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Accounts Receivable (Details) - USD ($)
12 Months Ended
Jul. 31, 2021
Jul. 31, 2020
Statement [Line Items]    
Total accounts receivable $ 159,758,000 $ 128,585,000
Less: Allowance for doubtful accounts 1,648,000 1,769,000
Accounts receivable, net $ 158,110,000 126,816,000
Cumulative Effect, Period of Adoption, Adjustment    
Statement [Line Items]    
Less: Allowance for doubtful accounts   $ 215,000
U.S. Government and Its Agencies | Accounts Receivable | Customer Concentration Risk    
Statement [Line Items]    
Concentration risk, percentage 23.00% 31.00%
AT&T, Inc. | Accounts Receivable | Customer Concentration Risk    
Statement [Line Items]    
Concentration risk, percentage 12.70%  
Verizon Communications Inc. | Accounts Receivable | Customer Concentration Risk    
Statement [Line Items]    
Concentration risk, percentage 12.10%  
Billed Receivables | Commercial and International Customers    
Statement [Line Items]    
Total accounts receivable $ 86,890,000 $ 67,109,000
Billed Receivables | U.S. Government and Its Agencies    
Statement [Line Items]    
Total accounts receivable 33,381,000 32,870,000
Unbilled Receivables | Commercial and International Customers    
Statement [Line Items]    
Total accounts receivable 36,131,000 21,588,000
Unbilled Receivables | U.S. Government and Its Agencies    
Statement [Line Items]    
Total accounts receivable $ 3,356,000 $ 7,018,000