Unaudited Condensed Statements of Cash Flows - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Cash flows from operating activities:
Net loss	$ (1,864)	$ (10,296)
Adjustments to reconcile net loss to net cash used in operating activities:
Loss on extinguishment of debt	0	16,885
Stock-based compensation expense	918	675
Amortization of debt issuance costs and debt discount	(0)	150
Depreciation and amortization expense	65	64
Fair value adjustment related to derivative and warrant liability	(241)	30
Fair value adjustment related to marketable securities and long-term investments	352	0
Consulting fees paid in common stock	50	82
Change in assets and liabilities:
Accounts and other receivables	(1,792)	(8,729)
Prepaid expenses and other assets	303	273
Operating lease right-of-use assets	51	56
Accounts payable and accrued expenses	(418)	(1,820)
Operating lease liabilities	(88)	(78)
Other liabilities	(821)	122
Net cash used in operating activities	(3,485)	(2,586)
Cash flows from investing activities:
Purchases of property and equipment	(16)	0
Purchases of marketable securities and long-term investments	(3,832)	0
Net cash used in investing activities	(3,848)	0
Cash flows from financing activities:
Proceeds from Public Offering, net of discounts and commissions	0	49,285
Payment to repurchase shares as part of the Share Repurchase Program	(4,723)	0
Payment of offering costs	(68)	(1,106)
Repayment of principal on finance lease liabilities	(10)	(61)
Payment of debt issuance costs	0	(2,881)
Repayment of principal on convertible notes	0	(37,924)
Net proceeds from exercise of common stock warrants	0	25,593
Net cash (used in) provided by financing activities	(4,801)	74,290
Net (decrease) increase in cash, cash equivalents and restricted cash	(12,134)	71,704
Cash, cash equivalents and restricted cash, beginning of period	112,346	4,322
Cash, cash equivalents and restricted cash, end of period	100,212	76,026
Supplemental cash flow information:
Cash paid for interest	5	199
Amounts due for property and equipment included in accounts payable and accrued expenses	0	4
Amounts due for deferred offering costs included in accounts payable and accrued expenses	0	17
Fair value of warrants issued to underwriters in connection with Public Offering	0	3,485
Conversion of Facility Notes into Series B-2 Preferred Stock [Member]
Supplemental cash flow information:
Notes principal converted	0	31,477
Warrants Issued in Connection with January 2021 Inducement Transaction [Member]
Cash flows from financing activities:
Proceeds from Inducement Transaction, net of discounts and commissions	$ 0	$ 41,384