Consolidated Statements of Stockholders' Equity - USD ($) shares in Thousands, $ in Thousands	Common Stock	Treasury Stock	Additional Paid-in Capital	Accumulated Other Comprehensive Income (Loss)	Retained Earnings	Total
Beginning Balance at Dec. 31, 2018	$ 527	$ (125,452)	$ 256,806	$ (453)	$ 1,082,169	$ 1,213,597
Beginning Balance, Shares at Dec. 31, 2018	52,690	4,489
Comprehensive income				(271)	124,355	124,084
Common stock purchased for treasury		$ (10,340)				(10,340)
Common stock acquired, shares		111
Restricted shares forfeited, Shares		14
Share-based compensation	$ 1	$ (8,127)	5,184			(2,942)
Share-based compensation, Shares	152	68
Exercise of stock options	$ 2		3,406			3,408
Exercise of stock options, Shares	191
Ending Balance at Jun. 30, 2019	$ 530	$ (143,919)	265,396	$ (724)	1,206,524	1,327,807
Ending Balance, Shares at Jun. 30, 2019	53,033	4,682
Beginning Balance at Dec. 31, 2019	$ 531	$ (169,365)	270,923		1,341,344	1,443,433
Beginning Balance, Shares at Dec. 31, 2019	53,054	4,949
Comprehensive income					118,395	118,395
Common stock purchased for treasury		$ (69,048)				(69,048)
Common stock acquired, shares		898
Restricted shares forfeited, Shares		10
Share-based compensation	$ 1	$ (4,969)	5,333			365
Share-based compensation, Shares	167	62
Exercise of stock options			74			74
Exercise of stock options, Shares	4
Ending Balance at Jun. 30, 2020	$ 532	$ (243,382)	$ 276,330		1,455,907	1,489,387
Ending Balance, Shares at Jun. 30, 2020	53,225	5,919
Cumulative effect from the adoption of accounting pronouncements, net of taxes					$ (3,832)	$ (3,832)