CONDENSED CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY (Unaudited) - USD ($) $ in Thousands	Total	Class A Common Stock [Member]	Class B Common Stock [Member]	Retained Earnings [Member]	Retained Earnings [Member] Class A Common Stock [Member]	Retained Earnings [Member] Class B Common Stock [Member]	Accumulated Other Comprehensive (Loss) Income [Member]	Common Stock [Member]	Common Stock [Member] Class A Common Stock [Member]	Common Stock [Member] Class B Common Stock [Member]	Additional Paid-in Capital [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Effect of adoption of ASU | ASU 2014-09 [Member]	$ 3,497			$ 3,497
Balance at beginning of period at Dec. 31, 2017	157,960			147,807			$ (19,625)		$ 217	$ 986	$ 28,575
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net earnings (loss)	5,332	$ 901	$ 4,431	5,332				$ 0
Dividends declared		(261)	(1,390)		$ (261)	$ (1,390)
Forfeiture of restricted common stock	0									(2)	2
Foreign currency translation adjustment, net of taxes	(3,431)						(3,431)
Unrealized holding losses on marketable securities arising during the year, net of taxes	(31)						(31)
Stock-based compensation expense	1,450										1,450
Change in unfunded SERP liability, net of taxes	171						171
Balance at end of period at Jun. 30, 2018	163,297			154,985			(22,916)		217	984	30,027
Balance at beginning of period at Mar. 31, 2018	164,175			149,171			(15,553)		217	985	29,355
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net earnings (loss)	6,634	1,141	5,493	6,634				0
Dividends declared		(131)	(689)		(131)	(689)
Forfeiture of restricted common stock	0									(1)	1
Foreign currency translation adjustment, net of taxes	(7,448)						(7,448)
Unrealized holding losses on marketable securities arising during the year, net of taxes	0
Stock-based compensation expense	671										671
Change in unfunded SERP liability, net of taxes	85						85
Balance at end of period at Jun. 30, 2018	163,297			154,985			(22,916)		217	984	30,027
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Effect of adoption of ASU							(463)
Effect of adoption of ASU | ASU 2018-02 [Member]	0			463
Balance at beginning of period at Dec. 31, 2018	176,470			168,695			(24,838)		217	1,009	31,387
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net earnings (loss)	4,098	673	3,425	4,098				0
Dividends declared		(261)	(1,412)		(261)	(1,412)
Issuance of restricted common stock	0									7	(7)
Forfeiture of restricted common stock	0									(2)	2
Foreign currency translation adjustment, net of taxes	(294)						(294)
Unrealized holding losses on marketable securities arising during the year, net of taxes	0
Stock-based compensation expense	1,601										1,601
Change in unfunded SERP liability, net of taxes	74						74
Balance at end of period at Jun. 30, 2019	180,276			171,583			(25,521)		217	1,014	32,983
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Effect of adoption of ASU | ASU 2018-02 [Member]				463			(463)
Balance at beginning of period at Mar. 31, 2019	178,153			169,451			(24,724)		217	1,008	32,201
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net earnings (loss)	2,967	494	2,473	2,967				$ 0
Dividends declared		$ (131)	$ (704)		$ (131)	$ (704)
Issuance of restricted common stock	0									7	(7)
Forfeiture of restricted common stock	0									(1)	1
Foreign currency translation adjustment, net of taxes	(834)						(834)
Unrealized holding losses on marketable securities arising during the year, net of taxes	0
Stock-based compensation expense	788										788
Change in unfunded SERP liability, net of taxes	37						37
Balance at end of period at Jun. 30, 2019	$ 180,276			$ 171,583			(25,521)		$ 217	$ 1,014	$ 32,983
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Effect of adoption of ASU | ASU 2018-02 [Member]							$ (463)