Consolidated Statements Of Changes In Equity - USD ($) $ in Thousands	Total	Preferred Stock [Member]	Common Stock	Capital Surplus	Retained Earnings	Treasury Stock	Accumulated Other Comprehensive Income (Loss)	Non-Controlling Interest
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	266,975				263,730			3,245
Other comprehensive income	(29,623)						(29,623)
Distributions to non-controlling interest	(1,870)							(1,870)
Purchase of treasury stock	(23,176)					(23,176)
Accelerated share repurchase forward contract	(100,000)			60,000		(160,000)
Cash dividends paid on common stock	(84,961)				(84,961)
Cash dividends paid on preferred stock	(9,000)				(9,000)
Net tax benefit related to equity compensation plans	2,132			2,132
Stock-based compensation	10,147			10,147
Issuance under stock purchase and equity compensation plans, net	2,888			(16,615)		19,503
5% stock dividend, net	(340)		5,707	52,938	(213,104)	154,119
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	276,854				275,391			1,463
Other comprehensive income	(21,495)						(21,495)
Distributions to non-controlling interest	(1,542)							(1,542)
Purchase of treasury stock	(39,381)					(39,381)
Cash dividends paid on common stock	(87,070)				(87,070)
Cash dividends paid on preferred stock	(9,000)				(9,000)
Net tax benefit related to equity compensation plans	3,390			3,390
Stock-based compensation	11,525			11,525
Issuance under stock purchase and equity compensation plans, net	911			(15,810)		16,721
5% stock dividend, net	(478)		20,153	215,672	(269,785)	33,482
Balance at Dec. 31, 2016	2,501,132		510,015	1,552,454	292,849	(15,294)	10,975	5,349
Adoption for ASU 2016-09	1,297			3,441	(2,144)
Net income	319,900				319,383			517
Other comprehensive income	3,133						3,133
Distributions to non-controlling interest	(1,293)							(1,293)
Sale of non-controlling interest in subsidiary	1			2,950				(2,949)
Purchase of treasury stock	(17,771)					(17,771)
Cash dividends paid on common stock	(91,619)				(91,619)
Cash dividends paid on preferred stock	(9,000)				(9,000)
Stock-based compensation	12,105			12,105
Issuance under stock purchase and equity compensation plans, net	858			(17,734)		18,592
5% stock dividend, net	(559)		25,392	262,144	(288,095)
Balance at Dec. 31, 2017	$ 2,718,184	$ 144,784	$ 535,407	$ 1,815,360	$ 221,374	$ (14,473)	$ 14,108	$ 1,624