Guarantees (Details) - USD ($)	3 Months Ended								12 Months Ended
	Jul. 31, 2018	Apr. 30, 2018	Jan. 31, 2018	Oct. 31, 2017	Jul. 31, 2017	Apr. 30, 2017	Jan. 31, 2017	Oct. 31, 2016	Jul. 31, 2018	Jul. 31, 2017	Jul. 31, 2016
Guarantor Obligations [Line Items]
Net sales	$ 724,700,000	$ 700,000,000	$ 664,700,000	$ 644,800,000	$ 660,100,000	$ 608,200,000	$ 550,600,000	$ 553,000,000	$ 2,734,200,000	$ 2,371,900,000	$ 2,220,300,000
Letters of credit contingent liability	8,200,000				10,500,000				8,200,000	10,500,000
Amount drawn on letters of credit	0				0				0	0
Advanced Filtration Systems Inc.
Guarantor Obligations [Line Items]
Long-term debt, carrying value	$ 35,500,000				$ 27,800,000				35,500,000	27,800,000
Equity method investment, equity in earnings									1,300,000	2,100,000	(700,000)
Royalty | Advanced Filtration Systems Inc.
Guarantor Obligations [Line Items]
Net sales									$ 7,000,000	$ 5,900,000	$ 5,100,000