Summary of Quarterly Financial Information - Summary of Unaudited Financial Data (Parenthetical) (Detail) - USD ($) $ in Millions |
3 Months Ended | 12 Months Ended |
|---|---|---|
Dec. 31, 2017 |
Dec. 31, 2017 |
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| Valuation And Qualifying Accounts [Abstract] | ||
| Provisional tax expense due to impact of Tax Act | $ 99.9 | $ 99.9 |
| X | ||||||||||
- Definition Tax cuts and jobs act of 2017 incomplete accounting provisional income tax expense (benefit). No definition available.
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| X | ||||||||||
- References No definition available.
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