$ in Thousands
12 Months Ended
Dec. 31, 2023
Dec. 31, 2022
Operating activities    
Net loss $ (164,574) $ (94,654)
Adjustments to reconcile net loss to net cash used in operating activities:    
Depreciation and amortization 2,252 2,706
Non-cash lease expense 76 261
Impairment of long-lived assets 515  
Transaction costs allocated to warrants issued in connection with private placement   5,015
Stock-based compensation expense 10,434 11,410
Change in fair value of warrant liabilities 37,275 (43,221)
Net amortization of premiums and discounts on marketable securities (1,314) 243
Amortization of debt-discount and accretion of deferred debt costs 574 692
Changes in operating assets and liabilities:    
Prepaid expenses and other current assets 1,940 (2,807)
Unbilled receivable 1,694 1,285
Other long-term assets 3,756 (2,407)
Accounts payable 5,133 2,766
Accrued expenses (2,179) 2,345
Deferred revenue (4,330) (5,851)
Operating lease liabilities (959) (848)
Net cash used in operating activities (109,707) (123,065)
Investing activities    
Purchases of property and equipment (272) (1,241)
Proceeds from the disposition of property and equipment 1,560  
Purchases of marketable securities (50,968)  
Maturities of marketable securities 87,017 68,426
Net cash provided by (used in) investing activities 37,337 67,185
Financing activities    
Payments on financing lease obligations (65) (291)
Proceeds from the issuance of common stock through employee stock purchase plan 257 217
Proceeds from the issuance of common stock through exercise of stock options   1
Payment to creditor related to debt modification   (300)
Proceeds from issuance of common stock through at-the-market sales agreement, net of issuance costs 1,357  
Proceeds from issuance of common stock and pre-funded warrants in an underwritten registered direct offering, net of issuance costs 41,913  
Cash and cash equivalents acquired in connection with merger,net of issuance costs paid   11,762
Proceeds from issuance of common stock and accompanying warrants and pre-funded warrants in private placement, net of issuance costs   119,761
Redemption of fractional shares due to the reverse stock split   (81)
Payment of issuance costs related to out of period offering   (24)
Net cash provided by financing activities 43,462 131,045
Net (decrease) increase in cash, cash equivalents and restricted cash (28,908) 75,165
Cash, cash equivalents and restricted cash, Beginning of year 170,553 95,388
Cash, cash equivalents and restricted cash, End of year 141,645 170,553
Supplemental disclosure of cash flow information:    
Cash paid for interest 4,552 3,408
Non-cash investing and financing activities:    
Offering costs incurred but unpaid as of year end $ 138 $ 10