CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS (UNAUDITED) - USD ($)	3 Months Ended	9 Months Ended
Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Statement Of Income And Comprehensive Income [Abstract]
Collaboration revenue	$ 954,149		$ 2,703,998
Operating expenses:
Research and development	13,393,759	$ 4,946,611	31,667,396	$ 11,801,872
General and administrative	3,843,343	1,718,159	12,213,329	5,592,937
Total operating expenses	17,237,102	6,664,770	43,880,725	17,394,809
Loss from operations	(16,282,953)	(6,664,770)	(41,176,727)	(17,394,809)
Other income (expense):
Change in fair value of convertible preferred stock tranche liability				(876,000)
Interest income	1,487,190	137,202	2,963,166	185,694
Total other income (expense)	1,487,190	137,202	2,963,166	(690,306)
Net loss and net loss attributable to common stockholders-basic and diluted	$ (14,795,763)	$ (6,527,568)	$ (38,213,561)	$ (18,085,115)
Net loss per share attributable to common stockholders-basic and diluted	$ (0.40)	$ (2.78)	$ (1.48)	$ (7.43)
Weighted-average common shares outstanding-basic and diluted	37,273,402	2,351,398	25,849,608	2,434,651

Increase (decrease) in fair market value of convertible preferred stock tranche liability.

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The amount of net income or loss for the period per each share in instances when basic and diluted earnings per share are the same amount and reported as a single line item on the face of the financial statements. Basic earnings per share is the amount of net income or loss for the period per each share of common stock or unit outstanding during the reporting period. Diluted earnings per share includes the amount of net income or loss for the period available to each share of common stock or common unit outstanding during the reporting period and to each share or unit that would have been outstanding assuming the issuance of common shares or units for all dilutive potential common shares or units outstanding during the reporting period.

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