Quarterly report pursuant to Section 13 or 15(d)

Cash, Cash Equivalents and Short-Term Investments - Schedule of Cash and Cash Equivalents and Short-term Investments by Significant Investment Category (Details)

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Cash, Cash Equivalents and Short-Term Investments - Schedule of Cash and Cash Equivalents and Short-term Investments by Significant Investment Category (Details) - USD ($)
Sep. 30, 2018
Dec. 31, 2017
Sep. 30, 2017
Dec. 31, 2016
Cash And Cash Equivalents And Short Term Investments [Line Items]        
Cash $ 2,215,116 $ 3,040,696    
Short term investments Gross Unrealized Gain (Loss) (3,545) (16,907)    
Short term investments 18,765,236 21,287,064    
Cash and cash equivalents and Short term investments, Amortized Cost 31,833,437 36,330,039    
Cash and cash equivalents and Short term investments, Estimated Fair Value 31,829,892 36,313,132    
Cash and cash equivalents 13,064,656 15,026,068 $ 18,165,647 $ 45,161,403
Level 1        
Cash And Cash Equivalents And Short Term Investments [Line Items]        
Short term investments Gross Unrealized Gain (Loss) 89 (5,540)    
Cash equivalents and Short term investments, Estimated Fair Value 8,838,138 10,720,010    
Cash equivalents and Short term investments, Amortized Cost 8,838,049 10,725,550    
Level 2        
Cash And Cash Equivalents And Short Term Investments [Line Items]        
Cash equivalents 3,000,542 3,750,621    
Short term investments Gross Unrealized Gain (Loss) (3,634) (11,367)    
Short term investments 17,776,096 18,801,805    
Cash equivalents and Short term investments, Estimated Fair Value 20,776,638 22,552,426    
Cash equivalents and Short term investments, Amortized Cost 20,780,272 22,563,793    
Money Market Funds | Level 1        
Cash And Cash Equivalents And Short Term Investments [Line Items]        
Cash equivalents 7,848,998 8,234,751    
Repurchase Agreements | Level 2        
Cash And Cash Equivalents And Short Term Investments [Line Items]        
Cash equivalents 3,000,542 3,000,233    
US Treasury Securities | Level 1        
Cash And Cash Equivalents And Short Term Investments [Line Items]        
Short Term Investments Amortized Cost 989,051 2,490,799    
Short term investments Gross Unrealized Gain (Loss) 89 (5,540)    
Short term investments 989,140 2,485,259    
Commercial Paper | Level 2        
Cash And Cash Equivalents And Short Term Investments [Line Items]        
Short Term Investments Amortized Cost 8,531,479 9,716,093    
Short term investments 8,531,479 9,716,093    
Cash equivalents and Short term investments, Estimated Fair Value 8,531,479      
Corporate Debt Securities | Level 2        
Cash And Cash Equivalents And Short Term Investments [Line Items]        
Short Term Investments Amortized Cost 5,936,106 6,829,191    
Short term investments Gross Unrealized Gain (Loss) (2,008) (9,414)    
Short term investments 5,934,098 6,819,777    
Asset-backed Securities | Level 2        
Cash And Cash Equivalents And Short Term Investments [Line Items]        
Cash equivalents   750,388    
Short Term Investments Amortized Cost 3,312,145 3,018,276    
Short term investments Gross Unrealized Gain (Loss) (1,626) (1,953)    
Short term investments 3,310,519 2,265,935    
Cash equivalents and Short term investments, Estimated Fair Value $ 3,310,519 $ 3,016,323