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Quarterly Results of Operations - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Millions | 3 Months Ended | 12 Months Ended
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Dec. 31, 2017 | Dec. 31, 2017
Quarterly Financial Information [Line Items] |  |
Provisional Income tax expense | $ 81.8 | $ 81.8
Provisional Income tax expense, reduce earnings per share | $ 0.47 |

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