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Investments - Summary of Available-for-sale Securities (Details) - USD ($)
9 Months Ended 12 Months Ended
Sep. 30, 2018
Dec. 31, 2017
Jun. 30, 2015
Debt Securities, Available-for-sale [Abstract]      
Cost $ 66,378,328    
Gross Unrealized Gains 680    
Gross Unrealized Losses (282,441)    
Fair Market Value 66,096,567    
Cost   $ 0 $ 0
Gross Unrealized Gains   2,325,079  
Gross Unrealized Losses   0  
Fair Market Value   2,325,079  
Cost   103,986,286  
Gross Unrealized Gains   2,370,208  
Gross Unrealized Losses   (392,571)  
Fair Market Value   105,963,923  
Mutual funds      
Debt Securities, Available-for-sale [Abstract]      
Cost 65,154,422 68,776,165  
Gross Unrealized Gains 680 42,097  
Gross Unrealized Losses (280,113) (252,373)  
Fair Market Value 64,874,989 68,565,889  
US corporate debt securities      
Debt Securities, Available-for-sale [Abstract]      
Cost 1,223,906 35,210,121  
Gross Unrealized Gains 0 3,032  
Gross Unrealized Losses (2,328) (140,198)  
Fair Market Value $ 1,221,578 $ 35,072,955  
Maximum | US corporate debt securities      
Debt Securities, Available-for-sale [Line Items]      
Contractual maturity, less than 2 years 2 years