Accounts Receivable (Details) - USD ($)	6 Months Ended	12 Months Ended
	Jan. 31, 2021	Jul. 31, 2020	Aug. 01, 2020
Statement [Line Items]
Total accounts receivable	$ 152,030,000	$ 128,585,000
Less allowance for doubtful accounts	2,102,000	1,769,000
Accounts receivable, net	$ 149,928,000	$ 126,816,000
Cumulative Effect, Period of Adoption, Adjustment
Statement [Line Items]
Less allowance for doubtful accounts			$ 215,000
Accounts Receivable | Customer Concentration Risk | U.S. government
Statement [Line Items]
Concentration risk, percentage	32.50%	31.00%
Accounts Receivable | Customer Concentration Risk | Verizon
Statement [Line Items]
Concentration risk, percentage	12.70%
Billed Receivables | Commercial and International Customers
Statement [Line Items]
Total accounts receivable	$ 77,551,000	$ 67,109,000
Billed Receivables | U.S. Government and Its Agencies
Statement [Line Items]
Total accounts receivable	43,241,000	32,870,000
Unbilled Receivables | Commercial and International Customers
Statement [Line Items]
Total accounts receivable	25,137,000	21,588,000
Unbilled Receivables | U.S. Government and Its Agencies
Statement [Line Items]
Total accounts receivable	$ 6,101,000	$ 7,018,000