Condensed Consolidated Statements of Cash Flows - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
OPERATING ACTIVITIES
Net income	$ 968,000	$ 7,016,000
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation	453,000	418,000
Amortization of finite-lived intangible assets	75,000	75,000
Loss from equity investment in unconsolidated subsidiary	262,000	16,000
Stock-based compensation	790,000	112,000
Deferred income tax expense (benefit)	255,000	(3,180,000)
(Gain) on marketable securities	(139,000)	(206,000)
Changes in operating assets and liabilities:
Decrease (increase) in accounts receivable, net	323,000	(1,051,000)
Decrease (increase) in inventories, net	736,000	(1,550,000)
Decrease (increase) in prepaid expenses and other assets	194,000	(225,000)
(Decrease) increase in accounts payable, accrued compensation and commissions expense and other	(725,000)	1,241,000
Net cash provided by operating activities	3,192,000	2,666,000
INVESTING ACTIVITIES
Purchase of marketable securities	(21,000)	(5,050,000)
Equity investment in unconsolidated subsidiary		(3,350,000)
Capital expenditures	(407,000)	(1,163,000)
Proceeds from sale of marketable securities		3,400,000
Net cash used in investing activities	(428,000)	(6,163,000)
FINANCING ACTIVITIES
Proceeds from issuance of at-the-market stock sales	3,254,000
Share-related issuance costs	(202,000)
Net proceeds from stock option exercise	62,000	442,000
Net cash provided by financing activities	3,114,000	442,000
Increase (decrease) in cash and cash equivalents	5,878,000	(3,055,000)
Cash and cash equivalents at beginning of year	12,453,000	15,508,000
Cash and cash equivalents at end of year	18,331,000	12,453,000
Supplemental Disclosure:
Cash paid for interest	3,000	6,000
Cash paid for income taxes	$ 60,000	$ 86,000