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Marketable Securities (Summary of available-for-sale securities ) (Details) - USD ($)
3 Months Ended 9 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2020
Dec. 31, 2019
EMC [Member]        
Debt Securities, Available-for-sale [Line Items]        
Investment Income, Net $ 173,000 $ 223,000 $ 560,000 $ 515,000