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SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES, Fair Value Measurements (Details) - USD ($)
12 Months Ended
Dec. 31, 2019
Dec. 31, 2018
Fair Value Measurements [Abstract]    
Held-to-maturity securities, unrecognized gain $ 0 $ 0
Held-to-maturity securities, unrecognized (loss) 0 0
Interest income 1,986,855 1,294,651
Amortized net premium / (net discount) included in interest income 32,000 372,000
Remaining unamortized net premium / (net discount) 285,000 (121,000)
Debt Securities, Held-to-maturity [Abstract]    
Held-to-maturity securities, current 84,239,918 67,707,143
Held-to-maturity securities, noncurrent 16,569,024 1,099,834
Municipal Bonds [Member]    
Debt Securities, Held-to-maturity [Abstract]    
Held-to-maturity securities, current 11,341,249 1,295,350
Held-to-maturity securities, noncurrent 0 0
Government Agency Bonds [Member]    
Debt Securities, Held-to-maturity [Abstract]    
Held-to-maturity securities, current 11,950,738 0
Held-to-maturity securities, noncurrent 6,231,804 0
Corporate Bonds [Member]    
Debt Securities, Held-to-maturity [Abstract]    
Held-to-maturity securities, current 57,321,784 61,321,162
Held-to-maturity securities, noncurrent 6,675,958 1,099,834
Certificates of Deposit [Member]    
Debt Securities, Held-to-maturity [Abstract]    
Held-to-maturity securities, current 3,626,147 5,090,631
Held-to-maturity securities, noncurrent $ 3,661,262 $ 0