Condensed Consolidated Statements of Cash Flows - USD ($)	9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015
CASH FLOWS FROM OPERATING ACTIVITIES:
Net loss	$ (54,578,751)	$ (45,336,834)
Adjustments to reconcile net loss to net cash used in operating activities:
Gain on sale of long-term securities	(33,042)	0
Noncash stock compensation expense	6,181,400	12,840,048
Depreciation	42,464	10,326
Amortization of premium on investment securities	367,673	377,770
Change in fair value of notes payable and accrued interest	(63,822)	(93,522)
Changes in assets and liabilities:
Increase in restricted cash	(3,041)	(3,114)
Increase in prepaid research and development and other current assets	(1,162,310)	(4,055,116)
Increase in leasehold interest	(2,517,771)	0
Decrease (increase) in accrued interest receivable	77,563	(73,011)
Increase in other assets	(3,523)	0
Increase in accounts payable and accrued expenses	6,447,215	4,658,128
Increase in deferred rent	793,968	0
Decrease in deferred revenue	(114,286)	(114,286)
Net cash used in operating activities	(44,566,263)	(31,789,611)
CASH FLOWS FROM INVESTING ACTIVITIES:
Purchases of equipment	(323,015)	(59,194)
Investment in held-to-maturity securities	(15,199,922)	(40,955,137)
Proceeds from maturity of short-term securities	18,000,000	13,850,000
Proceeds from sale of long-term securities	12,589,219	0
Net cash provided by (used in) investing activities	15,066,282	(27,164,331)
CASH FLOWS FROM FINANCING ACTIVITIES:
Proceeds from the exercise of warrants	100,896	1,009,985
Proceeds from sale of common stock, net	3,504,261	67,760,517
Financing costs	(9,984)	(68,404)
Net cash provided by financing activities	3,595,173	68,702,098
NET (DECREASE) INCREASE IN CASH AND CASH EQUIVALENTS	(25,904,808)	9,748,156
CASH AND CASH EQUIVALENTS AT BEGINNING OF PERIOD	55,061,329	55,713,784
CASH AND CASH EQUIVALENTS AT END OF PERIOD	29,156,521	65,461,940
NONCASH TRANSACTIONS
Reclassification of deferred financing costs to additional paid-in capital	(56,988)	(63,788)
Conversion of convertible notes payable to common stock	$ 30,601	$ 0