Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Cash flows from operating activities:
Net loss	$ (8,908)	$ (8,463)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation, amortization and write-off of property and equipment	374	357
Amortization and write-off of intangibles	201	180
Stock-based compensation	2,195	2,037
Changes in operating assets and liabilities:
Trade accounts receivable	62	161
Other current assets	338	74
Other assets	136	(33)
Accounts payable and other accrued liabilities	61	800
Deferred revenue	(146)	(393)
Lease liability and other long-term liabilities	(159)	(174)
Net cash used in operating activities	(5,846)	(5,454)
Cash flows from investing activities:
Purchase of property and equipment	(235)	(194)
Capitalized patent costs	(137)	(153)
Maturity of marketable securities	11,691	6,744
Purchase of marketable securities	(6,407)	(3,559)
Net cash provided by investing activities	4,912	2,838
Cash flows from financing activities:
Issuance of common stock, net of issuance costs	574	0
Exercise of stock options	135	99
Purchase of common stock	(738)	(486)
Net cash used in financing activities	(29)	(387)
Net decrease in cash and cash equivalents	(963)	(3,003)
Cash and cash equivalents at beginning of period	11,213	27,278
Cash and cash equivalents at end of period	10,250	24,275
Supplemental disclosure of cash flow information:
Cash received (paid) for income taxes, net	16	(3)
Supplemental schedule of non-cash activities:
Property and equipment and patent costs in accounts payable	16	2
Stock-based compensation capitalized to software and patent costs	35	41
Right of use assets obtained in exchange for lease obligations	$ 0	$ 2,709