Condensed Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019
Cash flows from operating activities:
Net loss	$ (68,480)	$ (35,653)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	1,073	900
Stock-based compensation expense	3,499	810
Change in fair value of redeemable convertible preferred stock warrant	179	(12)
Change in fair value of redeemable convertible preferred stock tranche liabilities		(2,520)
Loss on disposal of assets	32	1
Asset impairment charges	267
Changes in operating assets and liabilities:
Prepaid expenses and other current assets	(1,040)	(1,071)
Other assets	33	10
Accounts payable	7,330	(1,190)
Accrued compensation	1,076	(283)
Accrued manufacturing expenses	18,763	4,585
Accrued expenses	1,416	1,605
Deferred rent and other long-term liabilities	(8)	79
Net cash used in operating activities	(35,860)	(32,739)
Cash flows from investing activities:
Purchases of property and equipment	(433)	(242)
Proceeds from sale of property and equipment	50
Net cash used in investing activities	(383)	(242)
Cash flows from financing activities:
Payments of capital lease obligations	(61)	(220)
Proceeds from initial public offering, net of underwriters' commissions and discounts	267,375
Payment of issuance costs for initial public offering	(3,368)
Proceeds from issuance of redeemable convertible preferred stock, net of issuance costs	109,879
Proceeds from exercise of common stock options	454	315
Proceeds from issuance of common stock related to early exercised stock options	36	120
Net cash provided by (used in) financing activities	374,315	215
Net increase (decrease) in cash and cash equivalents	338,072	(32,766)
Cash and cash equivalents, beginning of period	58,976	66,090
Cash and cash equivalents, end of period	397,048	33,324
Supplemental disclosure of cash flow information:
Cash paid for interest	7	33
Supplemental disclosures of non-cash investing and financing activities:
Purchases of property and equipment recorded in accounts payable and accrued expenses	149	197
Conversion of convertible preferred stock into common stock	270,190
Issuance costs for initial public offering included in accounts payable and accrued expenses	$ 17	$ 602