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Summary of Significant Accounting Policies - Schedule of Activity in Allowance for Doubtful Accounts (Detail) - USD ($)
$ in Thousands
12 Months Ended
Apr. 30, 2021
Apr. 30, 2020
Accounts Receivable, Allowance for Credit Loss [Roll Forward]    
Balance at beginning of year $ 606 $ 361
Bad debt provision 53 364
Doubtful accounts written off (net) (23) (119)
Balance at end of year $ 636 $ 606