Statements of Operations and Comprehensive Loss - USD ($)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Operating expenses:
Research and development expenses	$ 24,825,379	$ 17,839,951	$ 8,473,522
General and administrative expenses	14,686,767	8,658,867	4,720,661
Total operating expenses	39,512,146	26,498,818	13,194,183
Loss from operations	(39,512,146)	(26,498,818)	(13,194,183)
Other income (expense):
Warrant remeasurement	0	(1,879,823)	582,360
Other expense	(163,463)	0	0
Interest income	212,299	9,084	2,941
Interest expense	(1,203,674)	(816,494)	(183,179)
Loss before income taxes	(40,666,984)	(29,186,051)	(12,792,061)
Benefit for income taxes	1,845,986	1,107,405	590,675
Net loss	(38,820,998)	(28,078,646)	(12,201,386)
Comprehensive loss	(38,820,998)	(28,078,646)	(12,201,386)
Cumulative dividend on Series C , C-1 and C-2 convertible preferred stock	0	(4,356,408)	(1,580,701)
Net loss attributable to common stockholders	$ (38,820,998)	$ (32,435,054)	$ (13,782,087)
Loss per share attributable to common stockholders basic and diluted (in dollars per share)	$ (1.34)	$ (4.01)	$ (8.16)
Weighted average common shares outstanding basic and diluted (in shares)	28,864,216	8,087,924	1,688,475