STATEMENTS OF CASH FLOWS - USD ($)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Cash flows from operating activities:
Net loss	$ (50,771,221)	$ (58,587,190)	$ (30,117,980)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	536,631	317,649	182,927
Loss on retirement of equipment and furnishings	12,276	2,614	1,220
Gain on warrant liabilities	(3,827,617)	(4,437,628)	(19,051,239)
Amortization of loan cost and discount	587,837	0	0
Unrealized foreign exchange gain	0	0	(125,659)
Stock-based compensation expense	6,735,576	7,384,656	6,596,248
Non-cash litigation settlement due in common stock	0	4,500,000	0
Changes in assets and liabilities:
Receivable	4,412,097	(2,574,182)	(1,901,766)
Interest receivable	28,130	76,497	(96,163)
Prepaid expenses and other assets	(28,569)	1,118,931	(2,126,771)
Accounts payable	(1,672,631)	916,919	2,779,409
Accrued expenses and other current liabilities	(5,862,861)	3,699,287	3,303,967
Net cash used in operating activities	(49,850,352)	(47,582,447)	(40,555,807)
Cash flows from investing activities:
Proceeds from matured short-term investments	35,035,420	76,544,319	38,584,980
Purchase of short-term investments	0	(65,958,146)	(57,121,593)
Purchases of equipment and furnishings	(1,020,441)	(331,328)	(956,286)
Net cash provided by (used in) investing activities	34,014,979	10,254,845	(19,492,899)
Cash flows from financing activities:
Proceeds from common stock issued in public offering, net of fees	25,777,257	26,780,068	80,535,401
Proceeds from term loan, net	24,012,078	0	0
Proceeds from issuance of restricted stock to employee	0	0	100
Repurchase of Company's own stock for treasury	0	0	(182,943)
Net proceeds from exercise of stock options and warrants	744,151	590,001	431,941
Net cash provided by financing activities	50,533,486	27,370,069	80,784,499
Net increase (decrease) in cash and cash equivalents	34,698,113	(9,957,533)	20,735,793
Cash and cash equivalents at beginning of year	22,261,372	32,218,905	11,483,112
Cash and cash equivalents at end of year	56,959,485	22,261,372	32,218,905
Supplemental disclosures of non-cash financing/investing activities:
Cashless warrant exercises	0	3	133
Repurchase of Company's own stock for treasury	0	0	12,671
Receivable from issuance of restricted stock	2,325	0	0
Equipment and furnishings purchased but not paid	20,452	485,743	232,825
Retirement of treasury stock	0	2,612,861	0
Warrants issued in connection with the term loan	633,749	0	0
Shares issued in connection with the class action settlement	4,500,000	0	0
Series B Preferred stock beneficial conversion feature and deemed dividend	314,286	0	0
Warrants issued/amended in connection with the public offering	6,923,551	0	0
Series B Preferred stock conversion	457	0	0
Supplemental disclosure of Cash Flow Information:
Cash paid during the year for income taxes	800	800	800
Cash paid during the year for interest	$ 1,959,375	$ 0	$ 0