Accounts Receivable (Details) - USD ($)	Oct. 31, 2019	Jul. 31, 2019
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total accounts receivable	$ 162,509,000	$ 146,899,000
Less allowance for doubtful accounts	1,465,000	1,867,000
Accounts receivable, net	$ 161,044,000	$ 145,032,000
Accounts Receivable | Major customer | U.S. government
Accounts, Notes, Loans and Financing Receivable [Line Items]
Percentage of total accounts receivable	35.40%	27.80%
Billed Receivables | Commercial and International
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total accounts receivable	$ 82,140,000	$ 85,556,000
Billed Receivables | U.S. government
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total accounts receivable	$ 55,590,000	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	$ 22,824,000	20,469,000
Unbilled Receivables | U.S. government
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total accounts receivable	$ 1,955,000	$ 2,018,000