Valuation and Qualifying Accounts and Reserves (Details) - USD ($)	12 Months Ended
	Jul. 31, 2021	Jul. 31, 2020	Jul. 31, 2019	Jul. 31, 2018
Allowance for doubtful accounts receivable
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at beginning of period	$ 1,648,000	$ 1,769,000	$ 1,867,000	$ 1,761,000
Charged to cost and expenses	(18,000)	45,000	1,136,000
Charged to other accounts	215,000	0	0
Transfers (deductions)	(318,000)	(143,000)	(1,030,000)
Balance at end of period	1,648,000	1,769,000	1,867,000
Inventory reserves
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at beginning of period	20,229,000	19,076,000	19,696,000	17,427,000
Charged to cost and expenses	4,364,000	1,647,000	6,015,000
Charged to other accounts	0	0	0
Transfers (deductions)	(3,211,000)	(2,267,000)	(3,746,000)
Balance at end of period	20,229,000	19,076,000	19,696,000
Valuation allowance for deferred tax assets
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at beginning of period	28,384,000	11,471,000	12,568,000	$ 11,854,000
Charged to cost and expenses	17,750,000	750,000	58,000
Charged to other accounts	0	0	656,000
Transfers (deductions)	(837,000)	(1,847,000)	0
Balance at end of period	$ 28,384,000	$ 11,471,000	$ 12,568,000