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Interim Financial Information - Basis of Presentation (Details) - USD ($) $ / shares in Units, $ in Millions | 3 Months Ended | 6 Months Ended
--- | --- | ---
Jun. 30, 2020 | Jun. 30, 2019 | Jun. 30, 2020 | Jun. 30, 2019
Business And Organization [Line Items] |  |  |  |
Out-of-period adjustment | $ 10.6 |  |  |
Net income (loss) | $ 30.2 | $ 49.2 | $ 60.0 | $ 87.9
Diluted earnings (loss) per common share (in dollars per share) | $ 1.63 | $ 2.64 | $ 3.25 | $ 4.73
Restatement Adjustment |  |  |  |
Business And Organization [Line Items] |  |  |  |
Net income (loss) | $ (9.7) |  |  |
Diluted earnings (loss) per common share (in dollars per share) | $ (0.53) |  |  |

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