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Revenue from contracts with customers Disaggregation of revenue (Details) - USD ($) $ in Thousands | 3 Months Ended
--- | ---
Mar. 31, 2018 | Mar. 31, 2017
Disaggregation of Revenue [Line Items] |  |  |
Revenues |  | $ 976,293 | $ 937,925
Intersegment operating revenues |  | 0 | $ 0
Intrasegment eliminations |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenues | [1] | (34,270) |
Other |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenues |  | 18,187 |
Intersegment eliminations |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Intersegment operating revenues |  | (24,509) |
Revenue from contracts with customers |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenues |  | 964,542 |
Revenues out of scope |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenues |  | 11,751 |
Natural gas transportation |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenues |  | 32,997 |
Natural gas gathering |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenues |  | 2,270 |
Natural gas storage |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenues |  | 3,134 |
Contracting services |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenues |  | 74,064 |
Construction materials |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenues |  | 173,591 |
Inside specialty contracting |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenues |  | 233,821 |
Outside specialty contracting |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenues |  | 87,181 |
Residential utility sales |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenues |  | 228,069 |
Commercial utility sales |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenues |  | 151,592 |
Industrial utility sales |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenues |  | 16,579 |
Other utility sales |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenues |  | 1,836 |
Electric |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenues |  | 87,404 |
Electric | Intrasegment eliminations |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenues | [1] | 0 |
Electric | Other |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenues |  | 8,252 |
Electric | Intersegment eliminations |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Intersegment operating revenues |  | 0 |
Electric | Revenue from contracts with customers |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenues |  | 88,742 |
Electric | Revenues out of scope |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenues |  | (1,338) |
Electric | Natural gas transportation |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenues |  | 0 |
Electric | Natural gas gathering |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenues |  | 0 |
Electric | Natural gas storage |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenues |  | 0 |
Electric | Contracting services |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenues |  | 0 |
Electric | Construction materials |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenues |  | 0 |
Electric | Inside specialty contracting |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenues |  | 0 |
Electric | Outside specialty contracting |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenues |  | 0 |
Electric | Residential utility sales |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenues |  | 35,183 |
Electric | Commercial utility sales |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenues |  | 34,701 |
Electric | Industrial utility sales |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenues |  | 8,770 |
Electric | Other utility sales |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenues |  | 1,836 |
Natural gas distribution |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenues |  | 332,664 |
Natural gas distribution | Intrasegment eliminations |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenues | [1] | 0 |
Natural gas distribution | Other |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenues |  | 3,999 |
Natural gas distribution | Intersegment eliminations |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Intersegment operating revenues |  | 0 |
Natural gas distribution | Revenue from contracts with customers |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenues |  | 332,764 |
Natural gas distribution | Revenues out of scope |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenues |  | (100) |
Natural gas distribution | Natural gas transportation |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenues |  | 11,179 |
Natural gas distribution | Natural gas gathering |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenues |  | 0 |
Natural gas distribution | Natural gas storage |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenues |  | 0 |
Natural gas distribution | Contracting services |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenues |  | 0 |
Natural gas distribution | Construction materials |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenues |  | 0 |
Natural gas distribution | Inside specialty contracting |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenues |  | 0 |
Natural gas distribution | Outside specialty contracting |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenues |  | 0 |
Natural gas distribution | Residential utility sales |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenues |  | 192,886 |
Natural gas distribution | Commercial utility sales |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenues |  | 116,891 |
Natural gas distribution | Industrial utility sales |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenues |  | 7,809 |
Natural gas distribution | Other utility sales |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenues |  | 0 |
Pipeline and midstream |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenues |  | 8,833 |
Pipeline and midstream | Intrasegment eliminations |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenues | [1] | 0 |
Pipeline and midstream | Other |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenues |  | 3,326 |
Pipeline and midstream | Intersegment eliminations |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Intersegment operating revenues |  | (21,759) |
Pipeline and midstream | Revenue from contracts with customers |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenues |  | 8,789 |
Pipeline and midstream | Revenues out of scope |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenues |  | 44 |
Pipeline and midstream | Natural gas transportation |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenues |  | 21,818 |
Pipeline and midstream | Natural gas gathering |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenues |  | 2,270 |
Pipeline and midstream | Natural gas storage |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenues |  | 3,134 |
Pipeline and midstream | Contracting services |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenues |  | 0 |
Pipeline and midstream | Construction materials |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenues |  | 0 |
