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Marketable Investment Securities - Maturities of debt securities (Details) - USD ($)
Sep. 30, 2019
Dec. 31, 2018
Amortized Cost    
Due within one year $ 4,880,615  
Amortized Cost, Total 4,880,615 $ 7,174,000
Aggregate fair value    
Due within one year 4,880,876  
Aggregate fair value, Total $ 4,880,876 $ 7,173,037