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Goodwill and Other Intangible Assets - Additional Information (Detail) - USD ($)
$ in Millions
12 Months Ended
May. 31, 2015
May. 31, 2014
May. 31, 2013
Intangible Assets And Goodwill [Line Items]      
Intangible assets accumulated impairment $ 14.9 $ 14.9  
Intangible asset amortization expense 32.9 $ 28.2 $ 27.7
Future amortization expense of intangible asset in 2016 39.3    
Future amortization expense of intangible asset in 2017 38.9    
Future amortization expense of intangible asset in 2018 37.9    
Future amortization expense of intangible asset in 2019 37.4    
Future amortization expense of intangible asset in 2020 $ 35.4