Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Common Stock	Additional Paid-in Capital	Foreign Currency Translation	Unrealized Gain (Loss)on Marketable Securities	Minimum Benefit Retirement Liability	Retained Earnings	Non-controlling Interest	Total
Beginning Balance at Dec. 31, 2016	$ 40	$ 203,603	$ (3,610)	$ 2	$ (3,325)	$ 195,364		$ 392,074
Beginning Balance (in shares) at Dec. 31, 2016	39,712,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock issued from equity plans		(1,316)						(1,316)
Stock issued from equity plans (in shares)	314,000
Stock-based compensation		12,549						12,549
Stock buyback		(29,993)						(29,993)
Stock buyback (in shares)	(422,000)
Foreign currency translation			8,305					8,305
Unrealized loss on marketable securities				(2)				(2)
Minimum benefit retirement liability					1,163			1,163
Net income						137,861		137,861
Comprehensive income			8,305	$ (2)	1,163	137,861		147,327
Ending Balance at Dec. 31, 2017	$ 40	184,843	4,695		(2,162)	333,225		520,641
Ending Balance (in shares) at Dec. 31, 2017	39,604,000
Adoption of new accounting standards						32,533		32,533
Non-controlling interest from acquisition							$ 426	426
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock issued from equity plans		(2,005)						(2,005)
Stock issued from equity plans (in shares)	256,000
Stock-based compensation		9,703						9,703
Stock buyback	$ (2)	(95,123)						(95,125)
Stock buyback (in shares)	(1,696,000)
Foreign currency translation			(5,285)					(5,285)
Minimum benefit retirement liability					(697)			(697)
Net income						147,025	86	147,111
Comprehensive income			(5,285)		(697)	147,025	86	141,129
Ending Balance at Dec. 31, 2018	$ 38	97,418	(590)		(2,859)	512,783	512	$ 607,302
Ending Balance (in shares) at Dec. 31, 2018	38,164,000							38,164,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock issued from equity plans		104						$ 104
Stock issued from equity plans (in shares)	194,000
Stock-based compensation		7,327						7,327
Foreign currency translation			(2,523)					(2,523)
Minimum benefit retirement liability					75			75
Net income						64,941	34	64,975
Comprehensive income			(2,523)		75	64,941	34	62,527
Ending Balance at Dec. 31, 2019	$ 38	$ 104,849	$ (3,113)		$ (2,784)	$ 577,724	$ 546	$ 677,260
Ending Balance (in shares) at Dec. 31, 2019	38,358,000							38,358,000