Consolidated Statement of Changes in Shareholders' Equity (Unaudited) - USD ($) $ in Thousands	Total	Preferred Stock [Member]	Common Stock [Member]	Common Stock Issuable [Member]	Additional Paid-in Capital [Member]	Additional Paid-in Capital [Member] Series A Warrants [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Income (Loss), Net [Member]	Treasury Stock [Member]	Treasury Stock [Member] Series A Warrants [Member]
Beginning balance at Dec. 31, 2016	$ 16,486,622	$ 1,231,500	$ 79,973	$ 2,145	$ 6,676,948		$ 9,222,488	$ (294,636)	$ (431,796)
Total comprehensive income	351,996						348,927	3,069
Preferred stock cash dividends	(18,237)						(18,237)
Exercise of stock warrants into common stock						$ (5,934)				$ 5,934
Purchases of treasury stock	(532,073)								(532,073)
Stock-based compensation plans:
Compensation expense, net	(11,409)		(60)		(67,016)				55,667
Exercises of stock options, net	40,662				(3,127)				43,789
Stock purchase plan	10,831				2,563				8,268
Directors’ stock plan	473				126				347
Deferred compensation plans, net, including dividend equivalents	(54)			(224)	(205)		(21)		396
Common stock cash dividends	(115,707)						(115,707)
Ending balance at Mar. 31, 2017	16,213,104	1,231,500	79,913	1,921	6,603,355		9,437,450	(291,567)	(849,468)
Beginning balance at Dec. 31, 2017	16,250,819	1,231,500	79,909	1,847	6,590,855		10,164,804	(363,814)	(1,454,282)
Cumulative effect of change in accounting principles- equity securities	(16,853)						16,853	(16,853)
Total comprehensive income	250,034						352,610	(102,576)
Preferred stock cash dividends	(18,130)						(18,130)
Exercise of stock warrants into common stock						$ (3,455)				$ 3,455
Purchases of treasury stock	(720,966)								(720,966)
Stock-based compensation plans:
Compensation expense, net	5,833		(25)		(15,362)				21,220
Exercises of stock options, net	42,100				(1,945)				44,045
Stock purchase plan	11,124				2,358				8,766
Directors’ stock plan	589				74				515
Deferred compensation plans, net, including dividend equivalents	(48)			(172)	(244)		(18)		386
Common stock cash dividends	(111,661)						(111,661)
Ending balance at Mar. 31, 2018	$ 15,709,694	$ 1,231,500	$ 79,884	$ 1,675	$ 6,572,281		$ 10,404,458	$ (483,243)	$ (2,096,861)