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Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($)
 3 Months Ended
Mar. 31, 2020
Mar. 31, 2019
Cash flows from operating activities:    
Net loss $ (12,151,165) $ (15,827,200)
Adjustments to reconcile net loss to net cash used in operating activities:    
Depreciation and amortization 4,367 4,367
Accretion of marketable securities premium (64,959) (242,708)
Amortization of right-of-use assets 38,449 34,622
Stock-based compensation expense 2,198,187 2,461,699
Changes in operating assets and liabilities    
Prepaid expenses and other current assets 330,619 851,715
Accounts payable 686,050 1,225,897
Accrued expenses and other current liabilities (202,930) 1,911,423
Operating lease liabilities, current 5,864 20,609
Operating lease liabilities, noncurrent (46,879) (41,016)
Net cash used in operating activities (9,202,397) (9,600,592)
Cash flows from investing activities:    
Proceeds from the maturity and redemption of marketable securities 20,900,000 9,000,000
Purchase of marketable securities (3,871,706) (19,551,411)
Net cash provided (used in) by investing activities 17,028,294 (10,551,411)
Cash flows from financing activities:    
Proceeds from exercise of stock options 797,629 525,000
Net cash provided by financing activities 797,629 525,000
Net increase (decrease) in cash, cash equivalents and restricted cash 8,623,526 (19,627,003)
Cash, cash equivalents and restricted cash    
Beginning of period 21,512,623 50,334,871
End of period 30,136,149 30,707,868
Reconciliation of the Condensed Consolidated Statements of Cash Flows to the Condensed Consolidated Balance Sheets    
Cash and cash equivalents 30,036,149 30,607,868
Restricted cash 100,000 100,000
Total cash, cash equivalents and restricted cash $ 30,136,149 $ 30,707,868