Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	3 Months Ended		15 Months Ended
	Mar. 31, 2022	Mar. 31, 2021	Mar. 31, 2022
Cash flows from operating activities
Net loss	$ (16,103)	$ (14,010)
Adjustments to reconcile net loss to net cash used in operating activities
Amortization of investment premiums, net	670	1,138
Amortization of financing costs	12	21
Stock-based compensation	2,357	1,577
Amortization of right-of-use assets	77	72
Interest expense related to operating lease liability	4	5
Changes in operating assets and liabilities:
Prepaid expenses and other current assets	23	(266)
Accrued interest, net of interest received on maturity of investments	105	(166)
Accounts payable	1,707	860
Other accrued liabilities	694	(22)
Lease liability	(76)	(85)
Net cash used in operating activities	(10,530)	(10,876)
Cash flows from investing activities
Purchases of investments	(30,682)	(48,676)
Proceeds from maturities of investments	32,301	42,049
Net cash provided by (used in) investing activities	1,619	(6,627)
Cash flows from financing activities
Value of shares withheld related to employee tax withholding	(499)	(473)
Repurchase of common stock	(5,121)
Proceeds from warrant and option exercises and stock issuances under employee stock purchase plan	614	5,664
Net cash provided by (used in) financing activities	(5,006)	5,191
Net decrease in cash and cash equivalents	(13,917)	(12,312)
Cash and cash equivalents beginning of period	26,371	29,117	$ 29,117
Cash and cash equivalents end of period	12,454	16,805	$ 12,454
Supplemental disclosure of non-cash investing and financing transactions
Unpaid deferred public offering and other financing costs	50	50
Receivable from exercise of warrants		$ 173
Right-of-use asset obtained in exchange for lease obligation	$ 1,664