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Disaggregation of revenue (Details) - USD ($) $ in Thousands | 3 Months Ended
--- | ---
Mar. 31, 2021 | Mar. 31, 2020
Disaggregation of Revenue [Line Items] |  |
Operating revenues: | $ 1,227,938 | $ 1,197,373
Intersegment eliminations |  |
Disaggregation of Revenue [Line Items] |  |
Operating revenues: | (30,935) | (31,085)
Intrasegment eliminations |  |
Disaggregation of Revenue [Line Items] |  |
Operating revenues: | (46,716) | (44,104)
Natural gas transportation |  |
Disaggregation of Revenue [Line Items] |  |
Operating revenues: | 41,869 | 39,230
Natural gas gathering |  |
Disaggregation of Revenue [Line Items] |  |
Operating revenues: |  | 2,090
Natural gas storage |  |
Disaggregation of Revenue [Line Items] |  |
Operating revenues: | 4,029 | 3,046
Contracting services |  |
Disaggregation of Revenue [Line Items] |  |
Operating revenues: | 96,025 | 98,401
Construction materials |  |
Disaggregation of Revenue [Line Items] |  |
Operating revenues: | 216,412 | 207,910
Inside specialty contracting |  |
Disaggregation of Revenue [Line Items] |  |
Operating revenues: | 355,190 | 372,209
Outside specialty contracting |  |
Disaggregation of Revenue [Line Items] |  |
Operating revenues: | 151,363 | 130,150
Other |  |
Disaggregation of Revenue [Line Items] |  |
Operating revenues: | 18,819 | 17,531
Revenues from contracts with customers |  |
Disaggregation of Revenue [Line Items] |  |
Operating revenues: | 1,216,016 | 1,183,547
Revenues out of scope |  |
Disaggregation of Revenue [Line Items] |  |
Operating revenues: | 11,922 | 13,826
Residential utility sales |  |
Disaggregation of Revenue [Line Items] |  |
Operating revenues: | 236,573 | 219,050
Commercial utility sales |  |
Disaggregation of Revenue [Line Items] |  |
Operating revenues: | 152,980 | 148,583
Industrial utility sales |  |
Disaggregation of Revenue [Line Items] |  |
Operating revenues: | 18,841 | 18,888
Other utility sales |  |
Disaggregation of Revenue [Line Items] |  |
Operating revenues: | 1,566 | 1,648
Electric |  |
Disaggregation of Revenue [Line Items] |  |
Operating revenues: | 84,673 | 85,908
Electric | Intersegment eliminations |  |
Disaggregation of Revenue [Line Items] |  |
Operating revenues: | (136) | (195)
Electric | Other |  |
Disaggregation of Revenue [Line Items] |  |
Operating revenues: | 9,773 | 8,450
Electric | Revenues from contracts with customers |  |
Disaggregation of Revenue [Line Items] |  |
Operating revenues: | 87,596 | 86,206
Electric | Revenues out of scope |  |
Disaggregation of Revenue [Line Items] |  |
Operating revenues: | (2,923) | (298)
Electric | Residential utility sales |  |
Disaggregation of Revenue [Line Items] |  |
Operating revenues: | 33,436 | 32,349
Electric | Commercial utility sales |  |
Disaggregation of Revenue [Line Items] |  |
Operating revenues: | 32,928 | 33,587
Electric | Industrial utility sales |  |
Disaggregation of Revenue [Line Items] |  |
Operating revenues: | 10,029 | 10,367
Electric | Other utility sales |  |
Disaggregation of Revenue [Line Items] |  |
Operating revenues: | 1,566 | 1,648
Natural gas distribution |  |
Disaggregation of Revenue [Line Items] |  |
Operating revenues: | 350,206 | 326,443
Natural gas distribution | Intersegment eliminations |  |
Disaggregation of Revenue [Line Items] |  |
Operating revenues: | (142) | (185)
Natural gas distribution | Natural gas transportation |  |
Disaggregation of Revenue [Line Items] |  |
Operating revenues: | 12,452 | 11,798
Natural gas distribution | Other |  |
Disaggregation of Revenue [Line Items] |  |
Operating revenues: | 3,009 | 2,498
Natural gas distribution | Revenues from contracts with customers |  |
Disaggregation of Revenue [Line Items] |  |
Operating revenues: | 347,320 | 324,329
Natural gas distribution | Revenues out of scope |  |
Disaggregation of Revenue [Line Items] |  |
Operating revenues: | 2,886 | 2,114
Natural gas distribution | Residential utility sales |  |
Disaggregation of Revenue [Line Items] |  |
Operating revenues: | 203,137 | 186,701
