Consolidated statement of changes in stockholders' equity - USD ($) shares in Thousands, $ in Thousands	Total	Common Stock [Member] Class A Common Stock [Member]	Common Stock [Member] Class B Common Stock [Member]	Additional Paid-In Capital [Member]	Accumulated Deficit [Member]	Accumulated Other Comprehensive Loss [Member]
Beginning balance at Dec. 31, 2017	$ 60,591	$ 2	$ 4	$ 232,156	$ (166,499)	$ (5,072)
Beginning balance (in shares) at Dec. 31, 2017		26,725	36,508
Net income	24,684				24,684
Adjustment for acquisitions	(96)			(96)
Exercise of stock options	301	$ 1		300
Exercise of stock options (in shares)		632
Stock-based compensation	216			216
Foreign currency translation, net of tax	1,255					1,255
Retirement related benefit plans, net of tax	(12)					(12)
Ending balance at Mar. 31, 2018	157,718	$ 3	$ 4	232,576	(71,036)	(3,829)
Ending balance (in shares) at Mar. 31, 2018		27,357	36,508
Cumulative effect of an accounting change	70,779				70,779
Beginning balance at Dec. 31, 2018	286,782	$ 4	$ 3	379,832	(82,005)	(11,052)
Beginning balance (in shares) at Dec. 31, 2018		38,349	32,171
Net income	13,019				13,019
Exercise of stock options	458			458
Exercise of stock options (in shares)		397
Vesting of restricted stock (in shares)		14
Stock-based compensation	869			869
Foreign currency translation, net of tax	337					337
Retirement related benefit plans, net of tax	228					228
Ending balance at Mar. 31, 2019	$ 301,693	$ 4	$ 3	$ 381,159	$ (68,986)	$ (10,487)
Ending balance (in shares) at Mar. 31, 2019		38,760	32,171