Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
CASH FLOWS FROM OPERATING ACTIVITIES:
Net loss	$ (6,662)	$ (10,282)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation expense	166	138
Stock-based compensation expense	846	989
Non-cash interest expense	48	53
Non-cash lease expense	277	269
Changes in operating assets and liabilities:
Prepaid expenses and other current assets	(321)	109
Accounts receivable	30	174
Accounts payable	757	262
Accrued expenses and other current liabilities	(2,226)	215
Deferred revenue	(2,816)
Net cash used in operating activities	(9,901)	(8,073)
CASH FLOWS FROM INVESTING ACTIVITIES:
Purchases of property and equipment	(7)	(151)
Net cash used in investing activities	(7)	(151)
CASH FLOWS FROM FINANCING ACTIVITIES:
Net proceeds from at-the-market common stock issuances		2,091
Principal repayments on term loan	(833)
Net cash (used in) provided by financing activities	(833)	2,091
NET DECREASE IN CASH, CASH EQUIVALENTS AND RESTRICTED CASH	(10,741)	(6,133)
Cash, cash equivalents and restricted cash at beginning of year	54,102	70,697
Cash, cash equivalents and restricted cash at end of period	43,361	64,564
RECONCILIATION OF CASH, CASH EQUIVALENTS AND RESTRICTED CASH
Cash and cash equivalents	42,739	63,942
Long-term restricted cash	622	622
Total cash, cash equivalents and restricted cash	43,361	64,564
SUPPLEMENTAL DISCLOSURE OF CASH FLOW INFORMATION:
Cash paid for interest	170	218
SUPPLEMENTAL DISCLOSURE OF NON-CASH ACTIVITIES:
Property and equipment purchases in accrued expenses and accounts payable	$ 23	$ 70