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, 2015	$ 16,173,289	$ 1,231,500	$ 79,782	$ 2,364	$ 6,680,768		$ 8,430,502	$ (251,627)
Total comprehensive income	399,966						298,528	101,438
Preferred stock cash dividends	(20,318)						(20,318)
Purchases of treasury stock	(100,000)								$ (100,000)
Stock-based compensation plans:
Compensation expense, net	(55)		178		(978)				745
Exercises of stock options, net	2,618		18		2,335				265
Stock purchase plan	10,594				275				10,319
Directors' stock plan	473		2		471
Deferred compensation plans, net, including dividend equivalents	29		2	(184)	234		(23)
Other	394				394
Common stock cash dividends	(111,937)						(111,937)
Ending balance at Mar. 31, 2016	16,355,053	1,231,500	79,982	2,180	6,683,499		8,596,752	(150,189)	(88,671)
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)