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Revenue from contracts with customers Disaggregation of revenue (Details) - USD ($) $ in Thousands | 3 Months Ended | 9 Months Ended
--- | --- | ---
Sep. 30, 2018 | Sep. 30, 2017 | Sep. 30, 2018 | Sep. 30, 2017
Disaggregation of Revenue [Line Items] |  |  |  |
Revenues | $ 1,280,787 | $ 1,272,548 | $ 3,321,678 | $ 3,278,112
Intersegment eliminations |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenues | (7,171) | $ (5,586) | (41,661) | $ (37,581)
Intrasegment eliminations |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenues | (204,040) |  | (363,877) |
Natural gas transportation |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenues | 32,241 |  | 96,609 |
Natural gas gathering |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenues | 2,320 |  | 6,900 |
Natural gas storage |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenues | 2,795 |  | 8,563 |
Contracting services |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenues | 409,006 |  | 730,628 |
Construction materials |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenues | 538,962 |  | 1,100,185 |
Inside specialty contracting |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenues | 217,474 |  | 667,664 |
Outside specialty contracting |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenues | 100,988 |  | 283,432 |
Other |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenues | 18,166 |  | 55,578 |
Revenues from contracts with customers |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenues | 1,265,638 |  | 3,281,257 |
Revenues out of scope |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenues | 15,149 |  | 40,421 |
Residential utility sales |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenues | 75,249 |  | 398,758 |
Commercial utility sales |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenues | 64,433 |  | 289,521 |
Industrial utility sales |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenues | 13,159 |  | 43,191 |
Other utility sales |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenues | 2,056 |  | 5,766 |
Electric |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenues | 86,080 |  | 251,984 |
Electric | Intersegment eliminations |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenues | 0 |  | 0 |
Electric | Other |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenues | 6,158 |  | 22,836 |
Electric | Revenues from contracts with customers |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenues | 84,635 |  | 251,331 |
Electric | Revenues out of scope |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenues | 1,445 |  | 653 |
Electric | Residential utility sales |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenues | 31,424 |  | 93,359 |
Electric | Commercial utility sales |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenues | 36,259 |  | 103,636 |
Electric | Industrial utility sales |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenues | 8,738 |  | 25,734 |
Electric | Other utility sales |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenues | 2,056 |  | 5,766 |
Natural gas distribution |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenues | 92,248 |  | 554,452 |
Natural gas distribution | Intersegment eliminations |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenues | 0 |  | 0 |
Natural gas distribution | Natural gas transportation |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenues | 10,841 |  | 32,104 |
Natural gas distribution | Other |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenues | 3,208 |  | 10,821 |
Natural gas distribution | Revenues from contracts with customers |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenues | 90,469 |  | 551,666 |
Natural gas distribution | Revenues out of scope |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenues | 1,779 |  | 2,786 |
Natural gas distribution | Residential utility sales |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenues | 43,825 |  | 305,399 |
Natural gas distribution | Commercial utility sales |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenues | 28,174 |  | 185,885 |
Natural gas distribution | Industrial utility sales |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenues | 4,421 |  | 17,457 |
Natural gas distribution | Other utility sales |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenues | 0 |  | 0 |
Pipeline and midstream |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenues | 29,071 |  | 61,965 |
Pipeline and midstream | Intersegment eliminations |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenues | (3,187) |  | (31,485) |
Pipeline and midstream | Natural gas transportation |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenues | 21,400 |  | 64,505 |
Pipeline and midstream | Natural gas gathering |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenues | 2,320 |  | 6,900 |
Pipeline and midstream | Natural gas storage |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenues | 2,795 |  | 8,563 |
Pipeline and midstream | Other |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenues | 5,701 |  | 13,353 |
Pipeline and midstream | Revenues from contracts with customers |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenues | 29,029 |  | 61,836 |
Pipeline and midstream | Revenues out of scope |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenues | 42 |  | 129 |
Construction materials and contracting |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenues | 743,763 |  | 1,466,435 |
Construction materials and contracting | Intersegment eliminations |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenues | (165) |  | (501) |
Construction materials and contracting | Intrasegment eliminations |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenues | (204,040) |  | (363,877) |
Construction materials and contracting | Contracting services |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenues | 409,006 |  | 730,628 |
Construction materials and contracting | Construction materials |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenues | 538,962 |  | 1,100,185 |
Construction materials and contracting | Other |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenues | 0 |  | 0 |
Construction materials and contracting | Revenues from contracts with customers |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenues | 743,763 |  | 1,466,435 |
Construction materials and contracting | Revenues out of scope |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenues | 0 |  | 0 |
Construction services |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenues | 329,578 |  | 986,649 |
Construction services | Intersegment eliminations |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenues | (782) |  | (1,332) |
Construction services | Inside specialty contracting |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenues | 217,474 |  | 667,664 |
Construction services | Outside specialty contracting |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenues | 100,988 |  | 283,432 |
Construction services | Other |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenues | 15 |  | 32 |
Construction services | Revenues from contracts with customers |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenues | 317,695 |  | 949,796 |
Construction services | Revenues out of scope |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenues | 11,883 |  | 36,853 |
Other |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenues | 47 |  | 193 |
Other | Intersegment eliminations |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenues | (3,037) |  | (8,343) |
Other | Other |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenues | 3,084 |  | 8,536 |
Other | Revenues from contracts with customers |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenues | 47 |  | 193 |
Other | Revenues out of scope |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenues | $ 0 |  | $ 0 |

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