Condensed Consolidated Balance Sheets (Unaudited) (Parentheticals) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Accounts receivable, allowance for doubtful accounts	$ 349	$ 241
Accumulated depreciation	$ 69,859	$ 69,662
Preferred stock, par value (in dollars per share)	$ 1	$ 1
Preferred stock, shares authorized (in shares)	1,000,000	1,000,000
Common stock, par value (in dollars per share)	$ 1	$ 1
Common stock, shares authorized (in shares)	25,000,000	25,000,000
Common stock, shares issued (in shares)	12,121,484	12,121,484
Common stock, shares outstanding (in shares)	6,666,984	6,599,309
Treasury stock, shares (in shares)	5,454,500	5,522,175
Series A Preferred Stock [Member]
Preferred stock, shares issued (in shares)	9,926	9,926
Preferred stock, shares outstanding (in shares)	9,926	9,926