CONDENSED STATEMENTS OF CASH FLOWS (Unaudited) - USD ($)	6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015
Cash flows from operating activities:
Net loss	$ (30,923,335)	$ (29,211,643)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	213,964	165,830
Stock-based compensation expense	4,364,886	3,662,708
Fair value adjustment on warrant liability	(693,457)	(564,570)
Non-cash litigation settlement due in common stock	700,000	0
Amortization of loan cost and discount	208,148	0
Loss on retirement of fixed assets	3,388	0
Changes in assets and liabilities:
Receivables	4,368,773	(3,155,714)
Interest receivable	28,130	90,431
Prepaid expenses and other current assets	1,432,127	2,027,993
Accounts payable	(844,373)	(1,332,633)
Accrued expenses and other current liabilities	(4,297,864)	4,382,343
Net cash used in operating activities	(25,439,613)	(23,935,255)
Cash flows from investing activities:
Purchase of short-term investments	0	(17,960,256)
Proceeds from the sale of short-term investments	35,035,420	48,579,636
Purchases of equipment and furnishings	(660,758)	(69,294)
Net cash provided by investing activities	34,374,662	30,550,086
Cash flows from financing activities:
Proceeds from term loan, net	24,012,078	0
Net proceeds from exercise of warrants and stock options	704,700	0
Net cash provided by financing activities	24,716,778	0
Net increase in cash and cash equivalents	33,651,827	6,614,831
Cash and cash equivalents at beginning of period	22,261,372	32,218,905
Cash and cash equivalents at end of period	55,913,199	38,833,736
Supplemental disclosure of cash flow information:
Cash paid during the year for interest	752,083	0
Cashless warrant exercises	0	3
Cash paid for income taxes	800	800
Supplemental disclosure of non-cash investing activities:
Warrants issued in connection with term loan	633,749	0
Equipment and furnishings purchased on credit	79,247	5,022
Shares issued in connection with the class action settlement	$ 4,500,000	$ 0