Summary of Significant Accounting Policies - Summary of Fair Value Hierarchy for Financial Assets and Liabilities Measured Recurring and Nonrecurring Basis (Detail) (USD $) In Thousands, unless otherwise specified	Apr. 30, 2013	Apr. 30, 2012
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Financial Assets	$ 4,173	$ 3,537
Financial Liabilities	4,743	4,095
Trading securities held in deferred compensation plan [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Financial Assets	4,077	3,454
Cash surrender value of life insurance policies [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Financial Assets	96	83
Deferred compensation plans [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Financial Liabilities	4,399	3,717
Interest rate swap derivative [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Financial Liabilities	344	378
Level 1 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Financial Assets	4,077	3,454
Financial Liabilities
Level 1 [Member] | Trading securities held in deferred compensation plan [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Financial Assets	4,077	3,454
Level 1 [Member] | Cash surrender value of life insurance policies [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Financial Assets
Level 1 [Member] | Deferred compensation plans [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Financial Liabilities
Level 1 [Member] | Interest rate swap derivative [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Financial Liabilities
Level 2 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Financial Assets	96	83
Financial Liabilities	4,743	4,095
Level 2 [Member] | Trading securities held in deferred compensation plan [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Financial Assets
Level 2 [Member] | Cash surrender value of life insurance policies [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Financial Assets	96	83
Level 2 [Member] | Deferred compensation plans [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Financial Liabilities	4,399	3,717
Level 2 [Member] | Interest rate swap derivative [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Financial Liabilities	344	378
Level 3 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Financial Assets
Financial Liabilities
Level 3 [Member] | Trading securities held in deferred compensation plan [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Financial Assets
Level 3 [Member] | Cash surrender value of life insurance policies [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Financial Assets
Level 3 [Member] | Deferred compensation plans [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Financial Liabilities
Level 3 [Member] | Interest rate swap derivative [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Financial Liabilities