Accounts Receivable (Details)	Apr. 30, 2017 USD ($)	Jul. 31, 2016 USD ($) customer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total accounts receivable	$ 121,923,000	$ 151,996,000
Less allowance for doubtful accounts	1,475,000	1,029,000
Accounts receivable, net	$ 120,448,000	$ 150,967,000
Accounts Receivable | Major customer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of customers accounted for greater than 10% of total accounts receivable | customer		0
Minimum percentage of total accounts receivable outstanding by one customer or individual country requiring additional and separate disclosure		10.00%
Accounts Receivable | Major customer | U.S. government and its agencies
Accounts, Notes, Loans and Financing Receivable [Line Items]
Percentage of total accounts receivable	22.80%	27.90%
Accounts Receivable | Major customer | Verizon Communications Inc.
Accounts, Notes, Loans and Financing Receivable [Line Items]
Percentage of total accounts receivable	11.30%
Accounts Receivable | Major customer | North African country end customers
Accounts, Notes, Loans and Financing Receivable [Line Items]
Percentage of total accounts receivable		10.50%
Billed Receivables | Commercial and International
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total accounts receivable	$ 69,149,000	$ 90,185,000
Billed Receivables | U.S. government and its agencies
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total accounts receivable	16,918,000	21,465,000
Unbilled Receivables
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retainage included in unbilled receivables	118,000	118,000
Unbilled Receivables | Commercial and International
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total accounts receivable	24,929,000	19,333,000
Unbilled Receivables | U.S. government and its agencies
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total accounts receivable	10,927,000	21,013,000
Unbilled Receivables | Major customer | U.S. Prime Contractor
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unbilled receivable related to our large over-the-horizon microwave system contracts	$ 3,593,000	$ 6,070,000