Condensed Consolidated Statements of Cash Flows - USD ($)	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
CASH FLOWS FROM OPERATING ACTIVITIES:
Net loss	$ (27,727,509)	$ (13,848,662)
Adjustments to reconcile net loss to net cash used in operating activities:
Noncash stock compensation expense	5,995,455	1,698,965
Depreciation	20,416	6,380
Amortization of premium on investment securities	30,528	128,329
Change in fair value of notes payable and accrued interest	105,782	(58,632)
Changes in assets and liabilities:
Increase in restricted cash	(1,005)	(1,008)
Increase in prepaid research and development and other current assets	(3,584,938)	(2,250,490)
Decrease (increase) in leasehold interest	19,587	(1,151,163)
Decrease in accrued interest receivable	61,028	21,915
Decrease in other assets	242,372	5,341
Increase (decrease) in accounts payable and accrued expenses	2,551,726	(1,575,974)
Increase in deferred rent	22,289	389,554
Decrease in deferred revenue	(38,095)	(38,096)
Net cash used in operating activities	(22,302,364)	(16,673,541)
CASH FLOWS FROM INVESTING ACTIVITIES:
Purchases of equipment	0	(282,261)
Investment in held-to-maturity securities	0	(10,641,270)
Proceeds from maturity of short-term securities	6,000,000	9,000,000
Net cash provided by (used in) investing activities	6,000,000	(1,923,531)
CASH FLOWS FROM FINANCING ACTIVITIES:
Proceeds from the exercise of warrants	2,143,084	22,163
Proceeds from sale of common stock, net	84,765,572	0
Deferred financing costs paid	0	(8,000)
Net cash provided by financing activities	86,908,656	14,163
NET INCREASE (DECREASE) IN CASH AND CASH EQUIVALENTS	70,606,292	(18,582,909)
CASH AND CASH EQUIVALENTS AT BEGINNING OF PERIOD	25,031,280	55,061,329
CASH AND CASH EQUIVALENTS AT END OF PERIOD	95,637,572	36,478,420
NONCASH TRANSACTIONS
Reclassification of deferred financing costs to additional paid-in capital	(2,645)	0
Accrued financing costs	$ 190,709	$ 0