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Available-for-Sale Securities - Additional Information (Details) - USD ($)
3 Months Ended 9 Months Ended 12 Months Ended
Sep. 30, 2018
Sep. 30, 2017
Sep. 30, 2018
Sep. 30, 2017
Dec. 31, 2017
Investments Debt And Equity Securities [Abstract]          
Available for sale securities $ 27,613,031   $ 27,613,031   $ 0
Unrealized gain on short and long-term investments $ 2,457 $ 0 (8,882) $ 1,090  
Available-For-Sale Securities          
Schedule Of Available For Sale Securities [Line Items]          
Other-than-temporary impairment     $ 0   $ 0