Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019
Cash flows from operating activities:
Net loss	$ (16,369)	$ (16,396)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation, amortization and write-off of property and equipment	745	747
Amortization and write-off of intangibles	431	372
Stock-based compensation	4,522	4,053
Changes in operating assets and liabilities:
Trade accounts receivable	445	(351)
Other current assets	361	(40)
Other assets	318	77
Accounts payable and other accrued liabilities	(155)	1,132
Deferred revenue	(500)	(244)
Lease liability and other long-term liabilities	24	(325)
Net cash used in operating activities	(10,178)	(10,975)
Cash flows from investing activities:
Purchase of property and equipment	(456)	(404)
Capitalized patent costs	(311)	(359)
Maturity of marketable securities	26,535	14,671
Purchase of marketable securities	(19,490)	(15,085)
Net cash provided by (used in) investing activities	6,278	(1,177)
Cash flows from financing activities:
Proceeds from note payable	5,032	0
Issuance of common stock, net of issuance costs	574	19,615
Exercise of stock options	135	293
Purchase of common stock	(1,120)	(1,868)
Net cash provided by financing activities	4,621	18,040
Net increase in cash and cash equivalents	721	5,888
Cash and cash equivalents at beginning of period	11,213	27,278
Cash and cash equivalents at end of period	11,934	33,166
Supplemental disclosure of cash flow information:
Cash received for income taxes, net	12	93
Supplemental schedule of non-cash activities:
Property and equipment and patent costs in accounts payable	(26)	(7)
Stock-based compensation capitalized to software and patent costs	85	90
Right of use assets obtained in exchange for lease obligations	$ 0	$ 2,709