Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019
Cash flows from operating activities
Net loss	$ (59,262)	$ (45,347)
Adjustments to reconcile net loss to net cash used in operating activities
Net amortization of premiums and accretion of discounts on available-for-sale securities	79
Depreciation	347	201
Stock-based compensation	6,358	3,017
Changes in operating assets and liabilities
Prepaid expenses and other current assets	1,571	(6,862)
Accrued interest on investments	(13)
Other long-term assets	(2,927)
Operating lease right-of-use asset	978	1,326
Accounts payable	(2,565)	3,711
Accrued expenses and other current liabilities	3,180	3,612
Operating lease liabilities	(981)	(613)
Net cash used in operating activities	(53,235)	(40,955)
Cash flows from investing activities
Purchases of property and equipment	(544)	(2,050)
Purchases of investments	(32,678)
Net cash used in investing activities	(33,222)	(2,050)
Cash flows from financing activities
Proceeds from issuance of common stock in initial public offering		116,251
Payment of issuance costs for common stock in initial public offering		(3,037)
Proceeds from exercise of stock options	138	17
Net cash provided by financing activities	138	163,065
Net (decrease) increase in cash, cash equivalents and restricted cash	(86,319)	120,060
Cash, cash equivalents, and restricted cash at beginning of period	168,142	63,105
Cash, cash equivalents, and restricted cash at end of period	81,823	183,165
Supplemental disclosure of non-cash investing and financing activities
Conversion of preferred stock to common stock upon the initial public offering		129,543
Issuance costs associated with public offering included in accrued expenses and other current liabilities	$ 141
Right-of-use asset obtained in exchange for operating lease obligation		3,104
Series B Preferred Stock
Cash flows from financing activities
Proceeds from issuance of Series B preferred stock		50,000
Payment of issuance costs for Series B preferred stock		$ (166)