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Financial Instruments - Summary of Gains and Losses on Interest Rate Swap (Detail) - Interest Rate Swap - USD ($)
$ in Thousands
12 Months Ended
Apr. 30, 2018
Apr. 30, 2017
Derivative [Line Items]    
Gains (Losses) recognized in other comprehensive income (net of tax effects of $828 and ($406), respectively) $ 1,465 $ (635)
Losses reclassified from accumulated other comprehensive income into interest (expense) income, net $ (730) $ (94)