CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019
Cash flows from operating activities:
Net loss	$ (43,731)	$ (41,970)
Adjustments to reconcile net loss to net cash used in operating activities:
Stock-based compensation expense	4,030	1,386
Depreciation and amortization expense	248	71
Loss on transfer of non-financial assets	0	4,004
Non-cash lease expense	588	416
Accretion of debt discount	389	584
Loss on extinguishment of debt	162	566
Change in fair value of preferred stock warrant liability	0	288
Change in fair value of derivative liability	0	(183)
Other	(219)	0
Changes in operating assets and liabilities:
Prepaid expenses, other current assets and research and development incentive receivable	(2,420)	290
Accounts payable	121	(3,131)
Accrued expenses	1,722	(595)
Lease liabilities	(904)	(540)
Operating lease right-of-use asset, net of non-cash portion	1,300	0
Net cash used in operating activities	(41,314)	(38,814)
Cash flows from investing activities:
Cash, cash equivalents and restricted cash acquired in connection with the Merger	0	26,406
Proceeds from transfer of non-financial assets	0	896
Acquisition of property, equipment and intangible assets	(1,060)	(91)
Net cash (used in) provided by investing activities	(1,060)	27,211
Cash flows from financing activities:
Proceeds from exercise of stock options and warrants	468	605
Employee taxes paid related to net share settlement of vested restricted stock units	(278)	0
Proceeds from borrowings under loan and security agreements, net of issuance costs	4,888	9,849
Proceeds from sale of common stock and warrants, net of issuance costs	(313)	79,291
Repayments of borrowings under loan and security agreement	0	(9,368)
Net cash provided by financing activities	4,765	80,377
Effect of exchange rate changes on cash, cash equivalents and restricted cash	240	(266)
Net (decrease) increase in cash, cash equivalents and restricted cash	(37,369)	68,508
Cash, cash equivalents and restricted cash at beginning of period	128,086	8,498
Cash, cash equivalents and restricted cash at end of period	90,717	77,006
Supplemental disclosure of non-cash investing and financing activities:
Acquisition of property, equipment and right-of-use assets included in accounts payable and accrued expenses	2,052	38
Acquisition of right-of-use asset financed by lease liabilities	4,646	0
Issuance costs not yet paid	178	0
Conversion of convertible preferred stock into common stock	0	64,675
Conversion of redeemable common stock into common stock	0	734
Conversion of convertible preferred stock warrants into common stock warrants	0	5,235
Fair value of net assets acquired in the Merger	$ 0	$ 46,358