Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Cash flows from operating activities:
Net loss	$ (8,408)	$ (16,687)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization expense	1,914	1,590
Amortization of right of use of assets	561
Amortization of deferred rent		12
Stock-based compensation expense	217	463
Provision for doubtful accounts, net	(207)	159
Write-down of inventory to net realizable value	891	787
Loss on disposal of assets	34	1
Deferred income taxes		6,531
Changes in operating assets and liabilities:
Receivables	1,511	835
Inventories	3,565	155
Prepaid expenses and other assets	(4,148)	43
Accounts payable	(858)	(392)
Accrued liabilities	627	184
Income taxes payable	368	(258)
Deferred product revenue	(110)	(8)
Operating lease liabilities	(557)
Other long-term liabilities	(56)	(36)
Net cash used in operating activities	(4,656)	(6,621)
Cash flows from investing activities:
Capitalized patent defense costs	(5,086)	(4,698)
Purchase of property and equipment	(205)	(336)
Purchase of intangible assets	(76)	(101)
Proceeds from maturities and sales of marketable securities	9,243	10,516
Purchase of marketable securities	(9,003)	(2,230)
Net cash provided by (used in) investing activities	(5,127)	3,151
Cash flows from financing activities:
Issuance of common stock		9,883
Net proceeds from issuance of senior convertible notes	2,654
Net proceeds from equity-based compensation programs	23	39
Dividend payments		(583)
Payments for stock repurchases		(147)
Net cash provided by financing activities	2,677	9,192
Effect of exchange rate changes on cash and cash equivalents	(41)	(82)
Net increase (decrease) in cash and cash equivalents	(7,147)	5,640
Cash and cash equivalents at the beginning of the year	11,211	5,571
Cash and cash equivalents at the end of the year	4,064	11,211
Supplemental disclosure of cash flow information:
Cash paid for income taxes	$ 1	$ 11