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Stock Options and Stock Appreciation Rights Award Activity (Detail) (Stock Appreciation Rights (Sars) [Member])
3 Months Ended 6 Months Ended
Oct. 31, 2012
Oct. 31, 2011
Oct. 31, 2012
Oct. 31, 2011
Stock Appreciation Rights (Sars) [Member]
       
Stock Option [Line Items]        
Outstanding options and SARS excluded 733,375 733,375 733,375 382,875