Fair Value Measurements of Defined Benefit Plan Assets (Detail) $ in Thousands	Apr. 30, 2016 USD ($)
Defined Benefit Plan Disclosure [Line Items]
Total defined benefit plan assets	$ 24,867
Mutual Funds
Defined Benefit Plan Disclosure [Line Items]
Total defined benefit plan assets	7,990
Defined Benefit Plan Common Stock
Defined Benefit Plan Disclosure [Line Items]
Total defined benefit plan assets	7,910
Corporate Bonds And Municipal Bonds
Defined Benefit Plan Disclosure [Line Items]
Total defined benefit plan assets	5,597
US Treasury and Government
Defined Benefit Plan Disclosure [Line Items]
Total defined benefit plan assets	2,055
Money Market Funds
Defined Benefit Plan Disclosure [Line Items]
Total defined benefit plan assets	1,315
Fair Value, Inputs, Level 1
Defined Benefit Plan Disclosure [Line Items]
Total defined benefit plan assets	17,215
Fair Value, Inputs, Level 1 | Mutual Funds
Defined Benefit Plan Disclosure [Line Items]
Total defined benefit plan assets	7,990
Fair Value, Inputs, Level 1 | Defined Benefit Plan Common Stock
Defined Benefit Plan Disclosure [Line Items]
Total defined benefit plan assets	7,910
Fair Value, Inputs, Level 1 | Money Market Funds
Defined Benefit Plan Disclosure [Line Items]
Total defined benefit plan assets	1,315
Fair Value, Inputs, Level 2
Defined Benefit Plan Disclosure [Line Items]
Total defined benefit plan assets	7,652
Fair Value, Inputs, Level 2 | Corporate Bonds And Municipal Bonds
Defined Benefit Plan Disclosure [Line Items]
Total defined benefit plan assets	5,597
Fair Value, Inputs, Level 2 | US Treasury and Government
Defined Benefit Plan Disclosure [Line Items]
Total defined benefit plan assets	$ 2,055