STATEMENTS OF CASH FLOWS - USD ($)	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Cash flows from operating activities:
Net loss	$ (58,587,190)	$ (30,117,980)	$ (47,485,437)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	317,649	182,927	120,399
Loss on retirement of equipment and furnishings	2,614	1,220	2,595
(Gain) loss on warrant liability	(4,437,628)	(19,051,239)	20,210,094
Unrealized foreign exchange gain	0	(125,659)	(118,438)
Stock-based compensation expense	7,384,656	6,596,248	3,985,106
Non-cash litigation settlement due in common stock	4,500,000	0	0
Changes in assets and liabilities:
Receivable	(2,574,182)	(1,901,766)	(835)
Interest receivable	76,497	(96,163)	18,053
Prepaid expenses and other current assets	1,118,931	(2,126,771)	(1,132,428)
Accounts payable	916,919	2,779,409	789,655
Accrued expenses and other current liabilities	3,699,287	3,303,967	(139,747)
Net cash used in operating activities	(47,582,447)	(40,555,807)	(23,750,983)
Cash flows from investing activities:
Proceeds from matured short-term investments	76,544,319	38,584,980	24,000,000
Purchase of short-term investments	(65,958,146)	(57,121,593)	(27,084,980)
Purchases of equipment and furnishings	(331,328)	(956,286)	(41,809)
Net cash provided by (used in) investing activities	10,254,845	(19,492,899)	(3,126,789)
Cash flows from financing activities:
Proceeds from common stock issued in public offering, net of fees	26,780,068	80,535,401	24,094,530
Proceeds from issuance of restricted stock to employee	0	100	0
Repurchase of Company's own stock for treasury	0	(182,943)	(117,070)
Net proceeds from exercise of stock options and warrants	590,001	431,941	39,336
Net cash provided by financing activities	27,370,069	80,784,499	24,016,796
Net increase (decrease) in cash and cash equivalents	(9,957,533)	20,735,793	(2,860,976)
Cash and cash equivalents at beginning of year	32,218,905	11,483,112	14,344,088
Cash and cash equivalents at end of year	22,261,372	32,218,905	11,483,112
Supplemental disclosures of non-cash financing activities:
Cashless warrant exercises	3	133	0
Repurchase of Company's own stock for treasury	0	12,671	27,829
Equipment and furnishings purchased but not paid	485,743	23,282	3,360
Retirement of treasury stock	2,612,861	0	0
Supplemental disclosure of Cash Flow Information:
Cash paid during the year for income taxes	$ 800	$ 800	$ 800