Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Cash flows from operating activities:
Net loss	$ (62,131)	$ (52,807)	$ (33,285)
Adjustments to reconcile net loss to net cash used in operating activities:
Stock-based compensation expense	5,428	2,050	759
Depreciation and amortization expense	351	103	103
Loss on transfer of nonfinancial assets	0	3,900	0
Non-cash lease expense	879	569	0
Accretion of debt discount	532	695	152
Loss on extinguishment of debt	162	566	229
Change in fair value of preferred stock warrant and derivative liability	437	105	3,487
Other	(413)	0	0
Changes in operating assets and liabilities:
Prepaid expenses, other current assets and research & development incentive receivable	(1,655)	109	279
Accounts payable	1,031	(2,752)	1,307
Accrued expenses	1,517	160	1,549
Lease liabilities	(1,067)	(753)	0
Operating lease right-of-use asset, net of non-cash portion	(3,889)	0	0
Net cash used in operating activities	(58,818)	(48,055)	(25,420)
Cash flows from investing activities:
Cash, cash equivalents and restricted cash acquired in connection with the Merger	0	26,406	0
Proceeds from transfer of non-financial assets	0	1,000	0
Purchase of property, equipment and intangible assets	(1,362)	(174)	0
Net cash provided by (used in) investing activities	(1,362)	27,232	0
Cash flows from financing activities:
Proceeds from exercise of stock options and warrants	561	792	7
Employee taxes paid related to net share settlement of vested restricted stock units	(278)	0	0
Proceeds from borrowings under loan and security agreements, net of issuance costs	12,388	9,849	9,908
Proceeds from issuance of Series B convertible preferred stock, net of issuance costs	0	0	4,461
Repurchase of Series Seed convertible preferred stock	0	0	(1,126)
Repayments of borrowings under loan and security agreement	0	(9,368)	(6,380)
Proceeds from sale of common stock and warrants, net of issuance costs	(277)	139,388	0
Net cash provided by financing activities	12,394	140,661	6,870
Effect of exchange rate changes on cash, cash equivalents and restricted cash	402	(250)	0
Net (decrease) increase in cash, cash equivalents and restricted cash	(47,384)	119,588	(18,550)
Cash, cash equivalents and restricted cash at beginning of period	128,086	8,498	27,048
Cash, cash equivalents and restricted cash at end of period	80,702	128,086	8,498
Supplemental disclosure of cash flow information
Cash paid for interest	2,099	1,284	540
Supplemental disclosure of non-cash investing and financing activities:
Purchase of property, equipment and intangible assets included in accounts payable	54	40	0
Issuance costs related to sale of common stock and warrants, not yet paid	0	775	0
Conversion of convertible preferred stock into common stock	0	64,675	0
Conversion of redeemable common stock into common stock	0	734	0
Conversion of convertible preferred stock warrants into common stock warrants	0	5,235	0
Fair value of net assets acquired in the Merger in exchange for common shares, excluding cash acquired	0	19,952	0
Initial fair value of derivative liability in connection with loan and security agreement	0	0	18
Issuance of warrants in connection with Series B convertible preferred stock financing	0	0	172
Issuance of warrants in connection with loan and security agreement	$ 0	$ 0	$ 132