Accounts Receivable (Details) - USD ($)	Jan. 31, 2020	Jul. 31, 2019
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total accounts receivable	$ 149,085,000	$ 146,899,000
Less allowance for doubtful accounts	1,102,000	1,867,000
Accounts receivable, net	$ 147,983,000	$ 145,032,000
Accounts Receivable | Customer concentration risk | U.S. government
Accounts, Notes, Loans and Financing Receivable [Line Items]
Concentration risk, percentage	32.30%	27.80%
Billed Receivables | Commercial and International
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total accounts receivable	$ 77,080,000	$ 85,556,000
Billed Receivables | U.S. government
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total accounts receivable	$ 45,008,000	38,856,000
Unbilled Receivables
Accounts, Notes, Loans and Financing Receivable [Line Items]
Maximum period that management estimates unbilled accounts receivable to be billed and collected	1 year
Unbilled Receivables | Commercial and International
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total accounts receivable	$ 23,795,000	20,469,000
Unbilled Receivables | U.S. government
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total accounts receivable	$ 3,202,000	$ 2,018,000