Condensed Consolidated Statements of Operations - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Income Statement [Abstract]
License revenue	$ 38,096	$ 38,096	$ 114,286	$ 114,286
Research and development:
Noncash compensation	919,648	35,756	1,873,730	2,733,110
Other research and development	20,878,108	11,538,246	45,075,097	29,719,891
Total research and development	21,797,756	11,574,002	46,948,827	32,453,001
General and administrative:
Noncash compensation	1,914,390	1,204,278	4,307,670	10,106,938
Other general and administrative	1,251,421	1,085,400	3,798,859	3,094,362
Total general and administrative	3,165,811	2,289,678	8,106,529	13,201,300
Total costs and expenses	24,963,567	13,863,680	55,055,356	45,654,301
Operating loss	(24,925,471)	(13,825,584)	(54,941,070)	(45,540,015)
Other (income) expense:
Interest income	(87,965)	(55,977)	(265,456)	(109,660)
Other income	(33,042)	0	(33,042)	0
Interest expense	211,538	246,527	674,699	730,710
Change in fair value of notes payable	(184,975)	(360,218)	(738,520)	(824,231)
Total other income	(94,444)	(169,668)	(362,319)	(203,181)
Net loss	$ (24,831,027)	$ (13,655,916)	$ (54,578,751)	$ (45,336,834)
Basic and diluted net loss per common share	$ (0.50)	$ (0.28)	$ (1.11)	$ (1.01)
Weighted average shares used in computing basic and diluted net loss per common share	49,203,277	47,946,309	48,961,582	44,810,352