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, 2018	$ 1,671	$ 340,457	$ 4,188,435	$ (2,429,179)	$ 2,101,384
Comprehensive income:
Net earnings	0	0	119,601	0	119,601
Cash dividend declared and paid	0	0	(28,272)	0	(28,272)
Share-based compensation	0	13,571	0	0	13,571
Restricted share issuances, net of stock repurchased for payroll taxes	0	(2,147)	0	(373)	(2,520)
Balances at Dec. 31, 2018	1,671	340,457	4,188,435	(2,429,179)	2,101,384
Balances at Mar. 31, 2019	1,671	351,881	4,279,764	(2,429,552)	2,203,764
Balances at Dec. 31, 2019	1,671	374,049	4,592,938	(2,701,629)	2,267,029
Comprehensive income:
Net earnings	0	0	104,834	0	104,834
Cash dividend declared and paid	0	0	(28,688)	0	(28,688)
Share-based compensation	0	18,063	0	0	18,063
Restricted share issuances, net of stock repurchased for payroll taxes	0	(3,535)	0	(92)	(3,627)
Balances at Dec. 31, 2019	1,671	374,049	4,592,938	(2,701,629)	2,267,029
Comprehensive income:
Purchase of treasury shares	0	0	0	(75,193)	(75,193)
Balances at Mar. 31, 2020	$ 1,671	$ 388,577	$ 4,669,084	$ (2,776,914)	$ 2,282,418