Statements of Cash Flows - USD ($)	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017
CASH FLOWS FROM OPERATING ACTIVITIES:
Net loss	$ (17,447,496)	$ (10,399,881)
Adjustments to reconcile net loss to net cash used in operating activities:
Stock-based compensation	1,853,199	1,463,330
Amortization of debt discount - non-cash interest expense	7,738	10,392
Net amortization of premium on debt securities available for sale	7,163	130,362
Depreciation	29,282	19,963
Change in assets and liabilities:
Prepaid expenses and other current assets	(373,938)	(302,801)
Accounts payable	(198,838)	487,240
Accrued expenses	1,922,606	(907,346)
Net cash used in operating activities	(14,200,284)	(9,498,741)
CASH FLOWS FROM INVESTING ACTIVITIES:
Acquisitions of property and equipment	(200,763)	(11,592)
Purchases of marketable securities	(12,091,149)	(9,270,343)
Sales of marketable securities	17,950,000	10,822,000
Net cash provided by investing activities	5,658,088	1,540,065
CASH FLOWS FROM FINANCING ACTIVITIES:
Proceeds from issuance of common stock, net of issuance costs	13,124,533	10,585,744
Proceeds from issuance of common stock in Employee Stock Purchase Plan		45,555
Deferred offering costs paid in cash		(77,942)
Net cash provided by financing activities	13,124,533	10,553,357
NET CHANGE IN CASH AND CASH EQUIVALENTS	4,582,337	2,594,681
CASH AND CASH EQUIVALENTS, BEGINNING OF PERIOD	20,023,337	12,015,061
CASH AND CASH EQUIVALENTS, END OF PERIOD	24,605,674	14,609,742
Cash paid during the period for:
Interest	$ 46,877	$ 41,642