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Revenue Recognition - Summary of Net Sales Transferred to Customers at a Point in Time and Over Time (Detail) - USD ($)
$ in Thousands
3 Months Ended
Jul. 31, 2019
Jul. 31, 2018
Disaggregation of Revenue [Line Items]    
Net sales transferred to customers $ 39,336 $ 42,152
Over Time    
Disaggregation of Revenue [Line Items]    
Net sales transferred to customers 38,284 40,330
Point in Time    
Disaggregation of Revenue [Line Items]    
Net sales transferred to customers 1,052 1,822
Domestic    
Disaggregation of Revenue [Line Items]    
Net sales transferred to customers 29,287 36,070
Domestic | Over Time    
Disaggregation of Revenue [Line Items]    
Net sales transferred to customers 28,235 34,248
Domestic | Point in Time    
Disaggregation of Revenue [Line Items]    
Net sales transferred to customers 1,052 1,822
International    
Disaggregation of Revenue [Line Items]    
Net sales transferred to customers 10,049 6,082
International | Over Time    
Disaggregation of Revenue [Line Items]    
Net sales transferred to customers 10,049 6,082
International | Point in Time    
Disaggregation of Revenue [Line Items]    
Net sales transferred to customers $ 0 $ 0