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Marketable Securities and Fair Value Measurements - Assets and Liabilities Measured at Fair Value (Details) - Fair Value, Measurements, Recurring - USD ($)
Sep. 30, 2018
Dec. 31, 2017
Financial assets and liabilities that are measured at fair value on recurring basis    
Assets, fair value $ 80,576,359 $ 124,876,806
Liabilities, fair value   360,795
Using Quoted Prices in Active Markets for Identical Assets (Level 1)    
Financial assets and liabilities that are measured at fair value on recurring basis    
Assets, fair value 14,479,792 21,237,962
Liabilities, fair value   0
Using Significant Other Unobservable Inputs (Level 2)    
Financial assets and liabilities that are measured at fair value on recurring basis    
Assets, fair value 66,096,567 103,638,844
Liabilities, fair value   0
Using 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
Money market funds    
Financial assets and liabilities that are measured at fair value on recurring basis    
Assets, fair value 1,780,138 9,843,482
Money market funds | Using Quoted Prices in Active Markets for Identical Assets (Level 1)    
Financial assets and liabilities that are measured at fair value on recurring basis    
Assets, fair value 1,780,138 9,843,482
Money market funds | Using Significant Other Unobservable Inputs (Level 2)    
Financial assets and liabilities that are measured at fair value on recurring basis    
Assets, fair value 0 0
Money market funds | Using Significant Unobservable Inputs (Level 3)    
Financial assets and liabilities that are measured at fair value on recurring basis    
Assets, fair value 0 0
Mutual funds    
Financial assets and liabilities that are measured at fair value on recurring basis    
Assets, fair value 64,874,989 68,565,889
Mutual funds | Using Quoted Prices in Active Markets for Identical Assets (Level 1)    
Financial assets and liabilities that are measured at fair value on recurring basis    
Assets, fair value 0 0
Mutual funds | Using Significant Other Unobservable Inputs (Level 2)    
Financial assets and liabilities that are measured at fair value on recurring basis    
Assets, fair value 64,874,989 68,565,889
Mutual funds | Using Significant Unobservable Inputs (Level 3)    
Financial assets and liabilities that are measured at fair value on recurring basis    
Assets, fair value 0 0
US corporate debt securities    
Financial assets and liabilities that are measured at fair value on recurring basis    
Assets, fair value 1,221,578 35,072,955
US corporate debt securities | Using Quoted Prices in Active Markets for Identical Assets (Level 1)    
Financial assets and liabilities that are measured at fair value on recurring basis    
Assets, fair value 0 0
US corporate debt securities | Using Significant Other Unobservable Inputs (Level 2)    
Financial assets and liabilities that are measured at fair value on recurring basis    
Assets, fair value 1,221,578 35,072,955
US corporate debt securities | Using Significant Unobservable Inputs (Level 3)    
Financial assets and liabilities that are measured at fair value on recurring basis    
Assets, fair value 0 0
Investment in affiliated entity    
Financial assets and liabilities that are measured at fair value on recurring basis    
Assets, fair value 12,699,654 11,394,480
Investment in affiliated entity | Using Quoted Prices in Active Markets for Identical Assets (Level 1)    
Financial assets and liabilities that are measured at fair value on recurring basis    
Assets, fair value 12,699,654 11,394,480
Investment in affiliated entity | Using Significant Other Unobservable Inputs (Level 2)    
Financial assets and liabilities that are measured at fair value on recurring basis    
Assets, fair value 0 0
Investment in affiliated entity | Using Significant Unobservable Inputs (Level 3)    
Financial assets and liabilities that are measured at fair value on recurring basis    
Assets, fair value $ 0 0
Common stock warrants    
Financial assets and liabilities that are measured at fair value on recurring basis    
Liabilities, fair value   360,795
Common stock warrants | Using Quoted Prices in Active Markets for Identical Assets (Level 1)    
Financial assets and liabilities that are measured at fair value on recurring basis    
Liabilities, fair value   0
Common stock warrants | Using Significant Other Unobservable Inputs (Level 2)    
Financial assets and liabilities that are measured at fair value on recurring basis    
Liabilities, fair value   0
Common stock warrants | Using Significant Unobservable Inputs (Level 3)    
Financial assets and liabilities that are measured at fair value on recurring basis    
Liabilities, fair value   $ 360,795