Consolidated Statements of Changes in Stockholders' Equity - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-In Capital	Treasury Stock	Retained Earnings	Accumulated Other Non-Owner Changes to Equity
Balance at Dec. 31, 2017	$ 1,260,321	$ 630	$ 457,365	$ (297,998)	$ 1,206,723	$ (106,399)
Balance (in shares) at Dec. 31, 2017		63,034,000		9,656,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Comprehensive income	101,416				166,186	(64,770)
Dividends declared	(32,206)				(32,206)
Common stock repurchases (in shares)				2,292,100
Common stock repurchases	(138,275)			$ (138,275)
Reclassification pursuant to accounting guidance related to U.S. Tax Reform (Note 1)	0				19,331	(19,331)
Cumulative effect of change in Revenue Recognition accounting guidance (Note 1)	4,295				4,295
Employee stock plans	7,505	$ 4	13,453	$ (5,395)	(557)
Employee stock plans (in shares)		332,893		86,000
Balance at Dec. 31, 2018	1,203,056	$ 634	470,818	$ (441,668)	1,363,772	(190,500)
Balance (in shares) at Dec. 31, 2018		63,367,000		12,034,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Comprehensive income	138,355				158,350	(19,995)
Dividends declared	(32,544)				(32,544)
Common stock repurchases (in shares)				900,000
Common stock repurchases	(50,347)			$ (50,347)
Employee stock plans	12,008	$ 5	18,464	$ (6,059)	(402)
Employee stock plans (in shares)		505,623		117,000
Balance at Dec. 31, 2019	1,270,528	$ 639	489,282	$ (498,074)	1,489,176	(210,495)
Balance (in shares) at Dec. 31, 2019		63,873,000		13,051,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Comprehensive income	151,555				63,375	88,180
Dividends declared	(32,402)				(32,402)
Common stock repurchases (in shares)				396,000
Common stock repurchases	(15,550)			$ (15,550)
Employee stock plans	8,546	$ 3	12,249	$ (3,368)	(338)
Employee stock plans (in shares)		298,565		83,000
Balance at Dec. 31, 2020	$ 1,382,677	$ 642	$ 501,531	$ (516,992)	$ 1,519,811	$ (122,315)
Balance (in shares) at Dec. 31, 2020		64,171,000		13,530,000