CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE LOSS - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Revenue:
Collaboration revenue	$ 32,500	$ 32,500	$ 57,500	$ 57,500
Total revenue	32,500	32,500	57,500	57,500
Operating expenses:
Research and development	5,985,230	6,581,458	19,304,124	19,922,716
General and administrative	2,987,168	3,776,575	14,201,399	12,207,080
Total operating expenses	8,972,398	10,358,033	33,505,523	32,129,796
Loss from operations	(8,939,898)	(10,325,533)	(33,448,023)	(32,072,296)
Other income (expense), net:
Interest income, net	232,240	152,763	629,289	489,728
Other income (expense), net	262	171,062	(4,062)	106,913
Net loss	$ (8,707,396)	$ (10,001,708)	$ (32,822,796)	$ (31,475,655)
Net loss per share -basic and diluted (in dollars per share)	$ (0.21)	$ (0.24)	$ (0.78)	$ (0.75)
Items included in other comprehensive income (loss):
Unrealized gain (loss) on foreign currency translation		$ 123		$ (1,158)
Unrealized gain (loss) and amounts reclassified to net loss on available-for-sale securities	$ (64,606)	51,419	$ 111,039	168,487
Other comprehensive income (loss)	(64,606)	51,542	111,039	167,329
Comprehensive loss	$ (8,772,002)	$ (9,950,166)	$ (32,711,757)	$ (31,308,326)
Weighted-average number of common shares used in net loss per share calculation - basic and diluted (in shares)	42,263,311	41,974,518	42,184,182	41,924,252