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Disaggregation of revenue (Details) - USD ($) $ in Thousands | 3 Months Ended | 12 Months Ended
--- | --- | ---
Dec. 31, 2020 | Sep. 30, 2020 | Jun. 30, 2020 | Mar. 31, 2020 | Dec. 31, 2019 | Sep. 30, 2019 | Jun. 30, 2019 | Mar. 31, 2019 | Dec. 31, 2020 | Dec. 31, 2019 | Dec. 31, 2018
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Operating revenues | $ 1,385,160 | $ 1,587,289 | $ 1,362,928 | $ 1,197,373 | $ 1,378,213 | $ 1,563,799 | $ 1,303,573 | $ 1,091,191 | $ 5,532,750 | $ 5,336,776 | $ 4,531,552
Intersegment eliminations |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Operating revenues |  |  |  |  |  |  |  |  | (76,969) | (77,149) | (64,307)
Intrasegment eliminations |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Operating revenues |  |  |  |  |  |  |  |  | (550,815) | (525,749) | (465,969)
Natural gas transportation |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Operating revenues |  |  |  |  |  |  |  |  | 157,232 | 147,114 | 132,397
Natural gas gathering |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Operating revenues |  |  |  |  |  |  |  |  | 4,865 | 9,164 | 9,159
Natural gas storage |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Operating revenues |  |  |  |  |  |  |  |  | 14,918 | 11,708 | 11,543
Contracting services |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Operating revenues |  |  |  |  |  |  |  |  | 1,069,665 | 1,088,633 | 968,755
Construction materials |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Operating revenues |  |  |  |  |  |  |  |  | 1,659,152 | 1,627,833 | 1,423,068
Inside specialty contracting |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Operating revenues |  |  |  |  |  |  |  |  | 1,397,124 | 1,266,196 | 926,875
Outside specialty contracting |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Operating revenues |  |  |  |  |  |  |  |  | 649,486 | 531,882 | 392,544
Other |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Operating revenues |  |  |  |  |  |  |  |  | 68,865 | 82,669 | 76,796
Revenues from contracts with customers |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Operating revenues |  |  |  |  |  |  |  |  | 5,471,545 | 5,281,621 | 4,469,761
Revenues out of scope |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Operating revenues |  |  |  |  |  |  |  |  | 61,205 | 55,155 | 61,791
Residential utility sales |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Operating revenues |  |  |  |  |  |  |  |  | 599,051 | 608,821 | 579,436
Commercial utility sales |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Operating revenues |  |  |  |  |  |  |  |  | 409,350 | 438,431 | 412,952
Industrial utility sales |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Operating revenues |  |  |  |  |  |  |  |  | 62,987 | 64,660 | 58,956
Other utility sales |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Operating revenues |  |  |  |  |  |  |  |  | 6,634 | 7,408 | 7,556
Electric |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Operating revenues |  |  |  |  |  |  |  |  | 331,538 | 351,725 | 335,123
Electric | Intersegment eliminations |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Operating revenues |  |  |  |  |  |  |  |  | (491) | 0 | 0
Electric | Other |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Operating revenues |  |  |  |  |  |  |  |  | 32,452 | 35,574 | 31,568
Electric | Revenues from contracts with customers |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Operating revenues |  |  |  |  |  |  |  |  | 329,479 | 347,712 | 331,190
Electric | Revenues out of scope |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Operating revenues |  |  |  |  |  |  |  |  | 2,059 | 4,013 | 3,933
Electric | Residential utility sales |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Operating revenues |  |  |  |  |  |  |  |  | 122,663 | 125,369 | 121,477
Electric | Commercial utility sales |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Operating revenues |  |  |  |  |  |  |  |  | 131,477 | 141,596 | 136,236
Electric | Industrial utility sales |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Operating revenues |  |  |  |  |  |  |  |  | 36,744 | 37,765 | 34,353
Electric | Other utility sales |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Operating revenues |  |  |  |  |  |  |  |  | 6,634 | 7,408 | 7,556
Natural gas distribution |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Operating revenues |  |  |  |  |  |  |  |  | 847,651 | 865,222 | 823,247
Natural gas distribution | Intersegment eliminations |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Operating revenues |  |  |  |  |  |  |  |  | (534) | 0 | 0
Natural gas distribution | Natural gas transportation |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Operating revenues |  |  |  |  |  |  |  |  | 45,546 | 45,449 | 43,238
Natural gas distribution | Other |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Operating revenues |  |  |  |  |  |  |  |  | 10,753 | 12,726 | 14,579
Natural gas distribution | Revenues from contracts with customers |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Operating revenues |  |  |  |  |  |  |  |  | 836,269 | 865,357 | 817,095
Natural gas distribution | Revenues out of scope |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Operating revenues |  |  |  |  |  |  |  |  | 11,382 | (135) | 6,152
