Deferred Compensation And Retirement Plans - Fair Value Measurements of Defined Benefit Plan Assets (Detail) - Deferred Compensation and Pension Plans - USD ($) $ in Thousands	Apr. 30, 2021	Apr. 30, 2020
Defined Benefit Plan Disclosure [Line Items]
Total defined benefit plan assets	$ 26,746	$ 24,235
Mutual Funds
Defined Benefit Plan Disclosure [Line Items]
Total defined benefit plan assets	26,140	24,041
Money Market Funds
Defined Benefit Plan Disclosure [Line Items]
Total defined benefit plan assets	606	194
Fair Value, Inputs, Level 1
Defined Benefit Plan Disclosure [Line Items]
Total defined benefit plan assets	606	194
Fair Value, Inputs, Level 1 | Money Market Funds
Defined Benefit Plan Disclosure [Line Items]
Total defined benefit plan assets	606	194
Fair Value, Inputs, Level 2
Defined Benefit Plan Disclosure [Line Items]
Total defined benefit plan assets	26,140	24,041
Fair Value, Inputs, Level 2 | Mutual Funds
Defined Benefit Plan Disclosure [Line Items]
Total defined benefit plan assets	$ 26,140	$ 24,041