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Fair Value of Financial Instruments - Summary of Fair Value Hierarchy for Financial Assets and Liabilities Measured Recurring and Nonrecurring Basis (Detail) - USD ($)
$ in Thousands
Jul. 31, 2018
Apr. 30, 2018
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Financial Assets $ 3,670 $ 4,115
Financial Liabilities 4,037 4,467
Trading Securities Held in Non-Qualified Compensation Plans [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Financial Assets 3,605 4,050
Cash Surrender Value of Life Insurance Policies [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Financial Assets 65 65
Non Qualified Compensation Plans [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Financial Liabilities 4,037 4,462
Interest Rate Swap Derivatives [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Financial Liabilities   5
Level 1 [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Financial Assets 3,605 4,050
Level 1 [Member] | Trading Securities Held in Non-Qualified Compensation Plans [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Financial Assets 3,605 4,050
Level 2 [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Financial Assets 65 65
Financial Liabilities 4,037 4,467
Level 2 [Member] | Cash Surrender Value of Life Insurance Policies [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Financial Assets 65 65
Level 2 [Member] | Non Qualified Compensation Plans [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Financial Liabilities $ 4,037 4,462
Level 2 [Member] | Interest Rate Swap Derivatives [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Financial Liabilities   $ 5