Condensed Statements of Cash Flows - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019
Cash flows from operating activities
Net loss	$ (16,149)	$ (14,090)
Adjustments to reconcile net loss to net cash used in operating activities:
Stock based compensation	201	157
Change in fair value of notes payable	83	0
Change in operating assets and liabilities:
Prepaid expenses and other current assets	(610)	(207)
Accounts payable	(31)	(192)
Accrued expenses	464	(373)
Net cash used in operating activities	(16,042)	(14,705)
Cash flows from financing activities
Cash received from stock option exercise	0	74
Cash paid for initial public offering costs	(398)	0
Proceeds from issuance of redeemable convertible preferred stock, net of issuance costs	82,544	10,949
Proceeds from issuance of convertible loan notes	10,000	0
Net cash provided by financing activities	92,146	11,023
Net increase (decrease) in cash, cash equivalents and restricted cash	76,104	(3,682)
Cash, cash equivalents and restricted cash at beginning of period	4,205	12,079
Cash, cash equivalents and restricted cash at end of period	80,309	8,397
Supplemental disclosure of non-cash financing activities:
Accretion of issuance costs to redeemable convertible preferred stock	456	51
Exercise of series B preferred stock tranche right	300	0
Accrued dividends on redeemable convertible preferred stock	3,957	2,728
Deferred offering costs included in prepaid expenses and other current assets and accounts payable or accrued expenses	1,217	0
Series C Redeemable Convertible Preferred Stock [Member]
Cash flows from financing activities
Cash paid for initial public offering costs	(429)
Supplemental disclosure of non-cash financing activities:
Conversion of convertible loan notes into series C preferred stock	$ 10,083	$ 0