CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE LOSS - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Revenue:
Collaboration revenue	$ 12,500	$ 12,500	$ 25,000	$ 25,000
Total revenue	12,500	12,500	25,000	25,000
Operating expenses:
Research and development	6,787,341	6,723,950	13,318,894	13,341,258
General and administrative	7,394,473	4,070,589	11,214,231	8,430,505
Total operating expenses	14,181,814	10,794,539	24,533,125	21,771,763
Loss from operations	(14,169,314)	(10,782,039)	(24,508,125)	(21,746,763)
Other income (expense), net:
Interest income, net	207,514	184,494	397,049	336,965
Other expense, net	(860)	(6,573)	(4,324)	(64,149)
Net loss	$ (13,962,660)	$ (10,604,118)	$ (24,115,400)	$ (21,473,947)
Net loss per share -basic and diluted (in dollars per share)	$ (0.33)	$ (0.25)	$ (0.57)	$ (0.51)
Items included in other comprehensive income (loss):
Unrealized loss on foreign currency translation		$ (1,597)		$ (1,281)
Unrealized gain (loss) on available-for-sale securities	$ 65,509	(17,448)	$ 175,645	117,068
Other comprehensive income (loss)	65,509	(19,045)	175,645	115,787
Comprehensive loss	$ (13,897,151)	$ (10,623,163)	$ (23,939,755)	$ (21,358,160)
Weighted-average number of common shares used in net loss per share calculation - basic and diluted (in shares)	42,178,537	41,939,052	42,144,182	41,898,702