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Working Capital - Additional Information (Detail) (USD $)
In Millions, unless otherwise specified
6 Months Ended
Nov. 30, 2013
Nov. 30, 2012
May 31, 2013
Working Capital Detail [Line Items]      
Working capital $ 190.9   $ 187.3
Allowances for doubtful receivables 3.1   2.3
Provisions for bad debts 1.0 0.4  
Uncollectible accounts written off 0.2 0.2  
Average Cost
     
Working Capital Detail [Line Items]      
Amount inventory values would be higher by average cost method $ 21.0   $ 20.7