Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Cash flows from operating activities:
Net loss	$ (32,537)	$ (32,840)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation, amortization and write-off of property and equipment	1,531	1,449
Amortization and write-off of intangibles	771	758
Amortization of right of use assets under operating leases	470	447
Amortization of net premiums and (discounts) on marketable securities	(204)	710
Stock-based compensation	9,115	8,214
Changes in operating assets and liabilities:
Trade accounts receivable	114	(133)
Other current assets	259	(356)
Other assets	(8)	27
Accounts payable and other accrued liabilities	512	702
Deferred revenue	(199)	(41)
Lease liability and other long-term liabilities	(170)	(639)
Net cash used in operating activities	(20,346)	(21,702)
Cash flows from investing activities:
Purchase of property and equipment	(1,020)	(1,055)
Capitalized patent costs	(612)	(659)
Maturity of marketable securities	43,155	41,374
Purchase of marketable securities	(75,379)	(51,310)
Net cash used in investing activities	(33,856)	(11,650)
Cash flows from financing activities:
Issuance of common stock, net of issuance costs	38,603	19,615
Issuance of preferred stock, net of issuance costs	16,888
Exercise of stock options	5,922	1,178
Proceeds from note payable	5,032
Purchase of common stock	(3,760)	(3,506)
Net cash provided by financing activities	62,685	17,287
Net increase (decrease) in cash and cash equivalents	8,483	(16,065)
Cash and cash equivalents at beginning of period	11,213	27,278
Cash and cash equivalents at end of period	19,696	11,213
Supplemental disclosure of cash flow information:
Cash received for income taxes, net	20	90
Supplemental schedule of non-cash activities:
Property and equipment and patent costs in accounts payable	76	35
Stock-based compensation capitalized to software and patent costs	158	174
Right of use assets obtained in exchange for lease obligations		$ 2,709
Beneficial conversion feature	11,443
Series B preferred stock dividend, converted into common stock	$ 248