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Summary of Significant Accounting Policies - Cash Equivalents Table (Details) - USD ($)
$ in Thousands
Apr. 30, 2021
Apr. 30, 2020
Apr. 30, 2019
Accounting Policies [Abstract]      
Cash and cash equivalents $ 5,206 $ 4,365  
Restricted cash 525 850  
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents $ 5,731 $ 5,215 $ 11,156