Pipeline and midstream | Inside specialty contracting |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenues |  | 0 |
Pipeline and midstream | Outside specialty contracting |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenues |  | 0 |
Pipeline and midstream | Residential utility sales |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenues |  | 0 |
Pipeline and midstream | Commercial utility sales |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenues |  | 0 |
Pipeline and midstream | Industrial utility sales |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenues |  | 0 |
Pipeline and midstream | Other utility sales |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenues |  | 0 |
Construction materials and contracting |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenues |  | 213,284 |
Construction materials and contracting | Intrasegment eliminations |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenues | [1] | (34,270) |
Construction materials and contracting | Other |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenues |  | 0 |
Construction materials and contracting | Intersegment eliminations |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Intersegment operating revenues |  | (101) |
Construction materials and contracting | Revenue from contracts with customers |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenues |  | 213,284 |
Construction materials and contracting | Revenues out of scope |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenues |  | 0 |
Construction materials and contracting | Natural gas transportation |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenues |  | 0 |
Construction materials and contracting | Natural gas gathering |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenues |  | 0 |
Construction materials and contracting | Natural gas storage |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenues |  | 0 |
Construction materials and contracting | Contracting services |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenues |  | 74,064 |
Construction materials and contracting | Construction materials |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenues |  | 173,591 |
Construction materials and contracting | Inside specialty contracting |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenues |  | 0 |
Construction materials and contracting | Outside specialty contracting |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenues |  | 0 |
Construction materials and contracting | Residential utility sales |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenues |  | 0 |
Construction materials and contracting | Commercial utility sales |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenues |  | 0 |
Construction materials and contracting | Industrial utility sales |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenues |  | 0 |
Construction materials and contracting | Other utility sales |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenues |  | 0 |
Construction services |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenues |  | 334,050 |
Construction services | Intrasegment eliminations |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenues | [1] | 0 |
Construction services | Other |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenues |  | (86) |
Construction services | Intersegment eliminations |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Intersegment operating revenues |  | (11) |
Construction services | Revenue from contracts with customers |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenues |  | 320,905 |
Construction services | Revenues out of scope |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenues |  | 13,145 |
Construction services | Natural gas transportation |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenues |  | 0 |
Construction services | Natural gas gathering |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenues |  | 0 |
Construction services | Natural gas storage |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenues |  | 0 |
Construction services | Contracting services |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenues |  | 0 |
Construction services | Construction materials |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenues |  | 0 |
Construction services | Inside specialty contracting |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenues |  | 233,821 |
Construction services | Outside specialty contracting |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenues |  | 87,181 |
Construction services | Residential utility sales |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenues |  | 0 |
Construction services | Commercial utility sales |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenues |  | 0 |
Construction services | Industrial utility sales |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenues |  | 0 |
Construction services | Other utility sales |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenues |  | 0 |
Other |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenues |  | 58 |
Other | Intrasegment eliminations |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenues | [1] | 0 |
Other | Other |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenues |  | 2,696 |
Other | Intersegment eliminations |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Intersegment operating revenues |  | (2,638) |
Other | Revenue from contracts with customers |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenues |  | 58 |
Other | Revenues out of scope |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenues |  | 0 |
Other | Natural gas transportation |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenues |  | 0 |
Other | Natural gas gathering |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenues |  | 0 |
Other | Natural gas storage |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenues |  | 0 |
Other | Contracting services |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenues |  | 0 |
Other | Construction materials |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenues |  | 0 |
Other | Inside specialty contracting |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenues |  | 0 |
Other | Outside specialty contracting |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenues |  | 0 |
Other | Residential utility sales |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenues |  | 0 |
Other | Commercial utility sales |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenues |  | 0 |
Other | Industrial utility sales |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenues |  | 0 |
Other | Other utility sales |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenues |  | $ 0 |
[1] | Intrasegment revenues are presented within the construction materials and contracting segment to highlight the focus on vertical integration as this segment sells materials to both third parties and internal customers. Due to consolidation requirements, these revenues must be eliminated against construction materials to arrive at the external operating revenue total for the segment.

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