Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2023	Jun. 30, 2022
CASH FLOWS FROM OPERATING ACTIVITIES:
Net loss	$ (9,956)	$ (26,148)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation	0	577
Stock-based compensation expense	478	1,575
Amortization of premium on marketable securities	47	549
Non-cash loss on termination of lease	0	137
Gain on sale of equipment	0	(23)
Changes in operating assets and liabilities:
Prepaid expenses and other assets	(698)	(1,007)
Accounts payable	(2,475)	(8,255)
Other liabilities	(676)	(1,904)
Net cash used in operating activities	(13,280)	(34,499)
CASH FLOWS FROM INVESTING ACTIVITIES:
Purchases of property and equipment	0	(7)
Proceeds from sale of property and equipment	0	35
Purchases of available-for-sale marketable securities	0	(3,672)
Proceeds from sales and maturities of marketable securities	7,078	49,021
Net cash provided by investing activities	7,078	45,377
CASH FLOWS FROM FINANCING ACTIVITIES:
Proceeds from issuance of pre-funded warrants for the purchase of common stock, net of issuance costs	16,567	0
Repurchase and retirement of common stock, amount	(3,000)	0
Net cash provided by financing activities	13,567	0
Net change in cash and cash equivalents	7,365	10,878
Cash and cash equivalents at beginning of period	36,640	8,305
Effect of exchange rates on cash	44	58
Cash and cash equivalents at end of period	44,049	19,241
Supplemental non-cash disclosure: NONCASH INVESTING AND FINANCING ACTIVITY:
Non-cash gain on sale of fixed assets	0	14
Operating right-of-use asset obtained in exchange for operating lease liability	0	824
Derecognition of operating right-of-use asset and operating lease liability upon termination of lease	0	714
Unrealized (loss) gain on available-for-sale securities	$ 50	$ (167)