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, 2017	$ 1,671	$ 310,811	$ 3,803,844	$ (2,277,001)	$ 1,839,325
Comprehensive income:
Net earnings	0	0	269,794	0	269,794
Cash dividend declared and paid	0	0	(52,583)	0	(52,583)
Purchase of treasury shares	0	0	0	(50,027)	(50,027)
Share-based compensation	0	26,001	0	0	26,001
Restricted share issuances, net of stock repurchased for payroll taxes and other	0	478	0	374	852
Balances at Dec. 31, 2017	1,671	310,811	3,803,844	(2,277,001)	1,839,325
Balances at Jun. 30, 2018	1,671	337,290	4,021,055	(2,326,654)	2,033,362
Balances at Mar. 31, 2018	1,671	322,711	3,895,645	(2,276,964)	1,943,063
Comprehensive income:
Net earnings	0	0	151,652	0	151,652
Cash dividend declared and paid	0	0	(26,242)	0	(26,242)
Purchase of treasury shares	0	0	0	(50,027)	(50,027)
Share-based compensation	0	13,965	0	0	13,965
Restricted share issuances, net of stock repurchased for payroll taxes and other	0	614	0	337	951
Balances at Mar. 31, 2018	1,671	322,711	3,895,645	(2,276,964)	1,943,063
Balances at Jun. 30, 2018	1,671	337,290	4,021,055	(2,326,654)	2,033,362
Balances at Dec. 31, 2018	1,671	340,457	4,188,435	(2,429,179)	2,101,384
Comprehensive income:
Net earnings	0	0	253,234	0	253,234
Cash dividend declared and paid	0	0	(56,278)	0	(56,278)
Purchase of treasury shares	0	0	0	(189,734)	(189,734)
Share-based compensation	0	28,304	0	0	28,304
Restricted share issuances, net of stock repurchased for payroll taxes and other	0	(1,595)	0	41	(1,554)
Balances at Dec. 31, 2018	1,671	340,457	4,188,435	(2,429,179)	2,101,384
Balances at Jun. 30, 2019	1,671	367,166	4,385,391	(2,618,872)	2,135,356
Balances at Mar. 31, 2019	1,671	351,881	4,279,764	(2,429,552)	2,203,764
Comprehensive income:
Net earnings	0	0	133,633	0	133,633
Cash dividend declared and paid	0	0	(28,006)	0	(28,006)
Purchase of treasury shares	0	0	0	(189,734)	(189,734)
Share-based compensation	0	14,732	0	0	14,732
Restricted share issuances, net of stock repurchased for payroll taxes and other	0	553	0	414	967
Balances at Mar. 31, 2019	1,671	351,881	4,279,764	(2,429,552)	2,203,764
Balances at Jun. 30, 2019	$ 1,671	$ 367,166	$ 4,385,391	$ (2,618,872)	$ 2,135,356