SIGNIFICANT ACCOUNTING POLICIES - Dividends, Advertising and Marketable securities (Details) - USD ($)	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Accounting policies:
Prepaid expenses related to unamortized product brochure costs	$ 194,000	$ 269,000
Net realized (losses) gains on marketable securities		4,000	$ (81,000)
Net realized gain		4,000	(81,000)
Selling, general and administrative expenses
Accounting policies:
Advertising expenses	$ 2,013,000	$ 2,543,000	$ 2,468,000
Dividend declared
Accounting policies:
Amount of dividend payable in cash per share	$ 0.10
Dividends payable, date declared	Jan. 26, 2021
Dividend payable, date to be payable	Mar. 10, 2021
Dividends payable, date of record	Feb. 10, 2021

Amount charged to advertising expense for the period, which are expenses incurred with the objective of increasing revenue for a specified brand, product or product line.

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