Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Operating activities
Net loss			$ (50,012)	$ (14,786)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation expense	$ 500	$ 200	1,018	377
Stock-based compensation expense	950	462	1,771	891
In-process research and development expenses			25,591
Changes in operating assets and liabilities:
Prepaid expenses and other current assets			(828)	(30)
Other assets			(586)	38
Accounts payable			451	503
Accrued expenses and other liabilities			399	16
Deferred rent and deferred lease incentive			225	952
Net cash used in operating activities			(21,971)	(12,039)
Investing activities
Purchases of property and equipment			(531)	(4,589)
Transaction costs associated with asset acquisition			(91)
Net cash used in investing activities			(622)	(4,589)
Financing activities
Proceeds from issuance of Series A convertible preferred stock, net of issuance costs				25,322
Issuance costs associated with issuance of Series B convertible preferred stock			(34)
Payment of initial public offering costs			(739)
Principal payments on capital lease obligations			(21)	(49)
Proceeds from issuance of common stock			218	17
Net cash (used in) provided by financing activities			(576)	25,290
Net (decrease) increase in cash, cash equivalents and restricted cash			(23,169)	8,662
Cash, cash equivalents, and restricted cash, beginning of period			73,889	407
Cash, cash equivalents, and restricted cash, end of period	50,720	9,069	50,720	9,069
Supplemental cash flow information
Cash paid for interest			4	5
Non-cash investing and financing activities:
Acquisition of in process research and development through issuance of stock			25,500
Property and equipment purchases unpaid at end of period			120	3,626
Deferred offering costs unpaid at end of period			1,325
Cash and cash equivalents	49,628	7,977	49,628	7,977
Restricted cash	$ 1,092	$ 1,092	$ 1,092	$ 1,092