Consolidated Statement of Changes in Shareholders' Equity (Unaudited) - USD ($) $ in Thousands	Total	Preferred Stock [Member]	Common Stock [Member]	Common Stock [Member] Series A Warrants [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]
Beginning balance at Dec. 31, 2014	$ 12,335,896	$ 1,231,500	$ 66,157		$ 2,608	$ 3,409,506		$ 7,807,119	$ (180,994)
Total comprehensive income	270,116							241,613	28,503
Preferred stock cash dividends	(20,318)							(20,318)
Exercise of stock warrants into common stock				$ 1			$ (1)
Stock-based compensation plans:
Compensation expense, net	5,572		147			5,425
Exercises of stock options, net	19,479		101			19,378
Stock purchase plan	10,346		45			10,301
Directors' stock plan	425		2			423
Deferred compensation plans, net, including dividend equivalents	(51)		2		(298)	270		(25)
Other	405					405
Common stock cash dividends - $.70 per share	(93,569)							(93,569)
Ending balance at Mar. 31, 2015	12,528,301	1,231,500	66,455		2,310	3,445,707		7,934,820	(152,491)
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 - $.70 per share	(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)