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Investments (Details) - USD ($)
9 Months Ended 12 Months Ended
Sep. 30, 2018
Dec. 31, 2017
Amortized Cost, as Adjusted $ 22,869,924 $ 28,762,231
Short Term Investments [Member]    
Amortized Cost, as Adjusted 18,949,924 21,556,857
Gross Unrealized Holding Gains 1,237 0
Gross Unrealized Holding Losses 43,298 38,880
Estimated Fair Value 18,907,863 21,517,977
Short Term Investments [Member] | Certificates of Deposit    
Amortized Cost, as Adjusted 9,902,512 14,001,237
Gross Unrealized Holding Gains 0 0
Gross Unrealized Holding Losses 5,483 20,146
Estimated Fair Value 9,897,029 13,981,091
Short Term Investments [Member] | Governmental Agency Securities    
Amortized Cost, as Adjusted 7,551,052 5,945,314
Gross Unrealized Holding Gains 0 0
Gross Unrealized Holding Losses 37,815 18,101
Estimated Fair Value 7,513,237 5,927,213
Short Term Investments [Member] | U.S. Treasury Notes    
Amortized Cost, as Adjusted 1,496,360 1,610,306
Gross Unrealized Holding Gains 1,237 0
Gross Unrealized Holding Losses 0 633
Estimated Fair Value 1,497,597 1,609,673
Long Term Investments [Member]    
Amortized Cost, as Adjusted 3,920,000 7,205,374
Gross Unrealized Holding Gains 0 0
Gross Unrealized Holding Losses 36,722 36,388
Estimated Fair Value 3,883,278 7,168,986
Long Term Investments [Member] | Certificates of Deposit    
Amortized Cost, as Adjusted 3,920,000 4,165,000
Gross Unrealized Holding Gains 0 0
Gross Unrealized Holding Losses 36,722 21,481
Estimated Fair Value $ 3,883,278 4,143,519
Long Term Investments [Member] | Governmental Agency Securities    
Amortized Cost, as Adjusted   3,040,374
Gross Unrealized Holding Gains   0
Gross Unrealized Holding Losses   14,907
Estimated Fair Value   $ 3,025,467