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Financial Instruments - Additional Information (Detail) - USD ($) $ in Millions |  | 12 Months Ended |
--- | --- | --- | ---
Dec. 16, 2019 | Apr. 30, 2020 | Apr. 30, 2019 | Apr. 30, 2018 | Mar. 31, 2017
Financial Instrument [Line Items] |  |  |  |  |
Sale/maturities of available-for-sale marketable securities |  | $ 4.8 |  |  |
Designated as Hedge Instrument | Interest Rate Swap | Cash Flow Hedge |  |  |  |  |
Financial Instrument [Line Items] |  |  |  |  |
Derivative notional amount |  |  |  |  | $ 129.8
Interest rate |  | 1.919% |  |  |
Interest expense recognized on termination of interest rate swap | $ 0.5 |  |  |  |
Not Designated as Hedge Instrument | Foreign Exchange Forward Contracts |  |  |  |  |
Financial Instrument [Line Items] |  |  |  |  |
Foreign currency gains (losses) |  | $ (0.3) | $ 1.2 | $ (3.7) |
Not Designated as Hedge Instrument | Foreign Exchange Forward Contracts | Income Taxes And Other Receivables | Derivatives Purchased |  |  |  |  |
Financial Instrument [Line Items] |  |  |  |  |
Derivative notional amount |  | 91.2 | 51.4 |  |
Not Designated as Hedge Instrument | Foreign Exchange Forward Contracts | Income Taxes And Other Receivables | Derivatives Sold |  |  |  |  |
Financial Instrument [Line Items] |  |  |  |  |
Derivative notional amount |  | $ 41.8 | 40.0 |  |
Available-for-sale Marketable Securities | Minimum |  |  |  |  |
Financial Instrument [Line Items] |  |  |  |  |
Marketable securities remaining maturity |  | 1 month |  |  |
Available-for-sale Marketable Securities | Maximum |  |  |  |  |
Financial Instrument [Line Items] |  |  |  |  |
Marketable securities remaining maturity |  | 12 months |  |  |
Mutual Funds |  |  |  |  |
Financial Instrument [Line Items] |  |  |  |  |
Unrealized loss relates to equity securities |  | $ 8.2 | $ 4.7 |  |
Unrealized gains relates to equity securities |  |  |  | $ 3.9 |

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- Definition Financial Instrument [Line Items] + References No definition available. + Details
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- Definition Interest expense recognized on termination of interest rate swap. + References No definition available. + Details
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- Definition Fixed interest rate related to the interest rate derivative. + References No definition available. + Details
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- Definition Amount of realized and unrealized gain (loss) of derivative instruments not designated or qualifying as hedging instruments. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 50 -Paragraph 4CC -URI http://asc.fasb.org/extlink&oid=109980867&loc=SL109998890-113959 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 50 -Paragraph 4C -Subparagraph (e) -URI http://asc.fasb.org/extlink&oid=109980867&loc=SL5624171-113959 + Details
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