Guarantees (Details) - USD ($)	3 Months Ended
	Oct. 31, 2018	Oct. 31, 2017	Jul. 31, 2018
Guarantor Obligations [Line Items]
Net sales	$ 701,400,000	$ 644,800,000
Contingent liability for standby letters of credit, issued and outstanding	11,200,000	8,200,000
Amount drawn upon letters of credit	0		$ 0
Advanced Filtration Systems, Inc.
Guarantor Obligations [Line Items]
Outstanding debt of joint venture	35,800,000
Joint venture investment earnings (loss)	(300,000)	100,000
Royalty | Advanced Filtration Systems, Inc.
Guarantor Obligations [Line Items]
Net sales	$ 1,700,000	$ 1,900,000