Fair Value of Financial Instruments (Details) - USD ($) $ in Thousands	Jan. 31, 2021	Apr. 30, 2020
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	$ 79,759	$ 75,256
Marketable securities	14,052	14,862
Total	93,811	90,118
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	79,759	75,256
Marketable securities	13,369	11,758
Total	93,128	87,014
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	683	3,104
Total	683	3,104
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