Guarantees (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jan. 31, 2019	Jan. 31, 2018	Jan. 31, 2019	Jan. 31, 2018	Jul. 31, 2018
Guarantor Obligations [Line Items]
Net sales	$ 703,700,000	$ 664,700,000	$ 1,405,100,000	$ 1,309,500,000
Contingent liability for standby letters of credit, issued and outstanding	11,200,000		11,200,000		$ 8,200,000
Amount drawn upon letters of credit	0		0		$ 0
Advanced Filtration Systems, Inc.
Guarantor Obligations [Line Items]
Outstanding debt of joint venture	36,800,000		36,800,000
Advanced Filtration Systems, Inc.
Guarantor Obligations [Line Items]
Joint venture investment earnings (loss)	(100,000)	400,000	(300,000)	500,000
Advanced Filtration Systems, Inc. | Royalty
Guarantor Obligations [Line Items]
Net sales	$ 1,600,000	$ 1,700,000	$ 3,300,000	$ 3,600,000