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Marketable Securities and Fair Value Measurements - Assets and Liabilities Measured at Fair Value (Details) - Fair Value, Measurements, Recurring - USD ($)
Jun. 30, 2018
Dec. 31, 2017
Financial assets and liabilities that are measured at fair value on recurring basis    
Assets, fair value $ 93,841,418 $ 124,876,806
Liabilities, fair value 228,665 360,795
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 13,332,054 21,237,962
Liabilities, fair value 0 0
Using Significant Other Unobservable Inputs (Level 2)    
Financial assets and liabilities that are measured at fair value on recurring basis    
Assets, fair value 80,509,364 103,638,844
Liabilities, fair value 0 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 228,665 360,795
Money market funds    
Financial assets and liabilities that are measured at fair value on recurring basis    
Assets, fair value 1,649,759 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 1,649,759 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 69,322,516 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 69,322,516 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 11,186,848 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 11,186,848 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 11,682,295 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 11,682,295 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 228,665 360,795
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 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 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 $ 228,665 $ 360,795