Fair Value of Financial Instruments (Details) - USD ($) $ in Thousands	Jul. 31, 2021	Apr. 30, 2021
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	$ 85,058	$ 81,720
Marketable securities	16,280	16,006
Total	101,338	97,726
Quoted Prices in Active Markets for Identical Assets (Level 1)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	85,058	81,720
Marketable securities	15,778	15,332
Total	100,836	97,052
Significant Other Observable Inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	0	0
Marketable securities	502	674
Total	502	674
Significant Unobservable Inputs (Level 3)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	0	0
Marketable securities	0	0
Total	$ 0	$ 0