segment operating revenues        
Disaggregation of Revenue [Line Items]        
Revenues from contracts with customers 0 0 0 0
Other | Other | Total reportable segment operating revenues        
Disaggregation of Revenue [Line Items]        
Revenues from contracts with customers 201 179 400 358
Other | Residential utility sales | Total reportable segment operating revenues        
Disaggregation of Revenue [Line Items]        
Revenues from contracts with customers 0 0 0 0
Other | Commercial utility sales | Total reportable segment operating revenues        
Disaggregation of Revenue [Line Items]        
Revenues from contracts with customers 0 0 0 0
Other | Industrial utility sales | Total reportable segment operating revenues        
Disaggregation of Revenue [Line Items]        
Revenues from contracts with customers 0 0 0 0
Other | Other utility sales | Total reportable segment operating revenues        
Disaggregation of Revenue [Line Items]        
Revenues from contracts with customers $ 0 $ 0 $ 0 $ 0