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Accounts Receivable (Details) - USD ($)
6 Months Ended 12 Months Ended
Jan. 31, 2022
Jul. 31, 2021
Statement [Line Items]    
Total accounts receivable $ 140,402,000 $ 159,758,000
Less allowance for doubtful accounts 1,635,000 1,648,000
Accounts receivable, net $ 138,767,000 $ 158,110,000
Accounts Receivable | Customer Concentration Risk | U.S. government    
Statement [Line Items]    
Concentration risk, percentage 21.70% 23.00%
Accounts Receivable | Customer Concentration Risk | AT&T, Inc.    
Statement [Line Items]    
Concentration risk, percentage 15.20% 12.70%
Accounts Receivable | Customer Concentration Risk | Verizon    
Statement [Line Items]    
Concentration risk, percentage 14.70% 12.10%
Billed Receivables | Commercial and International Customers    
Statement [Line Items]    
Total accounts receivable $ 75,095,000 $ 86,890,000
Billed Receivables | U.S. Government and Its Agencies    
Statement [Line Items]    
Total accounts receivable 29,079,000 33,381,000
Unbilled Receivables | Commercial and International Customers    
Statement [Line Items]    
Total accounts receivable 34,803,000 36,131,000
Unbilled Receivables | U.S. Government and Its Agencies    
Statement [Line Items]    
Total accounts receivable $ 1,425,000 $ 3,356,000