CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS (UNAUDITED) - USD ($)	3 Months Ended	6 Months Ended
Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Statement Of Income And Comprehensive Income [Abstract]
Collaboration revenue	$ 926,477		$ 1,749,849
Operating expenses:
Research and development	10,289,871	$ 4,056,289	18,288,266	$ 6,855,261
General and administrative	4,527,335	1,982,231	8,355,357	3,874,778
Total operating expenses	14,817,206	6,038,520	26,643,623	10,730,039
Loss from operations	(13,890,729)	(6,038,520)	(24,893,774)	(10,730,039)
Other income (expense):
Change in fair value of convertible preferred stock tranche liability				(876,000)
Interest income	996,493	35,766	1,475,976	48,492
Total other income (expense)	996,493	35,766	1,475,976	(827,508)
Net loss and net loss attributable to common stockholders-basic and diluted	$ (12,894,236)	$ (6,002,754)	$ (23,417,798)	$ (11,557,547)
Net loss per share attributable to common stockholders-basic and diluted	$ (0.35)	$ (2.61)	$ (1.19)	$ (4.89)
Weighted-average common shares outstanding-basic and diluted	36,860,619	2,296,118	19,606,543	2,365,021

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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The aggregate costs incurred (1) in a planned search or critical investigation aimed at discovery of new knowledge with the hope that such knowledge will be useful in developing a new product or service, a new process or technique, or in bringing about a significant improvement to an existing product or process; or (2) to translate research findings or other knowledge into a plan or design for a new product or process or for a significant improvement to an existing product or process whether intended for sale or the entity's use, during the reporting period charged to research and development projects, including the costs of developing computer software up to the point in time of achieving technological feasibility, and costs allocated in accounting for a business combination to in-process projects deemed to have no alternative future use.

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Average number of shares or units issued and outstanding that are used in calculating basic and diluted earnings per share (EPS).

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