CONDENSED STATEMENTS OF CASH FLOWS (Unaudited) - USD ($)	6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016
Cash flows from operating activities:
Net loss	$ (25,402,401)	$ (30,923,335)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	348,843	213,964
Stock-based compensation expense	1,731,484	4,364,886
Fair value adjustment on warrant liabilities	4,336,066	(693,457)
Non-cash litigation settlement due in common stock	0	700,000
Amortization of loan cost and discount	975,743	208,148
Loss on retirement of fixed assets	421,843	3,388
Changes in assets and liabilities:
Receivables	136,072	4,368,773
Interest receivable	0	28,130
Prepaid expenses and other current assets	1,662,994	1,432,127
Accounts payable	673,635	(844,373)
Accrued expenses and other current liabilities	(1,026,781)	(4,297,864)
Net cash used in operating activities	(16,142,502)	(25,439,613)
Cash flows from investing activities:
Proceeds from the sale of short-term investments	0	35,035,420
Purchases of equipment and furnishings	(134,598)	(660,758)
Net cash provided by (used in) investing activities	(134,598)	34,374,662
Cash flows from financing activities:
Proceeds from public offering	13,951,218	0
Proceeds from term loan, net	0	24,012,078
Payment of principal on term loan	(2,427,362)	0
Net proceeds from exercise of warrants and stock options	2,766,605	704,700
Net cash provided by financing activities	14,290,461	24,716,778
Net increase (decrease) in cash and cash equivalents	(1,986,639)	33,651,827
Cash and cash equivalents at beginning of period	56,959,485	22,261,372
Cash and cash equivalents at end of period	54,972,846	55,913,199
Supplemental disclosure of cash flow information:
Cash paid during the year for interest	1,212,219	752,083
Cash paid for income taxes	800	800
Supplemental disclosure of non-cash activities:
Warrant liability exercise	1,558,377	0
Preferred stock conversion	7,400	0
Warrants issued in connection with term loan	0	633,749
Equipment and furnishings purchased on credit	0	79,247
Shares issued in connection with the class action settlement	$ 0	$ 4,500,000