Condensed Consolidated Statements of Stockholders' Equity (Unaudited) - USD ($) $ in Thousands	Common Stock [Member]	Additional Paid-in Capital [Member]	Retained Earnings [Member]	Treasury Stock [Member]	Total
Balances at Dec. 31, 2019	$ 1,671	$ 374,049	$ 4,592,938	$ (2,701,629)	$ 2,267,029
Net earnings	0	0	226,532	0	226,532
Cash dividend declared and paid	0	0	(57,175)	0	(57,175)
Purchase of treasury shares	0	0	0	(75,193)	(75,193)
Share-based compensation	0	34,065	0	0	34,065
Restricted share issuances, net of stock repurchased for payroll taxes and other	0	(5,461)	0	1,046	(4,415)
Balances at Jun. 30, 2020	1,671	402,653	4,762,295	(2,775,776)	2,390,843
Balances at Mar. 31, 2020	1,671	388,577	4,669,084	(2,776,914)	2,282,418
Net earnings	0	0	121,698	0	121,698
Cash dividend declared and paid	0	0	(28,487)	0	(28,487)
Purchase of treasury shares	0	0	0	0	0
Share-based compensation	0	16,002	0	0	16,002
Restricted share issuances, net of stock repurchased for payroll taxes and other	0	(1,926)	0	1,138	(788)
Balances at Jun. 30, 2020	1,671	402,653	4,762,295	(2,775,776)	2,390,843
Balances at Dec. 31, 2020	1,671	408,244	4,984,739	(2,794,516)	2,600,138
Net earnings	0	0	318,768	0	318,768
Cash dividend declared and paid	0	0	(61,301)	0	(61,301)
Purchase of treasury shares	0	0	0	(86,580)	(86,580)
Share-based compensation	0	31,466	0	0	31,466
Restricted share issuances, net of stock repurchased for payroll taxes and other	0	(2,974)	0	(489)	(3,463)
Balances at Jun. 30, 2021	1,671	436,736	5,242,206	(2,881,585)	2,799,028
Balances at Mar. 31, 2021	1,671	419,251	5,101,748	(2,800,604)	2,722,066
Net earnings	0	0	172,162	0	172,162
Cash dividend declared and paid	0	0	(31,704)	0	(31,704)
Purchase of treasury shares	0	0	0	(81,341)	(81,341)
Share-based compensation	0	16,498	0	0	16,498
Restricted share issuances, net of stock repurchased for payroll taxes and other	0	987	0	360	1,347
Balances at Jun. 30, 2021	$ 1,671	$ 436,736	$ 5,242,206	$ (2,881,585)	$ 2,799,028