Consolidated Statement of Changes in Shareholders' Equity - USD ($) $ in Thousands	Total	Preferred Stock [Member]	Common Stock [Member]	Additional Paid-In Capital [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Income (Loss), Net of Tax [Member]	Treasury Stock [Member]
Balance at Dec. 31, 2015	$ 2,890,343	$ 144,486	$ 637	$ 897,350	$ 1,845,188	$ 113,863	$ (111,181)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	304,261				304,261
Other comprehensive loss, net of tax	(138,486)					(138,486)
Proceeds from stock option exercises/stock unit conversions	78,866			(2,417)	(20,915)		102,198
Stock-based compensation expense recognized in earnings	11,799			11,799
Purchase of treasury stock	(1,290)						(1,290)
Cash dividends paid on preferred stock	(8,063)				(8,063)
Cash dividends – common stock	(134,902)				(134,902)
Balance at Dec. 31, 2016	3,002,528	144,486	637	906,732	1,985,569	(24,623)	(10,273)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	364,149				364,149
Other comprehensive loss, net of tax	104,135					104,135
Proceeds from stock option exercises/stock unit conversions	67,746		5	33,616	(10,414)		44,539
Stock-based compensation expense recognized in earnings	13,013			13,013
Purchase of treasury stock	(101,473)						(101,473)
Cash dividends paid on preferred stock	(8,063)				(8,063)
Cash dividends – common stock	(144,172)				(144,172)
Balance at Dec. 31, 2017	3,297,863	144,486	642	953,361	2,187,069	79,512	(67,207)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative Effect of New Accounting Principle in Period of Adoption	(2,285)				(2,285)
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest, Adjusted Balance	3,295,578	144,486	642	953,361	2,184,784	79,512	(67,207)
Net income	454,918				454,918
Other comprehensive loss, net of tax	(152,647)					(152,647)
Reclassification of certain income tax effects related to U.S. statutory federal income tax rate under the Tax Cuts and Jobs Act					(9,535)	9,535
Proceeds from stock option exercises/stock unit conversions	31,647				(16,653)		48,300
Stock-based compensation expense recognized in earnings	13,943			13,943
Purchase of treasury stock	(101,010)						(101,010)
Cash dividends paid on preferred stock	(8,063)				(8,063)
Cash dividends – common stock	(165,449)				(165,449)
Balance at Dec. 31, 2018	$ 3,368,917	$ 144,486	$ 642	$ 967,304	$ 2,440,002	$ (63,600)	$ (119,917)