Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Cash flows from operating activities:
Consolidated net loss	$ (33,777)	$ (16,230)	$ (23,763)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	475	569	635
Stock-based compensation	1,614	1,465	1,783
Debt discount accretion and non-cash interest expense		346	707
Amortization (accretion) of premium (discount) of available-for-sale investment securities	366	110	(284)
Amortization of right-of-use assets	829	697	731
Loss (gain) on disposal of property and equipment	6	3	(28)
Changes in operating assets and liabilities:
Other receivables	1,604	(1,939)	58
Prepaid expenses and other assets	(3,378)	(1,122)	276
Accounts payable and accrued expenses	47	1,763	162
Contract liability		(208)	208
Operating lease liability	(861)	(755)	(498)
Net cash used in operating activities	(33,075)	(15,301)	(20,013)
Cash flows from investing activities:
Purchases of property and equipment	(192)	(202)	(79)
Purchases of available-for-sale investment securities	(126,506)	(21,066)	(40,647)
Maturities of available-for-sale investment securities	35,082	28,150	45,600
Proceeds from sale of property and equipment	50	18	51
Net cash (used in) provided by investing activities	(91,566)	6,900	4,925
Cash flows from financing activities:
Proceeds from issuance of common stock through option exercises	62
Proceeds from issuance of common stock through employee stock purchase plan	11	10	13
Proceeds from issuance of common stock from at-the-market offerings, net of offering costs	14,070	6,437	4,405
Proceeds from issuance of common stock from committed purchase agreement, net of offering costs	15,236
Proceeds from issuance of common stock from underwritten follow-on offering, net of offering costs	80,646	18,779
Proceeds from issuance of common stock through registered direct offering, net of offering costs			4,918
Repayments on borrowings		(9,083)	(8,000)
Net cash provided by financing activities	110,025	16,143	1,336
Net change in cash and cash equivalents	(14,616)	7,742	(13,752)
Cash and cash equivalents at beginning of period	16,952	9,210	22,962
Cash and cash equivalents at the end of period	$ 2,336	16,952	9,210
Supplemental disclosure of cash flow information:
Interest paid		308	$ 1,122
Purchase of fixed assets included in accounts payable		$ 17