XML 31 R52.htm IDEA: XBRL DOCUMENT v3.2.0.727
Retirement Benefits - Additional Information (Detail) - USD ($)
12 Months Ended
Apr. 30, 2015
Apr. 30, 2014
Apr. 30, 2013
Defined Benefit Plan Disclosure [Line Items]      
Average annual compensation period Ten years    
Defined pension benefit plan, net periodic benefit cost $ 1,180,000    
Employer contributions 775,000 $ 300,000  
Anticipated contribution in the next fiscal year related to pension plans $ 60,000    
Age limit of employees to be eligible for contribution 21 years    
Minimum service period of employees to be eligible for contribution 3 months    
Matching contributions by company 100.00%    
Employee's compensation 3.00%    
Companies matching contribution equal to employee's contributions 50.00%    
Non-matching contribution for participants employed 1.00%    
Contribution made by company $ 834,000 674,000 $ 659,000
Maximum [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Employee's compensation 5.00%    
Contributions by employer per employee's compensation maximum 4.00%    
Minimum [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Employee's compensation 3.00%    
Yield Curve Technique [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Increase decrease in the discount rate 1.00%    
Decrease increase pension expense $ 176,000 181,000  
Yield Curve Technique [Member] | Pension Plan [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Par amount outstanding $ 250,000,000    
Return on Investment Method [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Increase decrease in the discount rate 1.00%    
Decrease increase pension expense $ 160,000 $ 151,000  
Return on Investment Method [Member] | Equity Securities [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Defined benefit plan, Plan asset percentage 70.00% 70.00%  
Return on Investment Method [Member] | Fixed Income Securities [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Defined benefit plan, Plan asset percentage 30.00% 30.00%