Natural gas distribution | Commercial utility sales |  |
Disaggregation of Revenue [Line Items] |  |
Operating revenues: | 120,052 | 114,996
Natural gas distribution | Industrial utility sales |  |
Disaggregation of Revenue [Line Items] |  |
Operating revenues: | 8,812 | 8,521
Natural gas distribution | Other utility sales |  |
Disaggregation of Revenue [Line Items] |  |
Operating revenues: | 0 | 0
Pipeline |  |
Disaggregation of Revenue [Line Items] |  |
Operating revenues: | 9,913 | 10,655
Pipeline | Intersegment eliminations |  |
Disaggregation of Revenue [Line Items] |  |
Operating revenues: | (26,229) | (25,199)
Pipeline | Natural gas transportation |  |
Disaggregation of Revenue [Line Items] |  |
Operating revenues: | 29,417 | 27,432
Pipeline | Natural gas gathering |  |
Disaggregation of Revenue [Line Items] |  |
Operating revenues: |  | 2,090
Pipeline | Natural gas storage |  |
Disaggregation of Revenue [Line Items] |  |
Operating revenues: | 4,029 | 3,046
Pipeline | Other |  |
Disaggregation of Revenue [Line Items] |  |
Operating revenues: | 2,660 | 3,241
Pipeline | Revenues from contracts with customers |  |
Disaggregation of Revenue [Line Items] |  |
Operating revenues: | 9,877 | 10,610
Pipeline | Revenues out of scope |  |
Disaggregation of Revenue [Line Items] |  |
Operating revenues: | 36 | 45
Construction materials and contracting |  |
Disaggregation of Revenue [Line Items] |  |
Operating revenues: | 265,659 | 262,144
Construction materials and contracting | Intersegment eliminations |  |
Disaggregation of Revenue [Line Items] |  |
Operating revenues: | (62) | (63)
Construction materials and contracting | Intrasegment eliminations |  |
Disaggregation of Revenue [Line Items] |  |
Operating revenues: | (46,716) | (44,104)
Construction materials and contracting | Contracting services |  |
Disaggregation of Revenue [Line Items] |  |
Operating revenues: | 96,025 | 98,401
Construction materials and contracting | Construction materials |  |
Disaggregation of Revenue [Line Items] |  |
Operating revenues: | 216,412 | 207,910
Construction materials and contracting | Other |  |
Disaggregation of Revenue [Line Items] |  |
Operating revenues: | 0 | 0
Construction materials and contracting | Revenues from contracts with customers |  |
Disaggregation of Revenue [Line Items] |  |
Operating revenues: | 265,659 | 262,144
Construction materials and contracting | Revenues out of scope |  |
Disaggregation of Revenue [Line Items] |  |
Operating revenues: | 0 | 0
Construction services |  |
Disaggregation of Revenue [Line Items] |  |
Operating revenues: | 517,470 | 512,205
Construction services | Intersegment eliminations |  |
Disaggregation of Revenue [Line Items] |  |
Operating revenues: | (1,042) | (2,470)
Construction services | Inside specialty contracting |  |
Disaggregation of Revenue [Line Items] |  |
Operating revenues: | 355,190 | 372,209
Construction services | Outside specialty contracting |  |
Disaggregation of Revenue [Line Items] |  |
Operating revenues: | 151,363 | 130,150
Construction services | Other |  |
Disaggregation of Revenue [Line Items] |  |
Operating revenues: | 36 | 351
Construction services | Revenues from contracts with customers |  |
Disaggregation of Revenue [Line Items] |  |
Operating revenues: | 505,547 | 500,240
Construction services | Revenues out of scope |  |
Disaggregation of Revenue [Line Items] |  |
Operating revenues: | 11,923 | 11,965
Other |  |
Disaggregation of Revenue [Line Items] |  |
Operating revenues: | 17 | 18
Other | Intersegment eliminations |  |
Disaggregation of Revenue [Line Items] |  |
Operating revenues: | (3,324) | (2,973)
Other | Other |  |
Disaggregation of Revenue [Line Items] |  |
Operating revenues: | 3,341 | 2,991
Other | Revenues from contracts with customers |  |
Disaggregation of Revenue [Line Items] |  |
Operating revenues: | 17 | 18
Other | Revenues out of scope |  |
Disaggregation of Revenue [Line Items] |  |
Operating revenues: | $ 0 | $ 0

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