Condensed Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019
Cash flows from operating activities:
Net loss	$ (47,462)	$ (24,336)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	739	596
Stock-based compensation expense	1,661	545
Change in fair value of redeemable convertible preferred stock warrant	179	(9)
Change in fair value of redeemable convertible preferred stock tranche liabilities		(1,676)
Loss on disposal of assets	16
Asset impairment charges	267
Changes in operating assets and liabilities:
Prepaid expenses and other current assets	(264)	(781)
Other assets	44	(122)
Accounts payable	(799)	(319)
Accrued compensation	318	(600)
Accrued manufacturing expenses	20,507	3,300
Accrued expenses	1,992	43
Deferred rent and other long-term liabilities	(3)	78
Net cash used in operating activities	(22,805)	(23,281)
Cash flows from investing activities:
Purchases of property and equipment	(404)	(182)
Net cash used in investing activities	(404)	(182)
Cash flows from financing activities:
Payments of capital lease obligations	(61)	(155)
Proceeds from initial public offering, net of underwriters' commissions and discounts	267,375
Payment of issuance costs for initial public offering	(3,296)
Proceeds from issuance of redeemable convertible preferred stock, net of issuance costs	109,879
Proceeds from exercise of common stock options	346	2
Proceeds from issuance of common stock related to early exercised stock options	36
Net cash provided by (used in) financing activities	374,279	(153)
Net increase (decrease) in cash and cash equivalents	351,070	(23,616)
Cash and cash equivalents, beginning of period	58,976	66,090
Cash and cash equivalents, end of period	410,046	42,474
Supplemental disclosure of cash flow information:
Cash paid for interest	7	24
Supplemental disclosures of non-cash investing and financing activities:
Purchases of property and equipment recorded in accounts payable		$ 12
Conversion of convertible preferred stock into common stock	270,190
Issuance costs for initial public offering included in accounts payable and accrued expenses	$ 1,509