Guarantees (Details) - USD ($)	3 Months Ended								12 Months Ended
	Jul. 31, 2019	Apr. 30, 2019	Jan. 31, 2019	Oct. 31, 2018	Jul. 31, 2018	Apr. 30, 2018	Jan. 31, 2018	Oct. 31, 2017	Jul. 31, 2019	Jul. 31, 2018	Jul. 31, 2017
Guarantor Obligations [Line Items]
Net sales	$ 726,900,000	$ 712,800,000	$ 703,700,000	$ 701,400,000	$ 724,700,000	$ 700,000,000	$ 664,700,000	$ 644,800,000	$ 2,844,900,000	$ 2,734,200,000	$ 2,371,900,000
Letters of credit contingent liability	11,000,000				8,200,000				11,000,000	8,200,000
Amount drawn on letters of credit	0				0				0	0
Advanced Filtration Systems Inc.
Guarantor Obligations [Line Items]
Long-term debt, carrying value	$ 38,800,000				$ 35,500,000				38,800,000	35,500,000
Equity method investment, equity in earnings (losses)									(300,000)	1,300,000	2,100,000
Royalty | Advanced Filtration Systems Inc.
Guarantor Obligations [Line Items]
Net sales									$ 6,500,000	$ 7,000,000	$ 5,900,000