Guarantees (Details) - USD ($)	3 Months Ended
	Oct. 31, 2015	Oct. 31, 2014
Guarantor Obligations [Line Items]
Contingent liability for standby letters of credit, issued and outstanding	$ 7,800,000
Amount drawn upon letters of credit	0
Advanced Filtration Systems, Inc. [Member]
Guarantor Obligations [Line Items]
Outstanding debt of joint venture	25,500,000
Joint venture investment earnings (loss)	(1,200,000)	$ 900,000
Royalty income	$ 1,800,000	$ 1,700,000