CONSOLIDATED STATEMENTS OF CHANGES IN STOCKHOLDERS' EQUITY - USD ($) $ in Thousands	Common Stock [Member]	Capital in Excess of Par Value [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Treasury Stock [Member]	Total SMP [Member]	Non-Controlling Interest [Member]	Total
Balance at beginning of period at Dec. 31, 2021	$ 47,872	$ 105,377	$ 532,319	$ (8,169)	$ (75,819)	$ 601,580	$ 11,047	$ 612,627
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net earnings (loss)	0	0	19,446	0	0	19,446	(8)	19,438
Other comprehensive income (loss), net of tax	0	0	0	(646)	0	(646)	3	(643)
Cash dividends paid	0	0	(5,935)	0	0	(5,935)	0	(5,935)
Purchase of treasury stock	0	0	0	0	(6,850)	(6,850)	0	(6,850)
Stock-based compensation	0	1,860	0	0	120	1,980	0	1,980
Employee Stock Ownership Plan	0	369	0	0	1,927	2,296	0	2,296
Balance at end of period at Mar. 31, 2022	47,872	107,606	545,830	(8,815)	(80,622)	611,871	11,042	622,913
Balance at beginning of period at Dec. 31, 2022	47,872	105,615	564,242	(12,470)	(95,239)	610,020	11,018	621,038
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net earnings (loss)	0	0	11,918	0	0	11,918	39	11,957
Other comprehensive income (loss), net of tax	0	0	0	1,469	0	1,469	(29)	1,440
Cash dividends paid	0	0	(6,261)	0	0	(6,261)	0	(6,261)
Stock-based compensation	0	1,044	0	0	488	1,532	0	1,532
Employee Stock Ownership Plan	0	16	0	0	2,950	2,966	0	2,966
Balance at end of period at Mar. 31, 2023	$ 47,872	$ 106,675	$ 569,899	$ (11,001)	$ (91,801)	$ 621,644	$ 11,028	$ 632,672