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Statements of Cash Flows - USD ($)
 12 Months Ended
Dec. 31, 2021
Dec. 31, 2020
Dec. 31, 2019
Operating activities      
Net loss $ (63,427,437) $ (51,026,903) $ (57,891,911)
Adjustments to reconcile net loss to net cash used in operating activities:      
Depreciation 264,600 270,754 279,234
Loss on disposal of assets 2,174    
Non-cash lease expense 749,039 680,845 620,068
Stock-based compensation 6,087,286 6,901,758 6,215,090
Changes in assets and liabilities:      
Prepaid expenses and other current assets 704,524 3,087,994 (2,059,260)
Accounts payable 17,676 654,279 (1,227,919)
Accrued expenses (988,842) 993,420 2,709,986
Lease liabilities (898,550) (804,078) (629,427)
Net cash used in operating activities (57,489,530) (39,241,931) (51,984,139)
Investing activities      
Purchases of property and equipment (14,943) (68,507) (144,928)
Net cash used in investing activities (14,943) (68,507) (144,928)
Financing activities      
Proceeds from issuance of common stock, net of issuance costs 10,699,317 17,824,717  
Proceeds from exercise of stock options 25,029 319,297 412,913
Net cash provided by financing activities 10,724,346 18,144,014 412,913
Net change in cash and cash equivalents (46,780,127) (21,166,424) (51,716,154)
Cash and cash equivalents, beginning of period 137,035,017 158,201,441 209,917,595
Cash and cash equivalents, end of period $ 90,254,890 $ 137,035,017 $ 158,201,441