Guarantees (Details) - USD ($)	3 Months Ended		9 Months Ended
	Apr. 30, 2016	Apr. 30, 2015	Apr. 30, 2016	Apr. 30, 2015
Guarantor Obligations [Line Items]
Contingent liability for standby letters of credit, issued and outstanding	$ 7,800,000		$ 7,800,000
Amount drawn upon letters of credit	0		0
Advanced Filtration Systems, Inc.
Guarantor Obligations [Line Items]
Outstanding debt of joint venture	23,900,000		23,900,000
Joint venture investment earnings (loss)	200,000	$ 500,000	(1,000,000)	$ 1,900,000
Royalty income	$ 1,300,000	$ 1,500,000	$ 3,900,000	$ 4,600,000