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Goodwill rollforward (Details) - USD ($) $ in Thousands | 9 Months Ended | 12 Months Ended
--- | --- | ---
Sep. 30, 2021 | Sep. 30, 2020 | Dec. 31, 2020
Goodwill [Roll Forward] |  |  |
Balance at beginning of period | $ 714,963 | $ 681,358 | $ 681,358
Goodwill acquired during the year | 2,900 | 30,919 | 33,214
Measurement period adjustments | (217) | 400 | 391
Balance at end of period | 717,646 | 712,677 | 714,963
Natural gas distribution |  |  |
Goodwill [Roll Forward] |  |  |
Balance at beginning of period | 345,736 | 345,736 | 345,736
Goodwill acquired during the year | 0 | 0 | 0
Measurement period adjustments | 0 | 0 | 0
Balance at end of period | 345,736 | 345,736 | 345,736
Construction materials and contracting |  |  |
Goodwill [Roll Forward] |  |  |
Balance at beginning of period | 226,003 | 217,234 | 217,234
Goodwill acquired during the year | 2,900 | 6,483 | 8,778
Measurement period adjustments | (217) | 0 | (9)
Balance at end of period | 228,686 | 223,717 | 226,003
Construction services |  |  |
Goodwill [Roll Forward] |  |  |
Balance at beginning of period | 143,224 | 118,388 | 118,388
Goodwill acquired during the year | 0 | 24,436 | 24,436
Measurement period adjustments | 0 | 400 | 400
Balance at end of period | $ 143,224 | $ 143,224 | $ 143,224

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- Definition Amount after accumulated impairment loss of an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-03(10)(1)) -URI http://asc.fasb.org/extlink&oid=120398452&loc=d3e534808-122878 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 350 -SubTopic 20 -Section 45 -Paragraph 5 -URI http://asc.fasb.org/extlink&oid=120320667&loc=SL49117168-202975 Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 350 -SubTopic 20 -Section 45 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=99380562&loc=d3e13770-109266 + Details
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- Definition Amount of increase in asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized resulting from a business combination. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 350 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=121556970&loc=d3e13816-109267 + Details
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- Definition Amount of increase (decrease) from adjustments after acquisition date under purchase accounting of an asset representing the future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 805 -SubTopic 10 -Section 25 -Paragraph 16 -URI http://asc.fasb.org/extlink&oid=116868678&loc=d3e961-128460 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 350 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (g) -URI http://asc.fasb.org/extlink&oid=121556970&loc=d3e13816-109267 + Details
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- Definition A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period. + References No definition available. + Details
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- Details
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