Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Cash flows from operating activities:
Net loss	$ (101,167)	$ (93,867)	$ (88,696)
Adjustments to reconcile net loss to net cash used in operating activities:
Stock-based compensation expense	8,687	5,199	6,180
Depreciation and amortization expense	419	513	499
Goodwill impairment	0	0	9,758
Non-cash lease expense	1,577	1,481	1,393
Accretion of debt discount	929	918	756
Change in fair value of warrant and derivative liability	(7,074)	2,881	366
Other	(227)	37	337
Changes in operating assets and liabilities:
Prepaid expenses, other current assets and research and development incentive receivable	(1,370)	(610)	(1,755)
Accounts payable	1,234	3,425	1,166
Accrued expenses and other long-term liabilities	1,608	3,803	(152)
Operating lease liabilities	(1,128)	(882)	(698)
Operating lease right-of-use asset, net of non-cash portion	0	0	(59)
Net cash used in operating activities	(96,512)	(77,102)	(70,905)
Cash flows from investing activities:
Purchase of property, equipment and intangible assets	(60)	(103)	(615)
Purchase of marketable securities	(16,823)	0	0
Sales and maturities of marketable securities	2,000	0	0
Net cash used in investing activities	(14,883)	(103)	(615)
Cash flows from financing activities:
Proceeds from exercise of stock options, warrants and pre-funded warrants and issuance of shares of common stock under employee stock purchase plans	8,712	208	260
Issuance costs for amendments to loan and security agreement and for the sale of warrants accounted for as a liability (Note 10)	(631)	(4,802)	0
Employee taxes paid related to net share settlement of vested restricted stock units	0	(12)	0
Proceeds from borrowings under loan and security agreements	22,500	0	0
Repayments of borrowings under loan and security agreement	(2,064)	(795)	0
Proceeds from sale of shares of common stock, redeemable common stock, warrants and pre-funded warrants, net of issuance costs	59,999	122,631	75,985
Payments for Repurchase of Common Stock	0	0	(2,000)
Net cash provided by financing activities	88,516	117,230	74,245
Effect of exchange rate changes on cash, cash equivalents and restricted cash	99	(105)	(319)
Net (decrease) increase in cash, cash equivalents and restricted cash	(22,780)	39,920	2,406
Cash, cash equivalents and restricted cash at beginning of period	123,028	83,108	80,702
Cash, cash equivalents and restricted cash at end of period	100,248	123,028	83,108
Supplemental disclosure of cash flow information
Cash paid for interest	4,604	3,006	2,906
Supplemental disclosure of non-cash investing and financing activities:
Lease Obligation Incurred	0	0	1,343
Issuance costs not yet paid	$ 0	$ 661	$ 24