Accounts Receivable (Details) - USD ($)	Jul. 31, 2019	Jul. 31, 2018
Statement [Line Items]
Total accounts receivable	$ 146,899,000	$ 149,200,000
Less: Allowance for doubtful accounts	1,867,000	1,761,000
Accounts receivable, net	$ 145,032,000	$ 147,439,000
Accounts Receivable | Customer Concentration Risk | U.S. government
Statement [Line Items]
Concentration risk, percentage	27.80%	30.90%
Accounts Receivable | Customer Concentration Risk | Verizon Communications Inc.
Statement [Line Items]
Concentration risk, percentage		10.10%
Billed Receivables | Commercial and International Customers
Statement [Line Items]
Total accounts receivable	$ 85,556,000	$ 83,411,000
Billed Receivables | U.S. Government and Its Agencies
Statement [Line Items]
Total accounts receivable	38,856,000	26,251,000
Unbilled Receivables | Commercial and International Customers
Statement [Line Items]
Total accounts receivable	20,469,000	19,731,000
Unbilled Receivables | U.S. Government and Its Agencies
Statement [Line Items]
Total accounts receivable	$ 2,018,000	$ 19,807,000