Condensed Consolidated Statements of Stockholders' Equity (Unaudited) - USD ($) $ in Thousands	Common Class A [Member] Retained Earnings [Member]	Common Class A [Member] AOCI Attributable to Parent [Member]	Common Class A [Member] Common Stock, Common Class A [Member]	Common Class A [Member] Common Stock, Common Class B [Member]	Common Class A [Member] Additional Paid-in Capital [Member]	Common Class A [Member]	Common Class B [Member] Retained Earnings [Member]	Common Class B [Member] AOCI Attributable to Parent [Member]	Common Class B [Member] Common Stock, Common Class A [Member]	Common Class B [Member] Common Stock, Common Class B [Member]	Common Class B [Member] Additional Paid-in Capital [Member]	Common Class B [Member]	Retained Earnings [Member]	AOCI Attributable to Parent [Member]	Common Stock, Common Class A [Member]	Common Stock, Common Class B [Member]	Additional Paid-in Capital [Member]	Total
Balance at Dec. 31, 2019													$ 157,063	$ (24,065)	$ 214	$ 1,013	$ 33,826	$ 168,051
Net earnings													(3,804)	0	0	0	0	(3,804)
Cash dividends declared on common stock	$ (130)	$ 0	$ 0	$ 0	$ 0	$ (130)	$ (709)	$ 0	$ 0	$ 0	$ 0	$ (709)
Forfeiture of restricted common stock													0	0	0	(1)		0
Forfeiture of restricted common stock, APIC																	1
Foreign currency translation adjustment, net of taxes													0	(2,245)	0	0	0	(2,245)
Stock-based compensation expense													0	0	0	0	603	603
Change in unfunded SERP liability, net of taxes													0	66	0	0	0	66
Balance at Mar. 31, 2020													152,420	(26,244)	214	1,012	34,430	161,832
Balance at Dec. 31, 2019													157,063	(24,065)	214	1,013	33,826	168,051
Net earnings						1,512						7,732						9,244
Cash dividends declared on common stock						(388)						(2,133)
Foreign currency translation adjustment, net of taxes																		2,020
Unrealized holding losses on marketable securities																		(1)
Change in unfunded SERP liability, net of taxes																		198
Balance at Sep. 30, 2020													163,786	(21,848)	214	1,022	35,597	178,771
Balance at Mar. 31, 2020													152,420	(26,244)	214	1,012	34,430	161,832
Net earnings													5,573	0	0	0	0	5,573
Cash dividends declared on common stock	(129)	0	0	0	0	(129)	(707)	0	0	0	0	(707)
Forfeiture of restricted common stock													0	0	0	11		0
Forfeiture of restricted common stock, APIC																	(11)
Foreign currency translation adjustment, net of taxes													0	676	0	0	0	676
Stock-based compensation expense													0	0	0	0	617	617
Change in unfunded SERP liability, net of taxes													0	66	0	0	0	66
Balance at Jun. 30, 2020													157,157	(25,502)	214	1,023	35,036	167,928
Net earnings						1,233						6,242	7,475	0	0	0	0	7,475
Cash dividends declared on common stock	(129)	0	0	0	0	(129)	(717)	0	0	0	0	(717)
Forfeiture of restricted common stock													0	0	0	(1)		0
Forfeiture of restricted common stock, APIC																	1
Foreign currency translation adjustment, net of taxes													0	3,588	0	0	0	3,588
Unrealized holding losses on marketable securities																		0
Stock-based compensation expense													0	0	0	0	560	560
Change in unfunded SERP liability, net of taxes													0	66	0	0	0	66
Balance at Sep. 30, 2020													163,786	(21,848)	214	1,022	35,597	178,771
Balance at Dec. 31, 2020													166,491	(18,063)	214	1,021	36,136	185,799
Net earnings													3,199	0	0	0	0	3,199
Cash dividends declared on common stock	(128)	0	0	0	0	(128)	(716)	0	0	0	0	(716)
Forfeiture of restricted common stock													0	0	0	(1)		0
Forfeiture of restricted common stock, APIC																	1
Foreign currency translation adjustment, net of taxes													0	(2,529)	0	0	0	(2,529)
Unrealized holding losses on marketable securities													0	(1)	0	0	0	(1)
Stock-based compensation expense													0	0	0	0	600	600
Change in unfunded SERP liability, net of taxes													0	99	0	0	0	99
Balance at Mar. 31, 2021													168,846	(20,494)	214	1,020	36,737	186,323
Balance at Dec. 31, 2020													166,491	(18,063)	214	1,021	36,136	185,799
Net earnings						2,761						14,052						16,813
Cash dividends declared on common stock						(386)						(2,149)
Foreign currency translation adjustment, net of taxes																		(1,971)
Unrealized holding losses on marketable securities																		45
Change in unfunded SERP liability, net of taxes																		299
Balance at Sep. 30, 2021													180,769	(19,690)	214	1,026	37,883	200,202
Balance at Mar. 31, 2021													168,846	(20,494)	214	1,020	36,737	186,323
Net earnings													7,880	0	0	0	0	7,880
Cash dividends declared on common stock	(129)	0	0	0	0	(129)	(714)	0	0	0	0	(714)
Forfeiture of restricted common stock													0	0	0	(1)		0
Forfeiture of restricted common stock, APIC																	1
Foreign currency translation adjustment, net of taxes													0	2,540	0	0	0	2,540
Stock-based compensation expense													0	0	0	0	598	598
Change in unfunded SERP liability, net of taxes													0	100	0	0	0	100
Issuance of restricted common stock													0	0	0	8	(8)	0
Balance at Jun. 30, 2021													175,883	(17,854)	214	1,027	37,328	196,598
Net earnings						940						4,794	5,734	0	0	0	0	5,734
Cash dividends declared on common stock	$ (129)	$ 0	$ 0	$ 0	$ 0	$ (129)	$ (719)	$ 0	$ 0	$ 0	$ 0	$ (719)
Forfeiture of restricted common stock													0	0	0	(1)		0
Forfeiture of restricted common stock, APIC																	1
Foreign currency translation adjustment, net of taxes													0	(1,982)	0	0	0	(1,982)
Unrealized holding losses on marketable securities													0	46	0	0	0	46
Stock-based compensation expense													0	0	0	0	554	554
Change in unfunded SERP liability, net of taxes													0	100	0	0	0	100
Repurchase of Class A common stock													0	0	0	0	0	0
Balance at Sep. 30, 2021													$ 180,769	$ (19,690)	$ 214	$ 1,026	$ 37,883	$ 200,202