Natural gas distribution | Residential utility sales |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Operating revenues |  |  |  |  |  |  |  |  | 476,388 | 483,452 | 457,959
Natural gas distribution | Commercial utility sales |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Operating revenues |  |  |  |  |  |  |  |  | 277,873 | 296,835 | 276,716
Natural gas distribution | Industrial utility sales |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Operating revenues |  |  |  |  |  |  |  |  | 26,243 | 26,895 | 24,603
Natural gas distribution | Other utility sales |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Operating revenues |  |  |  |  |  |  |  |  | 0 | 0 | 0
Pipeline |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Operating revenues |  |  |  |  |  |  |  |  | 85,346 | 84,192 | 78,018
Pipeline | Intersegment eliminations |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Operating revenues |  |  |  |  |  |  |  |  | (58,531) | (56,252) | (50,905)
Pipeline | Natural gas transportation |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Operating revenues |  |  |  |  |  |  |  |  | 111,686 | 101,665 | 89,159
Pipeline | Natural gas gathering |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Operating revenues |  |  |  |  |  |  |  |  | 4,865 | 9,164 | 9,159
Pipeline | Natural gas storage |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Operating revenues |  |  |  |  |  |  |  |  | 14,918 | 11,708 | 11,543
Pipeline | Other |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Operating revenues |  |  |  |  |  |  |  |  | 12,216 | 17,687 | 18,865
Pipeline | Revenues from contracts with customers |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Operating revenues |  |  |  |  |  |  |  |  | 85,154 | 83,972 | 77,821
Pipeline | Revenues out of scope |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Operating revenues |  |  |  |  |  |  |  |  | 192 | 220 | 197
Construction materials and contracting |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Operating revenues |  |  |  |  |  |  |  |  | 2,177,585 | 2,189,651 | 1,925,185
Construction materials and contracting | Intersegment eliminations |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Operating revenues |  |  |  |  |  |  |  |  | (417) | (1,066) | (669)
Construction materials and contracting | Intrasegment eliminations |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Operating revenues |  |  |  |  |  |  |  |  | (550,815) | (525,749) | (465,969)
Construction materials and contracting | Contracting services |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Operating revenues |  |  |  |  |  |  |  |  | 1,069,665 | 1,088,633 | 968,755
Construction materials and contracting | Construction materials |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Operating revenues |  |  |  |  |  |  |  |  | 1,659,152 | 1,627,833 | 1,423,068
Construction materials and contracting | Other |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Operating revenues |  |  |  |  |  |  |  |  | 0 | 0 | 0
Construction materials and contracting | Revenues from contracts with customers |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Operating revenues |  |  |  |  |  |  |  |  | 2,177,585 | 2,189,651 | 1,925,185
Construction materials and contracting | Revenues out of scope |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Operating revenues |  |  |  |  |  |  |  |  | 0 | 0 | 0
Construction services |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Operating revenues |  |  |  |  |  |  |  |  | 2,090,685 | 1,845,896 | 1,369,772
Construction services | Intersegment eliminations |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Operating revenues |  |  |  |  |  |  |  |  | (5,038) | (3,370) | (1,681)
Construction services | Inside specialty contracting |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Operating revenues |  |  |  |  |  |  |  |  | 1,397,124 | 1,266,196 | 926,875
Construction services | Outside specialty contracting |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Operating revenues |  |  |  |  |  |  |  |  | 649,486 | 531,882 | 392,544
Construction services | Other |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Operating revenues |  |  |  |  |  |  |  |  | 1,541 | 131 | 525
Construction services | Revenues from contracts with customers |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Operating revenues |  |  |  |  |  |  |  |  | 2,043,113 | 1,794,839 | 1,318,263
Construction services | Revenues out of scope |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Operating revenues |  |  |  |  |  |  |  |  | 47,572 | 51,057 | 51,509
Other |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Operating revenues |  |  |  |  |  |  |  |  | (55) | 90 | 207
Other | Intersegment eliminations |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Operating revenues |  |  |  |  |  |  |  |  | (11,958) | (16,461) | (11,052)
Other | Other |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Operating revenues |  |  |  |  |  |  |  |  | 11,903 | 16,551 | 11,259
Other | Revenues from contracts with customers |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Operating revenues |  |  |  |  |  |  |  |  | (55) | 90 | 207
Other | Revenues out of scope |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Operating revenues |  |  |  |  |  |  |  |  | $ 0 | $ 0 | $ 0

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