Schedule of Available-for-sale Securities, Unrealized Loss Position (Details) - USD ($) $ in Thousands	Apr. 30, 2021	Jul. 31, 2020
DebtSecuritiesDetailsScheduleOfAvailableForSaleSecuritiesUnrealizedLossPositionLineItemsLineItems [Line Items]
Unrealized Losses	$ 142
Fair Value	12,578
US Treasury Bill Securities [Member]
DebtSecuritiesDetailsScheduleOfAvailableForSaleSecuritiesUnrealizedLossPositionLineItemsLineItems [Line Items]
Unrealized Losses	28
Fair Value	1,644
Corporate Bond Securities [Member]
DebtSecuritiesDetailsScheduleOfAvailableForSaleSecuritiesUnrealizedLossPositionLineItemsLineItems [Line Items]
Unrealized Losses	112
Fair Value	5,535
Municipal Bonds [Member]
DebtSecuritiesDetailsScheduleOfAvailableForSaleSecuritiesUnrealizedLossPositionLineItemsLineItems [Line Items]
Unrealized Losses	2	$ 16
Fair Value	$ 5,399	$ 1,963