Consolidated Statements Of Changes In Equity - USD ($) $ in Thousands	Total	Preferred Stock [Member]	Common Stock [Member]	Capital Surplus [Member]	Retained Earnings [Member]	Treasury Stock [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Non-Controlling Interest [Member]
Balance at Dec. 31, 2014	$ 2,334,246	$ 144,784	$ 484,155	$ 1,229,075	$ 426,648	$ (16,562)	$ 62,093	$ 4,053
Net income	62,014				61,055			959
Other comprehensive income (loss)	29,624						29,624
Distributions to non-controlling interest	(219)							(219)
Purchase of treasury stock	(1,718)					(1,718)
Issuance of stock under purchase and equity compensation plans	1,865			(9,547)		11,412
Net tax benefit related to equity compensation plans	857			857
Stock-based compensation	2,740			2,740
Cash dividends per share, Common Stock, Cash	(21,752)				(21,752)
Dividends per share, Preferred Stock, Cash	(2,250)				(2,250)
Balance at Mar. 31, 2015	2,405,407	144,784	$ 484,155	1,223,125	463,701	(6,868)	91,717	4,793
Balance at Dec. 31, 2015	2,367,418	144,784	489,862	1,337,677	383,313	(26,116)	32,470	5,428
Net income	65,522				65,374			148
Other comprehensive income (loss)	70,459						70,459
Distributions to non-controlling interest	(322)							(322)
Purchase of treasury stock	(36,432)					(36,432)
Issuance of stock under purchase and equity compensation plans	0			(9,895)		9,895
Net tax benefit related to equity compensation plans	1,236			1,236
Stock-based compensation	3,411			3,411
Cash dividends per share, Common Stock, Cash	(21,760)				(21,760)
Dividends per share, Preferred Stock, Cash	(2,250)				(2,250)
Balance at Mar. 31, 2016	$ 2,447,282	$ 144,784	$ 489,862	$ 1,332,429	$ 424,677	$ (52,653)	$ 102,929	$ 5,254