CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS (UNAUDITED) - USD ($)	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017
Cash flows from operating activities:
Net loss	$ (23,417,798)	$ (11,557,547)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation	457,799	293,667
Stock-based compensation expense	949,192	58,258
Accretion on short-term investments	110,794
Change in fair value associated with convertible preferred stock tranche liability		876,000
Changes in operating assets and liabilities:
Prepaid expenses and other current assets	(4,129,517)	(490,997)
Accounts payable	2,566,699	148,586
Accrued expenses and other liabilities	355,175	409,415
Deferred revenue	(163,475)
Deferred rent	2,479,807	142,505
Net cash used in operating activities	(20,791,324)	(10,120,113)
Cash flows from investing activities:
Purchases of short-term investments	(143,770,078)
Maturities of short-term investments	61,220,000
Purchases of property and equipment	(4,184,136)	(1,321,727)
Changes in restricted cash	(17,375)
Net cash used in investing activities	(86,751,589)	(1,321,727)
Cash flows from financing activities:
Proceeds from issuance of common stock in initial public offering, net of discounts and issuance costs	150,843,215
Proceeds from issuance of common stock from option exercises	85,301
Net cash provided by financing activities	150,928,516	20,479,488
Increase in cash and cash equivalents	43,385,603	9,037,648
Cash and cash equivalents, beginning of period	51,574,932	11,392,207
Cash and cash equivalents, end of period	94,960,535	20,429,855
Supplemental disclosures of noncash investing and financing activities:
Reclassification of liability for common stock vested	5,750	20,605
Property and equipment additions included in accounts payable	229,509	146,735
Reclassification of tranche liability upon issuance of convertible preferred stock		5,123,000
Series A Convertible Preferred Stock
Cash flows from financing activities:
Proceeds from issuance of convertible preferred stock, net of issuance costs		$ 20,479,488
Series A Convertible Preferred Stock | Initial Public Offering
Supplemental disclosures of noncash investing and financing activities:
Conversion of convertible preferred stock into common stock upon initial public offering	42,994,550
Series B Convertible Preferred Stock | Initial Public Offering
Supplemental disclosures of noncash investing and financing activities:
Conversion of convertible preferred stock into common stock upon initial public offering	$ 94,767,610