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Summary of Significant Accounting Policies - Summary of Fair Value Hierarchy for Financial Assets and Liabilities Measured Recurring and Nonrecurring Basis (Detail) - USD ($)
$ in Thousands
Apr. 30, 2015
Apr. 30, 2014
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Financial Assets $ 3,730 $ 3,401
Financial Liabilities 4,322 3,892
Trading Securities Held in Non-Qualified Compensation Plans [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Financial Assets 3,683 3,313
Cash Surrender Value of Life Insurance Policies [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Financial Assets 47 88
Non Qualified Compensation Plans [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Financial Liabilities 4,119 3,681
Interest Rate Swap Derivatives [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Financial Liabilities 203 211
Level 1 [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Financial Assets 3,683 3,313
Level 1 [Member] | Trading Securities Held in Non-Qualified Compensation Plans [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Financial Assets 3,683 3,313
Level 2 [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Financial Assets 47 88
Financial Liabilities 4,322 3,892
Level 2 [Member] | Cash Surrender Value of Life Insurance Policies [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Financial Assets 47 88
Level 2 [Member] | Non Qualified Compensation Plans [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Financial Liabilities 4,119 3,681
Level 2 [Member] | Interest Rate Swap Derivatives [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Financial Liabilities $ 203 $ 211