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, 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	0	0	47,418	0	0	47,418	129	47,547
Other comprehensive income, net of tax	0	0	0	(10,976)	0	(10,976)	(176)	(11,152)
Cash dividends paid	0	0	(17,602)	0	0	(17,602)	0	(17,602)
Purchase of treasury stock	0	0	0	0	(29,656)	(29,656)	0	(29,656)
Stock-based compensation	0	(1,335)	0	0	7,662	6,327	0	6,327
Employee Stock Ownership Plan	0	369	0	0	1,927	2,296	0	2,296
Balance at end of period at Sep. 30, 2022	47,872	104,411	562,135	(19,145)	(95,886)	599,387	11,000	610,387
Balance at beginning of period at Jun. 30, 2022	47,872	109,117	559,069	(15,178)	(99,294)	601,586	11,063	612,649
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net earnings	0	0	8,846	0	0	8,846	52	8,898
Other comprehensive income, net of tax	0	0	0	(3,967)	0	(3,967)	(115)	(4,082)
Cash dividends paid	0	0	(5,780)	0	0	(5,780)	0	(5,780)
Purchase of treasury stock	0	0	0	0	(3,160)	(3,160)	0	(3,160)
Stock-based compensation	0	(4,706)	0	0	6,568	1,862	0	1,862
Balance at end of period at Sep. 30, 2022	47,872	104,411	562,135	(19,145)	(95,886)	599,387	11,000	610,387
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]
Noncontrolling interest in step acquisition	0	0	0	0	0	0	5,273	5,273
Net earnings	0	0	27,714	0	0	27,714	152	27,866
Other comprehensive income, net of tax	0	0	0	2,251	0	2,251	(63)	2,188
Cash dividends paid	0	0	(18,846)	0	0	(18,846)	0	(18,846)
Dividends paid to noncontrolling interest	0	0	0	0	0	0	(255)	(255)
Stock-based compensation	0	2,427	0	0	2,816	5,243	0	5,243
Employee Stock Ownership Plan	0	16	0	0	2,950	2,966	0	2,966
Balance at end of period at Sep. 30, 2023	47,872	108,058	573,110	(10,219)	(89,473)	629,348	16,125	645,473
Balance at beginning of period at Jun. 30, 2023	47,872	106,529	572,753	(7,927)	(89,554)	629,673	10,742	640,415
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Noncontrolling interest in step acquisition	0	0	0	0	0	0	5,273	5,273
Net earnings	0	0	6,659	0	0	6,659	63	6,722
Other comprehensive income, net of tax	0	0	0	(2,292)	0	(2,292)	47	(2,245)
Cash dividends paid	0	0	(6,302)	0	0	(6,302)	0	(6,302)
Stock-based compensation	0	1,529	0	0	81	1,610	0	1,610
Balance at end of period at Sep. 30, 2023	$ 47,872	$ 108,058	$ 573,110	$ (10,219)	$ (89,473)	$ 629,348	$ 16,125	$ 645,473