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Organization and Significant Accounting Policies - Contract Estimates (Details) - USD ($)
 12 Months Ended
Apr. 30, 2022
Apr. 30, 2021
Apr. 30, 2020
TMS contract      
Amount of aggregate impact of adjustments in contract estimates on revenue related to performance obligations satisfied or partially satisfied in previous periods $ (1,124,000) $ (1,041,000)  
Amount of revised aggregate impact of adjustments in contract estimates on revenue related to performance obligations satisfied or partially satisfied in previous periods 1,124,000 1,041,000  
Revision of estimate of total costs required to complete the contracts | Cumulative catch-up adjustment | Design and development agreement      
Amount of aggregate impact of adjustments in contract estimates on revenue related to performance obligations satisfied or partially satisfied in previous periods   $ 1,099,000  
Revision of estimate of total costs required to complete the contracts | Cumulative catch-up adjustment | TMS contract      
Amount of aggregate impact of adjustments in contract estimates on revenue related to performance obligations satisfied or partially satisfied in previous periods $ (1,403,000)   $ (1,403,000)