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Summary of Significant Accounting Policies - Summary of Cash and Restricted Cash (Details) - USD ($)
$ in Thousands
Apr. 30, 2019
Apr. 30, 2018
Apr. 30, 2017
Accounting Policies [Abstract]      
Cash $ 3,237 $ 856  
Restricted cash 0 150  
Total cash and restricted cash $ 3,237 $ 1,006 $ 3,445