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Guarantees (Details) (USD $)
In Millions, unless otherwise specified
3 Months Ended
Oct. 31, 2013
Oct. 31, 2012
Guarantor Obligations [Line Items]    
Contingent liability for standby letters of credit, issued and outstanding $ 8.8  
Advanced Filtration Systems, Inc. [Member]
   
Guarantor Obligations [Line Items]    
Outstanding debt of joint venture 28.9  
Joint venture investment earnings 0.6 0.7
Royalty income $ 1.5 $ 1.6