Consolidated Statements of Operations and Comprehensive Loss - USD ($)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Operating expenses:
Research and development	$ 41,313,942	$ 32,691,445	$ 17,923,348
General and administrative	28,466,350	13,371,631	9,063,926
Total operating expenses	69,780,292	46,063,076	26,987,274
Loss from operations	(69,780,292)	(46,063,076)	(26,987,274)
Other income (expense):
Interest income	1,520,659	1,246,133	478,715
Interest expense	(1,747,186)	(570,990)	(401,370)
Other income (expense), net	(1,887,140)	(927,518)	(403,735)
Total other income (expense)	(2,113,667)	(252,375)	(326,390)
Net loss	$ (71,893,959)	$ (46,315,451)	$ (27,313,664)
Net loss per common share, basic and diluted	$ (2.84)	$ (2.15)	$ (1.97)
Weighted average common shares outstanding, basic and diluted	25,296,527	21,497,119	13,893,961
Other comprehensive gain (loss) :
Unrealized gains (losses) from available-for-sale securities, net of tax of $0	$ 26,038	$ (91,411)	$ (5,212)
Total other comprehensive income (loss)	26,038	(91,411)	(5,212)
Comprehensive loss	$ (71,867,921)	$ (46,406,862)	$ (27,318,876)