Annual report pursuant to Section 13 and 15(d)

Fair Value Measurements of Defined Benefit Plan Assets (Detail)

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Fair Value Measurements of Defined Benefit Plan Assets (Detail) - Deferred Compensation and Pension Plans - USD ($)
$ in Thousands
Apr. 30, 2017
Apr. 30, 2016
Defined Benefit Plan Disclosure [Line Items]    
Total defined benefit plan assets $ 25,446 $ 24,867
Mutual Funds    
Defined Benefit Plan Disclosure [Line Items]    
Total defined benefit plan assets 25,446 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 25,446 7,652
Fair Value, Inputs, Level 2 | Mutual Funds    
Defined Benefit Plan Disclosure [Line Items]    
Total defined benefit plan assets $ 25,446  
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