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Working Capital - Additional Information (Detail) (USD $)
In Millions, unless otherwise specified
9 Months Ended
Feb. 28, 2013
Feb. 29, 2012
May 31, 2012
Working Capital Detail [Line Items]      
Working capital $ 182.5   $ 218.3
Allowances for doubtful receivables 2.9   2.5
Provisions for bad debts 0.9 1.2  
Uncollectible accounts written off 0.5 0.3  
Average Cost
     
Working Capital Detail [Line Items]      
Amount inventory values would be higher by average cost method $ 20.5   $ 22.7