Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
CASH FLOWS FROM OPERATING ACTIVITIES:
Net loss	$ (74,754)	$ (114,646)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization expense	1,520	5,507
Stock-based compensation expense	1,929	7,844
Impairment of in-process research and development	32,900	0
Impairment of goodwill	0	18,057
Loss on loan extinguishment	1,366	0
Impairment of long-lived assets	13,141	6,926
Gain on lease termination	(752)	0
(Gain) loss on sale and disposal of property and equipment	(637)	7
Non-cash operating lease and interest cost	2,663	3,018
Benefit for deferred income taxes	(3,461)	0
Changes in operating assets and liabilities:
Accounts receivable	143	350
Prepaid expenses and other current assets	2,121	(2,529)
Other non-current assets	4,033	656
Accounts payable	(956)	(2,259)
Accrued expenses and other current liabilities	(7,829)	237
Other non-current liabilities	(170)	50
Operating lease liabilities	(2,762)	1,931
Net cash used in operating activities	(31,505)	(74,851)
CASH FLOWS PROVIDED BY (USED IN) INVESTING ACTIVITIES:
Proceeds on sale of property and equipment	1,327	0
Purchases of property and equipment	0	(2,182)
Net cash provided by (used in) investing activities	1,327	(2,182)
CASH FLOWS (USED IN) PROVIDED BY FINANCING ACTIVITIES:
Proceeds from exercise of stock options and issuance of common stock under employee stock purchase plan, net	0	289
Proceeds from borrowings under loan agreement, net	0	14,738
Repayment of loan	(15,000)	0
Payment of loan prepayment and termination fee	(1,155)	0
Principal payments on finance lease obligation	0	(22)
Payment of deferred offering costs	0	(132)
Net cash (used in) provided by financing activities	(16,155)	14,873
NET CHANGE IN CASH, CASH EQUIVALENTS AND RESTRICTED CASH	(46,333)	(62,160)
Cash, cash equivalents and restricted cash at beginning of year	73,805	135,965
Cash, cash equivalents and restricted cash at end of year	27,472	73,805
SUPPLEMENTAL DISCLOSURE OF CASH FLOW INFORMATION:
Cash paid for interest	202	741
Cash paid in connection with operating lease liabilities	0	(268)
SUPPLEMENTAL DISCLOSURE OF NON-CASH INVESTING AND FINANCING ACTIVITIES:
Property and equipment in accounts payable and accrued liabilities	0	14
Remeasurement of right-of-use asset	40	382
Right-of-use assets obtained in exchange for new operating lease liabilities	0	37,094
Prepaid rent reclassified to right-of-use assets	0	7,736
Prepaid rent reclassified to operating lease liability	525	0
Right-of-use assets and operating lease liability reduced for lease termination	$ 3,561	$ 0