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Schedule of Other Current Assets (Parenthetical) (Detail) - USD ($) $ in Millions | Apr. 30, 2018 | Dec. 31, 2017
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Former CEO | Scenario, Forecast |  |
Schedule Of Other Current Assets [Line Items] |  |
Payment advances of lump sum benefit | $ 9.6 |
Rabbi Trust |  |
Schedule Of Other Current Assets [Line Items] |  |
Investments liquidation value |  | $ 8.9

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