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Guarantees (Narrative) (Details) - USD ($)	12 Months Ended
Guarantees (Narrative) (Details) - USD ($)	Jul. 31, 2022	Jul. 31, 2021	Jul. 31, 2020
Guarantor Obligations
Investment earnings	$ 1,700,000	$ 4,200,000	$ 5,200,000
Advanced Filtration Systems Inc.
Guarantor Obligations
Investment earnings	8,100,000	8,700,000
Unsecured revolving credit facility
Guarantor Obligations
Available credit facilities	63,000,000
Multi-currency revolving credit facility
Guarantor Obligations
Available credit facilities	17,000,000
Advanced Filtration Systems Inc.
Guarantor Obligations
AFSI outstanding debt (the Company guarantees half)	$ 68,800,000	$ 37,800,000