Condensed Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Common Stock	Additional Paid-in Capital	Foreign Currency Translation	Minimum Benefit Retirement Liability	Retained Earnings	Non-controlling Interest	Total
Adoption of new accounting standards					$ 19,706		$ 19,706
Beginning Balance at Dec. 31, 2017	$ 40	$ 184,843	$ 4,695	$ (2,162)	333,225		520,641
Beginning Balance (in shares) at Dec. 31, 2017	39,604,000
Non-controlling interest from acquisition						$ 431	431
Stock issued from equity plans		(4,127)					(4,127)
Stock issued from equity plans (in shares)	113,000
Stock-based compensation		4,494					4,494
Stock buyback		(12,750)					(12,750)
Stock buyback (in shares)	(181,000)
Foreign currency translation			2,472				2,472
Minimum benefit retirement liability				(168)			(168)
Net income					46,479
Net Income, Non-controlling Interest						31	46,510
Ending Balance at Mar. 31, 2018	$ 40	172,460	7,167	(2,330)	399,410	462	577,209
Ending Balance (in shares) at Mar. 31, 2018	39,536,000
Beginning Balance at Dec. 31, 2017	$ 40	184,843	4,695	(2,162)	333,225		520,641
Beginning Balance (in shares) at Dec. 31, 2017	39,604,000
Stock buyback							(69,021)
Foreign currency translation							(4,679)
Minimum benefit retirement liability							(9)
Net income							127,619
Net Income, Non-controlling Interest							127,701
Ending Balance at Sep. 30, 2018	$ 39	120,628	16	(2,171)	480,550	513	599,575
Ending Balance (in shares) at Sep. 30, 2018	38,716,000
Beginning Balance at Mar. 31, 2018	$ 40	172,460	7,167	(2,330)	399,410	462	577,209
Beginning Balance (in shares) at Mar. 31, 2018	39,536,000
Stock issued from equity plans		1,552					1,552
Stock issued from equity plans (in shares)	111,000
Stock-based compensation		1,943					1,943
Stock buyback	$ (1)	(25,308)					(25,309)
Stock buyback (in shares)	(407,000)
Foreign currency translation			(6,416)				(6,416)
Minimum benefit retirement liability				132			132
Net income					46,361
Net Income, Non-controlling Interest						44	46,405
Ending Balance at Jun. 30, 2018	$ 39	150,647	751	(2,198)	445,771	506	595,516
Ending Balance (in shares) at Jun. 30, 2018	39,240,000
Stock issued from equity plans		(81)					(81)
Stock issued from equity plans (in shares)	9,000
Stock-based compensation		1,024					1,024
Stock buyback		(30,962)					(30,962)
Stock buyback (in shares)	(533,000)
Foreign currency translation			(735)				(735)
Minimum benefit retirement liability				27			27
Net income					34,779		34,779
Net Income, Non-controlling Interest						7	34,786
Ending Balance at Sep. 30, 2018	$ 39	120,628	16	(2,171)	480,550	513	599,575
Ending Balance (in shares) at Sep. 30, 2018	38,716,000
Beginning Balance at Dec. 31, 2018	$ 38	97,418	(590)	(2,859)	512,783	512	$ 607,302
Beginning Balance (in shares) at Dec. 31, 2018	38,164,000						38,164,000
Stock issued from equity plans		(1,707)					$ (1,707)
Stock issued from equity plans (in shares)	72,000
Stock-based compensation		3,199					3,199
Foreign currency translation			(1,975)				(1,975)
Minimum benefit retirement liability				(53)			(53)
Net income					15,370
Net Income, Non-controlling Interest						8	15,378
Ending Balance at Mar. 31, 2019	$ 38	98,910	(2,565)	(2,912)	528,153	520	622,144
Ending Balance (in shares) at Mar. 31, 2019	38,236,000
Beginning Balance at Dec. 31, 2018	$ 38	97,418	(590)	(2,859)	512,783	512	$ 607,302
Beginning Balance (in shares) at Dec. 31, 2018	38,164,000						38,164,000
Foreign currency translation							$ (6,281)
Minimum benefit retirement liability							102
Net income							54,677
Net Income, Non-controlling Interest							54,706
Ending Balance at Sep. 30, 2019	$ 38	101,757	(6,871)	(2,757)	567,460	541	$ 660,168
Ending Balance (in shares) at Sep. 30, 2019	38,332,000						38,332,000
Beginning Balance at Mar. 31, 2019	$ 38	98,910	(2,565)	(2,912)	528,153	520	$ 622,144
Beginning Balance (in shares) at Mar. 31, 2019	38,236,000
Stock issued from equity plans		665					665
Stock issued from equity plans (in shares)	69,000
Stock-based compensation		937					937
Foreign currency translation			543				543
Minimum benefit retirement liability				63			63
Net income					31,686
Net Income, Non-controlling Interest						11	31,697
Ending Balance at Jun. 30, 2019	$ 38	100,512	(2,022)	(2,849)	559,839	531	656,049
Ending Balance (in shares) at Jun. 30, 2019	38,305,000
Stock issued from equity plans		328					328
Stock issued from equity plans (in shares)	27,000
Stock-based compensation		917					917
Foreign currency translation			(4,849)				(4,849)
Minimum benefit retirement liability				92			92
Net income					7,621		7,621
Net Income, Non-controlling Interest						10	7,631
Ending Balance at Sep. 30, 2019	$ 38	$ 101,757	$ (6,871)	$ (2,757)	$ 567,460	$ 541	$ 660,168
Ending Balance (in shares) at Sep. 30, 2019	38,332,000						38,332,000