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Debt Securities (Details) - USD ($)
$ in Thousands
Oct. 31, 2019
Jul. 31, 2019
Available-for-sale debt securities:    
Amortized Cost   $ 2,534
Gross Unrealized Gains  
Gross Unrealized Losses  
Fair Value $ 9,894 2,534
Certificates of deposit [Member]    
Available-for-sale debt securities:    
Amortized Cost [1] 9,894 2,234
Gross Unrealized Gains [1]
Gross Unrealized Losses [1]
Fair Value [1] $ 9,894 2,234
Municipal bonds [Member]    
Available-for-sale debt securities:    
Amortized Cost   300
Gross Unrealized Gains  
Gross Unrealized Losses  
Fair Value   $ 300
[1] Each of the Company's certificates of deposit has a CUSIP, was purchased in the secondary market through a broker, and may be sold in the secondary market.