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Debt Securities (Details) - USD ($)
3 Months Ended
Oct. 31, 2020
Oct. 31, 2019
Investments, Debt and Equity Securities [Abstract]    
Proceeds from maturities and sales of available-for-sale securities $ 6,600,000 $ 800,000
Realized gains from sales of available-for-sale securities $ 0 $ 0