Annual report pursuant to Section 13 and 15(d)

Financial Instruments - Summary of Gains and Losses on Interest Rate Swap (Parenthetical) (Detail)

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Financial Instruments - Summary of Gains and Losses on Interest Rate Swap (Parenthetical) (Detail) - USD ($)
$ in Thousands
12 Months Ended
Apr. 30, 2020
Apr. 30, 2019
Apr. 30, 2018
Interest Rate Swap      
Derivative [Line Items]      
Gains (Losses) recognized in OCI, tax effects $ (238) $ (281) $ 828