Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Cash flows from operating activities:
Net loss	$ (21,672)	$ (17,934)	$ (15,820)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation, amortization and write-off of property and equipment	1,336	1,237	974
Amortization and write-off of intangibles	1,121	1,196	1,340
Changes in allowance for doubtful accounts		(7)	(23)
Stock-based compensation	5,553	5,077	5,403
Deferred income taxes			2,085
Changes in operating assets and liabilities:
Trade accounts receivable	(462)	(64)	1,316
Other current assets	(208)	1,124	(1,028)
Other assets	7	40	192
Accounts payable and other accrued liabilities	637	125	(635)
Deferred revenue	(176)	(534)	(537)
Net cash used in operating activities	(13,864)	(9,740)	(6,733)
Cash flows from investing activities:
Purchase of property and equipment	(1,837)	(1,218)	(1,399)
Capitalized patent costs	(790)	(895)	(1,190)
Maturity of marketable securities	41,052	42,264	28,074
Purchase of marketable securities	(53,914)	(45,340)	(29,871)
Net cash used in investing activities	(15,489)	(5,189)	(4,386)
Cash flows from financing activities:
Issuance of common stock, net of issuance costs	39,700	12,896	15,989
Exercise of stock options	668	1,514	1,487
Purchase of common stock	(2,537)	(2,443)	(2,392)
Cash dividends paid			(1,654)
Net cash provided by financing activities	37,831	11,967	13,430
Net increase (decrease) in cash and cash equivalents	8,478	(2,962)	2,311
Cash and cash equivalents at beginning of period	3,160	6,122	3,811
Cash and cash equivalents at end of period	11,638	3,160	6,122
Supplemental disclosure of cash flow information:
Cash received (paid) for income taxes, net	(38)	1,233	263
Supplemental schedule of non-cash investing activities:
Property and equipment and patent costs in accounts payable	35	73	140
Stock-based compensation capitalized to software and patent costs	$ 164	$ 174	$ 177