Valuation and Qualifying Accounts and Reserves (Details) - USD ($)	12 Months Ended
	Jul. 31, 2020	Jul. 31, 2019	Jul. 31, 2018	Jul. 31, 2017
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Estimated contract settlement costs	$ 444,000	$ 6,351,000	$ 0
Allowance for doubtful accounts receivable
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at beginning of period	1,769,000	1,867,000	1,761,000	$ 1,300,000
Charged to cost and expenses	45,000	1,136,000	573,000
Charged to other accounts - describe	0	0	0
Transfers (deductions) - describe	(143,000)	(1,030,000)	(112,000)
Balance at end of period	1,769,000	1,867,000	1,761,000
Estimated contract settlement costs	476,000
Inventory reserves
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at beginning of period	19,076,000	19,696,000	17,427,000	16,019,000
Charged to cost and expenses	1,647,000	6,015,000	5,628,000
Charged to other accounts - describe	0	0	0
Transfers (deductions) - describe	(2,267,000)	(3,746,000)	(4,220,000)
Balance at end of period	19,076,000	19,696,000	17,427,000
Valuation allowance for deferred tax assets
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at beginning of period	11,471,000	12,568,000	11,854,000	$ 8,633,000
Charged to cost and expenses	750,000	58,000	3,221,000
Charged to other accounts - describe	0	656,000	0
Transfers (deductions) - describe	(1,847,000)	0	0
Balance at end of period	$ 11,471,000	$ 12,568,000	$ 11,854,000