Consolidated Statements of Cash Flows - USD ($)	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Cash flows from operating activities:
Net loss	$ (48,663,000)	$ (32,845,000)	$ (47,339,000)
Adjustments to reconcile net loss to net cash used in operating activities:
Stock-based compensation expense	3,671,000	4,051,000	2,989,000
Depreciation expense	363,000	166,000	163,000
Non-cash interest expense	53,000	34,000	8,000
Non-cash lease expense	372,000	601,000	486,000
Loss (gain) on sale of equipment	9,000	(7,000)
Changes in assets and liabilities:
Prepaid expenses and other current assets	(811,000)	821,000	(202,000)
Other assets			123,000
Accounts payable	(1,377,000)	(544,000)	972,000
Accrued expenses	1,005,000	75,000	(301,000)
Operating lease liabilities	(300,000)	(564,000)	(531,000)
Other liabilities		53,000
Net cash used in operating activities	(45,678,000)	(28,159,000)	(43,632,000)
Cash flows from investing activities:
Purchases of property and equipment	(667,000)	(650,000)	(122,000)
Sales of property and equipment		18,000
Net cash used in investing activities	(667,000)	(632,000)	(122,000)
Cash flows from financing activities:
Proceeds from (payments of issuance costs related to) the issuance of common stock, net of issuance costs	41,273,000	33,995,000	12,035,000
Proceeds from exercise of stock options		17,000	36,000
Proceeds from issuance of stock through ESPP	18,000	52,000	76,000
Proceeds from loan payable		10,000,000
Repayment of loan payable		(10,000,000)
Debt issuance costs paid		(214,000)
Other		(24,000)	(29,000)
Net cash provided by (used in) financing activities	41,291,000	33,826,000	12,118,000
Net increase (decrease) in cash and cash equivalents	(5,054,000)	5,035,000	(31,636,000)
Cash and cash equivalents, beginning of period	35,042,000	30,007,000	61,643,000
Cash and cash equivalents, end of period	29,988,000	35,042,000	30,007,000
Supplemental disclosures:
Cash paid for interest	$ 953,000	358,000	543,000
Property and equipment purchases included in accounts payable		7,000
Right-of-use assets obtained in exchange of operating lease obligations		774,000	992,000
Issuance costs included in accounts payable and accrued expenses		$ 101,000	$ 45,000