CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020
Cash flows from operating activities:
Net loss	$ (58,489)	$ (43,731)
Adjustments to reconcile net loss to net cash used in operating activities:
Stock-based compensation expense	4,571	4,030
Depreciation and amortization expense	367	248
Non-cash lease expense	1,031	588
Accretion of debt discount	557	389
Loss on extinguishment of debt	0	162
Other	283	(219)
Changes in operating assets and liabilities:
Prepaid expenses, other current assets and research and development incentive receivable	(14)	(2,420)
Accounts payable	(695)	121
Accrued expenses	1,069	1,722
Lease liabilities	(473)	(904)
Operating lease right-of-use asset, net of non-cash portion	59	1,300
Net cash used in operating activities	(51,852)	(41,314)
Cash flows from investing activities:
Acquisition of property, equipment and intangible assets	(602)	(1,060)
Net cash used in investing activities	(602)	(1,060)
Cash flows from financing activities:
Proceeds from exercise of stock options and pre-funded warrants and issuance of shares of common stock under employee stock purchase plan	157	468
Employee taxes paid related to net share settlement of vested restricted stock units	0	(278)
Proceeds from borrowings under loan and security agreements, net of issuance costs	0	4,888
Proceeds from sale of shares of common stock, redeemable common stock and pre-funded warrants, net of issuance costs	51,518	(313)
Settlement and retirement of redeemable common stock	(2,000)	0
Net cash provided by financing activities	49,675	4,765
Effect of exchange rate changes on cash, cash equivalents and restricted cash	(203)	240
Net decrease in cash, cash equivalents and restricted cash	(2,982)	(37,369)
Cash, cash equivalents and restricted cash at beginning of period	80,702	128,086
Cash, cash equivalents and restricted cash at end of period	77,720	90,717
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	0	2,052
Acquisition of right-of-use asset financed by lease liabilities	1,343	4,646
Issuance costs not yet paid related to sale of shares of common stock, redeemable common stock and pre-funded warrants	$ 0	$ 178