Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Common Stock [Member]	Additional Paid-in Capital [Member]	Retained Earnings [Member]	Treasury Stock [Member]	Total
Balances at Dec. 31, 2016	$ 1,671	$ 293,087	$ 3,218,943	$ (2,099,640)	$ 1,414,061
Comprehensive income:
Net earnings	0	0	686,263	0	686,263
Cash dividend declared and paid	0	0	(101,362)	0	(101,362)
Purchase of treasury shares	0	0	0	(179,813)	(179,813)
Share-based compensation	0	38,291	0	0	38,291
Restricted share issuances, net of stock repurchased for payroll taxes and other	0	(20,567)	0	2,452	(18,115)
Balances at Dec. 31, 2017	1,671	310,811	3,803,844	(2,277,001)	1,839,325
Comprehensive income:
Net earnings	0	0	489,585	0	489,585
Cash dividend declared and paid	0	0	(104,994)	0	(104,994)
Purchase of treasury shares	0	0	0	(150,338)	(150,338)
Share-based compensation	0	47,369	0	0	47,369
Restricted share issuances, net of stock repurchased for payroll taxes and other	0	(17,723)	0	(1,840)	(19,563)
Balances at Dec. 31, 2018	1,671	340,457	4,188,435	(2,429,179)	2,101,384
Comprehensive income:
Net earnings	0	0	516,320	0	516,320
Cash dividend declared and paid	0	0	(111,817)	0	(111,817)
Purchase of treasury shares	0	0	0	(275,657)	(275,657)
Share-based compensation	0	53,324	0	0	53,324
Restricted share issuances, net of stock repurchased for payroll taxes and other	0	(19,732)	0	3,207	(16,525)
Balances at Dec. 31, 2019	$ 1,671	$ 374,049	$ 4,592,938	$ (2,701,629)	$ 2,267,029