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SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES, Fair Value Measurements (Details) - USD ($)
Sep. 30, 2020
Dec. 31, 2019
Fair Value Measurements [Abstract]    
Held-to-maturity securities, unrecognized gain $ 0 $ 0
Held-to-maturity securities, unrecognized (loss) 0 0
Debt Securities, Held-to-maturity [Abstract]    
Held-to-maturity securities, current 83,844,739 84,239,918
Held-to-maturity securities, noncurrent 34,321,898 16,569,024
Recurring | Institutional Money Market    
Assets at fair value    
Cash equivalents 253,460 950,658
Recurring | Certificates of deposit    
Assets at fair value    
Investments 4,568,419 7,287,409
Recurring | Municipal bonds    
Assets at fair value    
Investments 15,109,023 11,341,249
Recurring | Government agency bonds    
Assets at fair value    
Investments 4,658,191 18,182,542
Recurring | US Treasury bonds    
Assets at fair value    
Investments 6,006,593  
Recurring | Corporate bonds    
Assets at fair value    
Investments 87,824,411 63,997,742
Recurring | Level 1 | Institutional Money Market    
Assets at fair value    
Cash equivalents 253,460 950,658
Recurring | Level 1 | Certificates of deposit    
Assets at fair value    
Investments 4,568,419 7,287,409
Recurring | Level 2 | Municipal bonds    
Assets at fair value    
Investments 15,109,023 11,341,249
Recurring | Level 2 | Government agency bonds    
Assets at fair value    
Investments 4,658,191 18,182,542
Recurring | Level 2 | US Treasury bonds    
Assets at fair value    
Investments 6,006,593  
Recurring | Level 2 | Corporate bonds    
Assets at fair value    
Investments 87,824,411 63,997,742
Municipal bonds    
Debt Securities, Held-to-maturity [Abstract]    
Held-to-maturity securities, current 12,596,326 11,341,249
Held-to-maturity securities, noncurrent 2,512,697  
Government agency bonds    
Debt Securities, Held-to-maturity [Abstract]    
Held-to-maturity securities, current 1,158,191 11,950,738
Held-to-maturity securities, noncurrent 3,500,000 6,231,804
US Treasury bonds    
Debt Securities, Held-to-maturity [Abstract]    
Held-to-maturity securities, current 6,006,593  
Corporate bonds    
Debt Securities, Held-to-maturity [Abstract]    
Held-to-maturity securities, current 60,012,228 57,321,784
Held-to-maturity securities, noncurrent 27,812,183 6,675,958
Certificates of deposit    
Debt Securities, Held-to-maturity [Abstract]    
Held-to-maturity securities, current 4,071,401 3,626,147
Held-to-maturity securities, noncurrent $ 497,018 $ 3,661,262