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Basic and Diluted Earnings Per Share - Additional Information (Detail)
In Millions, unless otherwise specified
9 Months Ended 3 Months Ended 9 Months Ended
Jan. 31, 2014
Jan. 31, 2015
Jan. 31, 2015
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]      
Anti-dilutive securities excluded from computation of earnings per share, shares 0.1us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount    
Restricted Stock      
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]      
Anti-dilutive securities excluded from computation of earnings per share, shares   0.5us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount
/ us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis
= us-gaap_RestrictedStockMember
0.5us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount
/ us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis
= us-gaap_RestrictedStockMember