CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS (UNAUDITED) - USD ($)	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Statement Of Income And Comprehensive Income [Abstract]
Collaboration revenue	$ 823,372
Operating expenses:
Research and development	7,997,605	$ 2,799,136
General and administrative	3,828,022	1,892,382
Total operating expenses	11,825,627	4,691,518
Loss from operations	(11,002,255)	(4,691,518)
Other income:
Change in fair value of convertible preferred stock tranche liability		(876,000)
Interest income	479,483	12,725
Total other income (expense)	479,483	(863,275)
Net loss and net loss attributable to common stockholders-basic and diluted	$ (10,522,772)	$ (5,554,793)
Net loss per share attributable to common stockholders-basic and diluted	$ (4.21)	$ (2.79)
Weighted average common shares outstanding-basic and diluted	2,500,178	1,992,014