CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY - 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] Class A Common Stock [Member]	Common Stock [Member] Class B Common Stock [Member]	Additional Paid-in Capital [Member]
Balance at Dec. 31, 2014	$ 224,273			$ 213,409			$ (11,948)	$ 217	$ 969	$ 21,626
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cash dividends declared on common stock		$ (522)	$ (2,713)		$ (522)	$ (2,713)
Issuance of restricted common stock	0								8	(8)
Forfeiture of restricted common stock	0								(7)	7
Foreign currency translation adjustment, net of taxes	(9,954)						(9,954)
Unrealized holding gains on marketable securities arising during the year net of taxes	5						5
Stock-based compensation expense	2,815									2,815
Change in unfunded SERP liability, net of taxes	21						21
Net (loss) earnings	19,197	3,331	15,866	19,197
Balance at Dec. 31, 2015	233,122			229,371			(21,876)	217	970	24,440
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cash dividends declared on common stock		(522)	(2,728)		(522)	(2,728)
Issuance of restricted common stock	0								18	(18)
Forfeiture of restricted common stock	0								(3)	3
Foreign currency translation adjustment, net of taxes	(9,671)						(9,671)
Unrealized holding gains on marketable securities arising during the year net of taxes	(10)						(10)
Stock-based compensation expense	2,817									2,817
Change in unfunded SERP liability, net of taxes	260						260
Net (loss) earnings	(64,834)	(11,408)	(53,426)	(64,834)
Balance at Dec. 31, 2016	158,434			161,287			(31,297)	217	985	27,242
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Reclassification of APIC pool upon adoption of ASU 2016-09 | ASU 2016-09 [Member]	0			1,696						(1,696)
Cash dividends declared on common stock		(522)	(2,757)		$ (522)	$ (2,757)
Issuance of restricted common stock	0								5	(5)
Forfeiture of restricted common stock	0								(4)	4
Foreign currency translation adjustment, net of taxes	12,439						12,439
Unrealized holding gains on marketable securities arising during the year net of taxes	(279)						(279)
Stock-based compensation expense	3,030									3,030
Change in unfunded SERP liability, net of taxes	(488)						(488)
Net (loss) earnings	(11,897)	$ (2,113)	$ (9,784)	(11,897)
Balance at Dec. 31, 2017	$ 157,960			$ 147,807			$ (19,625)	$ 217	$ 986	$ 28,575