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Significant Accounting Policies - Change in Accrued Warranties Recorded as Non-Current Liability (Detail) - USD ($)
$ in Thousands
12 Months Ended
Apr. 30, 2018
Apr. 30, 2017
Accounting Policies [Abstract]    
Beginning Balance $ 5,544 $ 8,403
Warranties issued and adjustments to provisions 5,834 3,769
Changes related to preexisting product recall accruals   (2,437)
Warranties assumed in acquisition   228
Warranty claims (3,865) (4,419)
Ending Balance $ 7,513 $ 5,544