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Fair Value Measurements - (Details) - USD ($)
$ in Thousands
Jan. 30, 2021
Apr. 30, 2020
Fair Value Measurement    
Available for sale securities $ 53,491 $ 58,095
Recurring basis    
Fair Value Measurement    
Available for sale securities 53,491 58,095
Total 53,491 58,095
Recurring basis | Significant other observable inputs (Level 2)    
Fair Value Measurement    
Available for sale securities 53,491 58,095
Total $ 53,491 $ 58,095