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Marketable Securities and Fair Value Measurements - Assets and Liabilities Measured at Fair Value on a Recurring Basis (Details) - USD ($)
Dec. 31, 2018
Dec. 31, 2017
Financial assets and liabilities that are measured at fair value on recurring basis    
Long-term investments $ 9,400,000  
Investments in affiliated entities    
Financial assets and liabilities that are measured at fair value on recurring basis    
Assets, fair value 9,405,913  
Fair Value, Measurements, Recurring    
Financial assets and liabilities that are measured at fair value on recurring basis    
Assets, fair value 76,591,272 $ 124,876,806
Liabilities, fair value   360,795
Fair Value, Measurements, Recurring | Quoted Prices in Active Markets (Level 1)    
Financial assets and liabilities that are measured at fair value on recurring basis    
Assets, fair value 19,052,420 21,237,962
Liabilities, fair value   0
Fair Value, Measurements, Recurring | Significant Other Unobservable Inputs (Level 2)    
Financial assets and liabilities that are measured at fair value on recurring basis    
Assets, fair value 57,538,852 103,638,844
Liabilities, fair value   0
Fair Value, Measurements, Recurring | Significant Unobservable Inputs (Level 3)    
Financial assets and liabilities that are measured at fair value on recurring basis    
Assets, fair value 0 0
Liabilities, fair value   360,795
Fair Value, Measurements, Recurring | Money market funds    
Financial assets and liabilities that are measured at fair value on recurring basis    
Assets, fair value 9,646,507 9,843,482
Fair Value, Measurements, Recurring | Money market funds | Quoted Prices in Active Markets (Level 1)    
Financial assets and liabilities that are measured at fair value on recurring basis    
Assets, fair value 9,646,507 9,843,482
Fair Value, Measurements, Recurring | Money market funds | Significant Other Unobservable Inputs (Level 2)    
Financial assets and liabilities that are measured at fair value on recurring basis    
Assets, fair value 0 0
Fair Value, Measurements, Recurring | Money market funds | Significant Unobservable Inputs (Level 3)    
Financial assets and liabilities that are measured at fair value on recurring basis    
Assets, fair value 0 0
Fair Value, Measurements, Recurring | Mutual funds    
Financial assets and liabilities that are measured at fair value on recurring basis    
Assets, fair value 57,314,871 68,565,889
Fair Value, Measurements, Recurring | Mutual funds | Quoted Prices in Active Markets (Level 1)    
Financial assets and liabilities that are measured at fair value on recurring basis    
Assets, fair value 0 0
Fair Value, Measurements, Recurring | Mutual funds | Significant Other Unobservable Inputs (Level 2)    
Financial assets and liabilities that are measured at fair value on recurring basis    
Assets, fair value 57,314,871 68,565,889
Fair Value, Measurements, Recurring | Mutual funds | Significant Unobservable Inputs (Level 3)    
Financial assets and liabilities that are measured at fair value on recurring basis    
Assets, fair value 0 0
Fair Value, Measurements, Recurring | US corporate debt securities    
Financial assets and liabilities that are measured at fair value on recurring basis    
Assets, fair value 223,981 35,072,955
Fair Value, Measurements, Recurring | US corporate debt securities | Quoted Prices in Active Markets (Level 1)    
Financial assets and liabilities that are measured at fair value on recurring basis    
Assets, fair value 0 0
Fair Value, Measurements, Recurring | US corporate debt securities | Significant Other Unobservable Inputs (Level 2)    
Financial assets and liabilities that are measured at fair value on recurring basis    
Assets, fair value 223,981 35,072,955
Fair Value, Measurements, Recurring | US corporate debt securities | Significant Unobservable Inputs (Level 3)    
Financial assets and liabilities that are measured at fair value on recurring basis    
Assets, fair value 0 0
Fair Value, Measurements, Recurring | Investments in affiliated entities    
Financial assets and liabilities that are measured at fair value on recurring basis    
Assets, fair value   11,394,480
Fair Value, Measurements, Recurring | Investments in affiliated entities | Quoted Prices in Active Markets (Level 1)    
Financial assets and liabilities that are measured at fair value on recurring basis    
Assets, fair value   11,394,480
Fair Value, Measurements, Recurring | Investments in affiliated entities | Significant Other Unobservable Inputs (Level 2)    
Financial assets and liabilities that are measured at fair value on recurring basis    
Assets, fair value 0 0
Fair Value, Measurements, Recurring | Investments in affiliated entities | Significant Unobservable Inputs (Level 3)    
Financial assets and liabilities that are measured at fair value on recurring basis    
Assets, fair value $ 0 0
Fair Value, Measurements, Recurring | Common stock warrants    
Financial assets and liabilities that are measured at fair value on recurring basis    
Liabilities, fair value   360,795
Fair Value, Measurements, Recurring | Common stock warrants | Quoted Prices in Active Markets (Level 1)    
Financial assets and liabilities that are measured at fair value on recurring basis    
Liabilities, fair value   0
Fair Value, Measurements, Recurring | Common stock warrants | Significant Other Unobservable Inputs (Level 2)    
Financial assets and liabilities that are measured at fair value on recurring basis    
Liabilities, fair value   0
Fair Value, Measurements, Recurring | Common stock warrants | Significant Unobservable Inputs (Level 3)    
Financial assets and liabilities that are measured at fair value on recurring basis    
Liabilities, fair value   $ 360,795