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Investments - Narrative (Details) - USD ($)
3 Months Ended 6 Months Ended
Sep. 30, 2021
Sep. 30, 2020
Sep. 30, 2021
Sep. 30, 2020
Mar. 31, 2021
Investments, Debt and Equity Securities [Abstract]          
Accrued interest $ 1,500,000   $ 1,500,000   $ 300,000
Debt securities credit losses $ 0 $ 0 $ 0 $ 0