CONSOLIDATED STATEMENT 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, 2020	$ 47,872	$ 105,084	$ 463,612	$ (5,676)	$ (60,656)	$ 550,236	$ 0	$ 550,236
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net earnings (loss)	0	0	21,000	0	0	21,000	0	21,000
Other comprehensive income, net of tax	0	0	0	(1,921)	0	(1,921)	0	(1,921)
Cash dividends paid	0	0	(5,588)	0	0	(5,588)	0	(5,588)
Purchase of treasury stock	0	0	0	0	(11,096)	(11,096)	0	(11,096)
Stock-based compensation	0	1,148	0	0	648	1,796	0	1,796
Employee Stock Ownership Plan	0	134	0	0	2,379	2,513	0	2,513
Balance at end of period at Mar. 31, 2021	47,872	106,366	479,024	(7,597)	(68,725)	556,940	0	556,940
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, 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