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Summary of Significant Accounting Policies - Schedule of Property Plant and Equipment (Detail) - USD ($)
$ in Thousands
12 Months Ended
Apr. 30, 2021
Apr. 30, 2020
Property, Plant and Equipment [Line Items]    
Property plant and equipment gross $ 58,804 $ 57,859
Less accumulated depreciation (42,822) (41,587)
Net property, plant and equipment 15,982 16,272
Land    
Property, Plant and Equipment [Line Items]    
Property plant and equipment gross 41 41
Building and improvements    
Property, Plant and Equipment [Line Items]    
Property plant and equipment gross $ 17,017 $ 16,920
Building and improvements | Minimum    
Property, Plant and Equipment [Line Items]    
Useful Life (in years) 10 years 10 years
Building and improvements | Maximum    
Property, Plant and Equipment [Line Items]    
Useful Life (in years) 40 years 40 years
Machinery and equipment    
Property, Plant and Equipment [Line Items]    
Property plant and equipment gross $ 41,746 $ 40,898
Machinery and equipment | Minimum    
Property, Plant and Equipment [Line Items]    
Useful Life (in years) 5 years 5 years
Machinery and equipment | Maximum    
Property, Plant and Equipment [Line Items]    
Useful Life (in years) 10 years 10 years