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Business Segments - Additional Information (Details) $ in Millions | 3 Months Ended | 9 Months Ended |  |
--- | --- | --- | --- | ---
Sep. 30, 2019 USD ($) | Jun. 30, 2019 USD ($) | Sep. 30, 2018 USD ($) | Sep. 30, 2019 USD ($) segment | Sep. 30, 2018 USD ($) | Jun. 03, 2019 USD ($) | Dec. 31, 2018 USD ($)
Restructuring Cost and Reserve [Line Items] |  |  |  |  |  |  |
Gain on asset sales, net | $ 68.2 |  | $ 0.0 | $ 89.8 | $ 0.0 |  |
Number of business segments | segment |  |  |  | 2 |  |  |
Goodwill | 523.8 |  |  | $ 523.8 |  |  | $ 534.7
Gain on the sale of oil and gas rights | 62.4 |  |  | 91.7 |  |  |
Disposal Group, Not Discontinued Operation, Gain (Loss) on Disposal |  |  |  | (1.8) | $ 0.0 |  |
Cast Products |  |  |  |  |  |  |
Restructuring Cost and Reserve [Line Items] |  |  |  |  |  |  |
Disposal Group, Not Discontinued Operation, Gain (Loss) on Disposal | 6.2 |  |  |  |  |  |
Forged Products |  |  |  |  |  |  |
Restructuring Cost and Reserve [Line Items] |  |  |  |  |  |  |
Goodwill |  |  |  |  |  | $ 10.4 |
Disposal Group, Not Discontinued Operation, Gain (Loss) on Disposal | $ (0.4) | $ (7.7) |  | $ (8.1) |  |  |

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