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 Income [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)	(1,303)	$ (240)	$ (1,063)	(1,303)
Dividends declared		(130)	(700)		$ (130)	$ (700)
Forfeiture of restricted common stock	0								(1)	1
Foreign currency translation adjustment, net of taxes	4,017						4,017
Unrealized holding losses on marketable securities arising during the year, net of taxes	(31)						(31)
Stock-based compensation expense	779									779
Change in unfunded SERP liability, net of taxes	86						86
Balance at end of period at Mar. 31, 2018	164,175			149,171			(15,553)	217	985	29,355
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Effect of adoption of ASU | ASU 2018-02 [Member]	0			463			(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)	1,131	180	951	1,131
Dividends declared		$ (130)	$ (708)		$ (130)	$ (708)
Forfeiture of restricted common stock	0								(1)	1
Foreign currency translation adjustment, net of taxes	540						540
Unrealized holding losses on marketable securities arising during the year, net of taxes	0
Stock-based compensation expense	813									813
Change in unfunded SERP liability, net of taxes	37						37
Balance at end of period at Mar. 31, 2019	$ 178,153			$ 169,451			(24,724)	$ 217	$ 1,008	$ 32,201
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Effect of adoption of ASU | ASU 2018-02 [Member]							$ (463)