Fair Value Measurements of Defined Benefit Plan Assets (Detail) - Deferred Compensation and Pension Plans - USD ($) $ in Thousands	Apr. 30, 2018	Apr. 30, 2017
Defined Benefit Plan Disclosure [Line Items]
Total defined benefit plan assets	$ 26,090	$ 25,446
Mutual Funds
Defined Benefit Plan Disclosure [Line Items]
Total defined benefit plan assets	25,899	25,446
Money Market Funds
Defined Benefit Plan Disclosure [Line Items]
Total defined benefit plan assets	191
Fair Value, Inputs, Level 1
Defined Benefit Plan Disclosure [Line Items]
Total defined benefit plan assets	191
Fair Value, Inputs, Level 1 | Money Market Funds
Defined Benefit Plan Disclosure [Line Items]
Total defined benefit plan assets	191
Fair Value, Inputs, Level 2
Defined Benefit Plan Disclosure [Line Items]
Total defined benefit plan assets	25,899	25,446
Fair Value, Inputs, Level 2 | Mutual Funds
Defined Benefit Plan Disclosure [Line Items]
Total defined benefit plan assets	$ 25,899	$ 25,446