Balance Sheets - USD ($)	Jun. 30, 2018	Dec. 31, 2017
Current assets:
Cash and cash equivalents	$ 24,605,674	$ 20,023,337
Marketable securities	17,072,720	22,923,462
Prepaid expenses and other current assets	1,392,905	1,018,967
Total current assets	43,071,299	43,965,766
Deferred offering costs		165,930
Fixed assets, net	214,743	43,262
Total assets	43,286,042	44,174,958
Current liabilities:
Accounts payable	802,125	1,000,963
Accrued expenses	4,159,071	2,236,465
Current portion of credit facility	348,958	116,319
Total current liabilities	5,310,154	3,353,747
Credit facility, net of current portion and debt discount	995,291	1,220,192
Total liabilities	6,305,445	4,573,939
Commitments and contingencies (Note 11)
Stockholders' equity:
Preferred stock, $0.001 par value, 15,000,000 shares authorized, none issued and outstanding
Common stock, voting, $0.001 par value; 150,000,000 authorized and 20,842,198 and 19,137,639 shares issued and outstanding, respectively	20,842	19,138
Additional paid-in capital	154,051,733	139,241,635
Accumulated other comprehensive loss	(2,559)	(17,831)
Accumulated deficit	(117,089,419)	(99,641,923)
Total stockholders' equity	36,980,597	39,601,019
Total liabilities and stockholders' equity	43,286,042	44,174,958
Cash and Cash Equivalents [Member]
Current assets:
Cash and cash equivalents	7,605,674	2,023,337
Reverse Repurchase Agreements [Member]
Current assets:
Cash and cash equivalents	$ 17,000,000	$ 18,000,000