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Debt Securities (Details) - USD ($)
$ in Thousands
Apr. 30, 2019
Jul. 31, 2018
Available-for-sale securities:    
Amortized Cost $ 301 $ 5,613
Gross Unrealized Gains  
Gross Unrealized Losses   (1)
Fair Value 301 5,612
Certificates of deposit [Member]    
Available-for-sale securities:    
Amortized Cost [1]   3,032
Gross Unrealized Gains [1]  
Gross Unrealized Losses [1]  
Fair Value [1]   3,032
U.S. Treasury notes [Member]    
Available-for-sale securities:    
Amortized Cost   1,693
Gross Unrealized Gains  
Gross Unrealized Losses   (1)
Fair Value   1,692
Municipal bonds [Member]    
Available-for-sale securities:    
Amortized Cost 301 888
Gross Unrealized Gains
Gross Unrealized Losses
Fair Value $ 301 $ 888
[1] Each of the Company's certificates of deposit had a CUSIP, was purchased in the secondary market through a broker, and may be sold in the secondary market.