Condensed Consolidated Statements of Operations - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Income Statement [Abstract]
License revenue	$ 38,095	$ 38,095	$ 76,190	$ 76,190
Research and development:
Noncash compensation	567,157	1,359,446	954,082	2,697,354
Other research and development	12,966,574	9,902,214	24,196,989	18,181,645
Total research and development	13,533,731	11,261,660	25,151,071	20,878,999
General and administrative:
Noncash compensation	1,081,240	4,883,540	2,393,280	8,902,660
Other general and administrative	1,446,567	1,004,475	2,547,438	2,008,962
Total general and administrative	2,527,807	5,888,015	4,940,718	10,911,622
Total costs and expenses	16,061,538	17,149,675	30,091,789	31,790,621
Operating loss	(16,023,443)	(17,111,580)	(30,015,599)	(31,714,431)
Other (income) expense:
Interest income	(92,629)	(31,551)	(177,491)	(53,683)
Interest expense	220,756	246,526	463,161	484,183
Change in fair value of notes payable	(252,508)	(223,372)	(553,545)	(464,013)
Total other income	(124,381)	(8,397)	(267,875)	(33,513)
Net loss	$ (15,899,062)	$ (17,103,183)	$ (29,747,724)	$ (31,680,918)
Basic and diluted net loss per common share	$ (0.33)	$ (0.38)	$ (0.61)	$ (0.73)
Weighted average shares used in computing basic and diluted net loss per common share	48,769,948	45,320,637	48,838,731	43,216,385