Guarantees (Details) - USD ($)	3 Months Ended
	Oct. 31, 2016	Oct. 31, 2015
Guarantor Obligations [Line Items]
Contingent liability for standby letters of credit, issued and outstanding	$ 9,100,000
Amount drawn upon letters of credit	0
Advanced Filtration Systems, Inc.
Guarantor Obligations [Line Items]
Outstanding debt of joint venture	25,800,000
Joint venture investment earnings (loss)	600,000	$ 1,200,000
Royalty income	$ 1,300,000	$ 1,800,000