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Long-lived Assets - Impairments, Held for Sale or Disposals - Narrative (Details) - USD ($) $ in Millions |  | 3 Months Ended | 12 Months Ended
--- | --- | --- | ---
Jun. 29, 2020 | Sep. 30, 2020 | Dec. 31, 2018 | Dec. 31, 2020 | Dec. 31, 2019 | Dec. 31, 2018
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items] |  |  |  |  |  |
Impairment of assets |  |  |  | $ 5.6 | $ 49.7 | $ 268.0
Impairment of assets related to materials & construction |  | $ 5.6 |  |  |  |
Goodwill |  |  | $ (65.1) | (10.5) | $ (15.4) | (65.1)
Port Allen Solar Power Facility assets | Not Discontinued Operations |  |  |  |  |  |
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items] |  |  |  |  |  |
Purchase consideration upon disposal |  | 17.1 |  |  |  |
Net gain (loss) on disposal |  | $ 8.9 |  |  |  |
GPRM Prestress, LLC | Held for sale |  |  |  |  |  |
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items] |  |  |  |  |  |
Ownership interest sold | 51.00% |  |  |  | 51.00% |
GPRM Prestress, LLC | Not Discontinued Operations |  |  |  |  |  |
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items] |  |  |  |  |  |
Purchase consideration upon disposal | $ 5.0 |  |  |  |  |
Net gain (loss) on disposal | $ (0.1) |  |  |  |  |
Materials and Construction Segment |  |  |  |  |  |
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items] |  |  |  |  |  |
Goodwill |  |  | (56.4) | (1.8) | $ (6.7) | (56.4)
Commercial property |  |  |  |  |  |
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items] |  |  |  |  |  |
Goodwill |  |  | (8.7) | $ (8.7) | $ (8.7) | $ (8.7)
Paving and Quarry Assets | Materials and Construction Segment |  |  |  |  |  |
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items] |  |  |  |  |  |
Impairment of assets |  |  | $ 40.6 |  |  |
Paving and Quarry Assets | Materials and Construction Segment | Weighted average discount rate |  |  |  |  |  |
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items] |  |  |  |  |  |
Weighted average discount rate (percent) |  |  |  |  | 13.50% |

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