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Share-Based Payments - Valuation Assumptions for Stock Options (Details)
3 Months Ended 6 Months Ended
Oct. 31, 2021
Oct. 31, 2020
Oct. 31, 2021
Oct. 31, 2020
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]        
Expected term (in years) 0 years 6 years    
Risk free interest rate (in percent) 0.00% 0.27%    
Risk-free interest rates minimum (in percent)     0.82% 0.27%
Risk-free interest rates maximum (in percent)     0.00% 0.39%
Volatility rate minimum (in percent) 0.00%   65.94% 72.64%
Volatility Rate maximum (in percent)     66.21% 72.83%
Volatility (in percent)   72.83%    
Dividend yield 0.00% 0.00% 0.00% 0.00%
Minimum        
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]        
Expected term (in years)     6 years  
Maximum        
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]        
Expected term (in years)     6 years