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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, 2017
Apr. 30, 2016
Apr. 30, 2015
Accounting Policies [Abstract]      
Beginning Balance $ 8,403 $ 8,653 $ 7,565
Warranties issued and adjustments to provisions 3,769 2,546 4,292
Changes related to preexisting product recall accruals (2,437)    
Warranties assumed in acquisition 228    
Warranty claims (4,419) (2,796) (3,204)
Ending Balance $ 5,544 $ 8,403 $ 8,653