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Earnings Per Share - Additional Information (Detail) (Stock Options [Member])
3 Months Ended 9 Months Ended
Jan. 31, 2015
Jan. 31, 2014
Jan. 31, 2015
Jan. 31, 2014
Stock Options [Member]
       
Earnings Per Share [Line Items]        
Anti-dilutive options excluded from computation of earnings per share 70,800us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount
/ us-gaap_AwardTypeAxis
= us-gaap_EmployeeStockOptionMember
36,600us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount
/ us-gaap_AwardTypeAxis
= us-gaap_EmployeeStockOptionMember
70,800us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount
/ us-gaap_AwardTypeAxis
= us-gaap_EmployeeStockOptionMember
36,600us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount
/ us-gaap_AwardTypeAxis
= us-gaap_EmployeeStockOptionMember