Unaudited Statements of Cash Flows - USD ($)	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Operating activities
Net loss	$ (7,662,604)	$ (14,083,897)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation	68,191	70,441
Non-cash lease expense	164,262	149,686
Stock-based compensation expense	1,822,148	1,382,443
Changes in assets and liabilities:
Prepaid expenses and other current assets	2,267,641	(561,897)
Accounts payable	1,698,622	(832,560)
Accrued expenses	(2,059,678)	(300,817)
Noncurrent accrued expenses	393,273
Operating lease liabilities	(191,994)	(171,084)
Net cash used in operating activities	(3,500,139)	(14,347,685)
Investing activities
Purchases of property and equipment	(8,136)	(39,538)
Net cash used in investing activities	(8,136)	(39,538)
Financing activities
Proceeds from exercise of stock options	129,972	30,554
Net cash provided by financing activities	129,972	30,554
Net change in cash and cash equivalents	(3,378,303)	(14,356,669)
Cash and cash equivalents, beginning of period	158,201,441	209,917,595
Cash and cash equivalents, end of period	$ 154,823,138	195,560,926
Non-cash investing and financing activities
Property acquisition costs included in accrued expenses		$ 35,918