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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 9 Months Ended
Jan. 31, 2019
Jan. 31, 2018
Jan. 31, 2019
Jan. 31, 2018
Disaggregation of Revenue [Line Items]        
Net sales transferred to customers $ 32,372 $ 38,190 $ 111,802 $ 113,542
Over Time        
Disaggregation of Revenue [Line Items]        
Net sales transferred to customers 31,569   106,866  
Point in Time        
Disaggregation of Revenue [Line Items]        
Net sales transferred to customers 803   4,936  
Domestic        
Disaggregation of Revenue [Line Items]        
Net sales transferred to customers 25,217   91,909  
Domestic | Over Time        
Disaggregation of Revenue [Line Items]        
Net sales transferred to customers 24,414   86,973  
Domestic | Point in Time        
Disaggregation of Revenue [Line Items]        
Net sales transferred to customers 803   4,936  
International        
Disaggregation of Revenue [Line Items]        
Net sales transferred to customers 7,155   19,893  
International | Over Time        
Disaggregation of Revenue [Line Items]        
Net sales transferred to customers 7,155   19,893  
International | Point in Time        
Disaggregation of Revenue [Line Items]        
Net sales transferred to customers $ 0   $ 0