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, 2018	Apr. 30, 2017
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Financial Assets	$ 4,115	$ 3,823
Financial Liabilities	4,467	4,248
Trading Securities Held in Non-Qualified Compensation Plans [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Financial Assets	4,050	3,748
Cash Surrender Value of Life Insurance Policies [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Financial Assets	65	75
Non Qualified Compensation Plans [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Financial Liabilities	4,462	4,186
Interest Rate Swap Derivatives [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Financial Liabilities	5	62
Level 1 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Financial Assets	4,050	3,748
Level 1 [Member] | Trading Securities Held in Non-Qualified Compensation Plans [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Financial Assets	4,050	3,748
Level 2 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Financial Assets	65	75
Financial Liabilities	4,467	4,248
Level 2 [Member] | Cash Surrender Value of Life Insurance Policies [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Financial Assets	65	75
Level 2 [Member] | Non Qualified Compensation Plans [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Financial Liabilities	4,462	4,186
Level 2 [Member] | Interest Rate Swap Derivatives [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Financial Liabilities	$ 5	$ 62