Accounts Receivable (Details) - USD ($)	12 Months Ended
	Jul. 31, 2020	Jul. 31, 2019
Statement [Line Items]
Total accounts receivable	$ 128,585,000	$ 146,899,000
Less: Allowance for doubtful accounts	1,769,000	1,867,000
Accounts receivable, net	$ 126,816,000	$ 145,032,000
Accounts Receivable | Customer Concentration Risk | U.S. government
Statement [Line Items]
Concentration risk, percentage	31.00%	27.80%
Billed Receivables | Commercial and International Customers
Statement [Line Items]
Total accounts receivable	$ 67,109,000	$ 85,556,000
Billed Receivables | U.S. Government and Its Agencies
Statement [Line Items]
Total accounts receivable	32,870,000	38,856,000
Unbilled Receivables | Commercial and International Customers
Statement [Line Items]
Total accounts receivable	21,588,000	20,469,000
Unbilled Receivables | U.S. Government and Its Agencies
Statement [Line Items]
Total accounts receivable	$ 7,018,000	$ 2,018,000