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	0	0	38,572	0	0	38,572	77	38,649
Other comprehensive income, net of tax	0	0	0	(7,009)	0	(7,009)	(61)	(7,070)
Cash dividends paid	0	0	(11,822)	0	0	(11,822)	0	(11,822)
Purchase of treasury stock	0	0	0	0	(26,496)	(26,496)	0	(26,496)
Stock-based compensation	0	3,371	0	0	1,094	4,465	0	4,465
Employee Stock Ownership Plan	0	369	0	0	1,927	2,296	0	2,296
Balance at end of period at Jun. 30, 2022	47,872	109,117	559,069	(15,178)	(99,294)	601,586	11,063	612,649
Balance at beginning of period at Mar. 31, 2022	47,872	107,606	545,830	(8,815)	(80,622)	611,871	11,042	622,913
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net earnings	0	0	19,126	0	0	19,126	85	19,211
Other comprehensive income, net of tax	0	0	0	(6,363)	0	(6,363)	(64)	(6,427)
Cash dividends paid	0	0	(5,887)	0	0	(5,887)	0	(5,887)
Purchase of treasury stock	0	0	0	0	(19,646)	(19,646)	0	(19,646)
Stock-based compensation	0	1,511	0	0	974	2,485	0	2,485
Balance at end of period at Jun. 30, 2022	47,872	109,117	559,069	(15,178)	(99,294)	601,586	11,063	612,649
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	0	0	21,055	0	0	21,055	89	21,144
Other comprehensive income, net of tax	0	0	0	4,543	0	4,543	(110)	4,433
Cash dividends paid	0	0	(12,544)	0	0	(12,544)	0	(12,544)
Dividends paid to noncontrolling interest	0	0	0	0	0	0	(255)	(255)
Stock-based compensation	0	898	0	0	2,735	3,633	0	3,633
Employee Stock Ownership Plan	0	16	0	0	2,950	2,966	0	2,966
Balance at end of period at Jun. 30, 2023	47,872	106,529	572,753	(7,927)	(89,554)	629,673	10,742	640,415
Balance at beginning of period at Mar. 31, 2023	47,872	106,675	569,899	(11,001)	(91,801)	621,644	11,028	632,672
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net earnings	0	0	9,137	0	0	9,137	50	9,187
Other comprehensive income, net of tax	0	0	0	3,074	0	3,074	(81)	2,993
Cash dividends paid	0	0	(6,283)	0	0	(6,283)	0	(6,283)
Dividends paid to noncontrolling interest	0	0	0	0	0	0	(255)	(255)
Stock-based compensation	0	(146)	0	0	2,247	2,101	0	2,101
Balance at end of period at Jun. 30, 2023	$ 47,872	$ 106,529	$ 572,753	$ (7,927)	$ (89,554)	$ 629,673	$ 10,742	$ 640,415