Consolidated Statements of Cash Flows - USD ($)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
CASH FLOWS FROM OPERATING ACTIVITIES
Consolidated net loss	$ (78,252,894)	$ (62,948,646)	$ (55,781,277)
Adjustments to reconcile consolidated net loss to net cash used in operating activities:
Gain on settlement of notes payable	0	0	(95,427)
Gain on sale of long-term securities	(33,042)	0	0
Noncash stock compensation expense	7,509,999	15,697,092	21,105,292
Noncash stock expense associated with in-licensing agreements	0	0	5,350,094
Depreciation	62,960	15,452	3,931
Amortization of premium on investment securities	459,429	536,142	193,581
Change in fair value of notes payable and accrued interest	(109,657)	(56,717)	210,661
Changes in assets and liabilities:
Increase in restricted cash	(4,065)	(4,131)	(575,012)
Decrease (increase) in other current assets	3,564,316	(3,105,771)	(4,563,067)
Increase in leasehold interest	(2,042,281)	0	0
(Decrease) increase in accrued interest receivable	102,169	(100,505)	(58,347)
Increase in other assets	(4,784)	(41,722)	0
Increase (decrease) in accounts payable and accrued expenses	6,492,644	5,470,915	(603,377)
Decrease in interest payable	0	0	(94,590)
Increase in deferred rent	816,257	0	0
Decrease in deferred revenue	(152,381)	(152,381)	(152,381)
Net cash used in operating activities	(61,591,330)	(44,690,272)	(35,059,919)
CASH FLOWS FROM INVESTING ACTIVITIES
Purchases of equipment	(343,985)	(42,217)	(18,570)
Investment in held-to-maturity securities	(15,199,922)	(48,993,652)	(18,336,719)
Proceeds from maturity of short-term securities	29,500,000	24,350,000	0
Proceeds from the sale of long-term securities	12,589,219	0	0
Net cash provided by (used in) investing activities	26,545,312	(24,685,869)	(18,355,289)
CASH FLOWS FROM FINANCING ACTIVITIES
Proceeds from the exercise of warrants	618,242	1,067,339	3,556,624
Proceeds from the exercise of options	0	0	202,400
Payment of notes payable	0	0	(677,778)
Proceeds from sale of common stock, net	4,411,233	67,760,517	65,614,260
Deferred financing costs paid	(13,506)	(104,170)	(51,980)
Net cash provided by financing activities	5,015,969	68,723,686	68,643,526
NET (DECREASE) INCREASE IN CASH AND CASH EQUIVALENTS	(30,030,049)	(652,455)	15,228,318
Cash and cash equivalents at beginning of year	55,061,329	55,713,784	40,485,466
CASH AND CASH EQUIVALENTS AT END OF YEAR	25,031,280	55,061,329	55,713,784
NONCASH TRANSACTIONS
Reclassification of deferred financing costs to additional paid-in capital	(25,097)	(111,810)	0
Conversion of convertible notes payable to common stock	$ 33,017	$ 6,924	$ 0