Guarantees (Details) - USD ($)	12 Months Ended
	Jul. 31, 2017	Jul. 31, 2016	Jul. 31, 2015
Guarantor Obligations [Line Items]
Letters of credit contingent liability	$ 10,500,000	$ 7,300,000
Amount drawn on letters of credit	0	0
Advanced Filtration Systems Inc.
Guarantor Obligations [Line Items]
Long-term debt, carrying value	27,800,000	24,800,000
Equity method investment, equity in earnings	2,100,000	(700,000)	$ 2,300,000
Royalty revenue	$ 5,900,000	$ 5,100,000	$ 5,800,000