Condensed Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018
Cash flows from operating activities
Net Loss	$ (24,601)	$ (9,006)
Adjustments to reconcile net loss to net cash used in operating activities:
Non-cash interest expense related to convertible promissory notes		262
Non-cash rent expense	275	61
Stock based compensation	1,479	47
Depreciation and amortization	112	27
Accretion of discount on convertible promissory notes payable		694
Amortization of discount on available for sale investments	(728)	(122)
Change in fair value of derivative liability		206
Changes in operating assets and liabilities:
Prepaid expenses and other current assets	(3,281)	20
Other assets	(253)
Accounts payable	1,800	50
Accrued expenses and other current liabilities	2,870	39
Net cash used in operating activities	(22,327)	(7,722)
Cash flow from investing activities:
Purchase of investments	(98,475)	(48,103)
Proceeds from maturities of investments	63,070
Purchase of property and equipment	(46)	(212)
Net cash used in investing activities	(35,451)	(48,315)
Cash flows from financing activities:
Proceeds from issuance of convertible promissory note payable		250
Proceeds from issuance of commons stock upon exercise of stock options	69
Proceeds from Series B redeemable convertible preferred stock		75,688
Proceeds from initial public offering, net of stock offering costs	77,827
Net cash provided by financing activities	77,896	75,938
Net increase in cash, cash equivalents and restricted cash	20,118	19,901
Cash, cash equivalents and restricted cash at beginning of period	24,872	7,393
Cash, cash equivalents and restricted cash at end of period	44,990	27,294
Supplemental disclosures of non-cash information:
Right-of-use assets obtained in exchange for new operating lease liabilities	878
Right-of-use assets obtained in exchange for new finance lease liabilities	500
Series A Redeemable Convertible Preferred Stock
Supplemental disclosures of non-cash information:
Conversion of redeemable convertible preferred stock to common stock on initial public offering	17,178
Series B Redeemable Convertible Preferred Stock
Supplemental disclosures of non-cash information:
Conversion of redeemable convertible preferred stock to common stock on initial public offering	87,816
Acceleration of vesting of stock on initial public offering	$ 856
Issuance of stock in connection with conversion of convertible promissory notes and accrued interest		11,027
Issuance of stock for facility lease		$ 1,100