Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016
Cash flows from operating activities:
Net loss	$ (17,401)	$ (15,916)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation, amortization and write-off of property and equipment	1,024	1,016
Amortization and write-off of intangibles	775	876
Stock-based compensation	4,872	4,162
Changes in operating assets and liabilities:
Trade accounts receivable	(1,952)	2,095
Other current assets	(482)	(437)
Other assets	20	(56)
Accounts payable and other accrued liabilities	373	680
Deferred revenue	(1,247)	(1,407)
Net cash used in operating activities	(14,018)	(8,987)
Cash flows from investing activities:
Purchase of property and equipment	(1,424)	(1,565)
Capitalized patent costs	(625)	(623)
Maturity of marketable securities	41,231	35,182
Purchase of marketable securities	(27,631)	(40,817)
Net cash provided by (used in) investing activities	11,551	(7,823)
Cash flows from financing activities:
Issuance of common stock, net of issuance costs	17,698	39,700
Exercise of stock options	793	476
Purchase of common stock	(2,063)	(1,879)
Net cash provided by financing activities	16,428	38,297
Net increase in cash and cash equivalents	13,961	21,487
Cash and cash equivalents at beginning of period	11,638	3,160
Cash and cash equivalents at end of period	25,599	24,647
Supplemental disclosure of cash flow information:
Cash paid for income taxes, net	29	27
Supplemental schedule of non-cash investing activities:
Property and equipment and patent costs in accounts payable	249	(137)
Stock-based compensation capitalized to software and patent costs	$ 151	$ 121