Guarantees (Details) (USD $)	3 Months Ended
	Oct. 31, 2014	Oct. 31, 2013
Guarantor Obligations [Line Items]
Contingent liability for standby letters of credit, issued and outstanding	$ 7,900,000
Amount drawn upon letters of credit	0
Advanced Filtration Systems, Inc. [Member]
Guarantor Obligations [Line Items]
Outstanding debt of joint venture	27,100,000
Joint venture investment earnings	900,000	600,000
Royalty income	$ 1,700,000	$ 1,500,000