Consolidated Statements of Changes in Shareholders' Equity - USD ($) $ in Thousands	Total	Preferred Stock [Member]	Common Stock [Member]	Additional Paid-in Capital [Member]	Retained Earnings [Member]	AOCI Attributable to Parent [Member]	Treasury Stock [Member]
Cumulative effect of accounting change	$ (29,252)				$ (29,252)
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest, Adjusted Balance	3,882,416	$ 144,486	$ 642	$ 983,250	2,638,282	$ 267,370	$ (151,614)
Total shareholders’ equity at beginning of period at Dec. 31, 2019	3,911,668	144,486	642	983,250	2,667,534	267,370	(151,614)
Net income	242,881				242,881
Other comprehensive income (loss)	237,775					237,775
Stock option exercises/stock unit conversions (21,968 shares QTD and 650,044 shares YTD in 2021 and 53,425 shares QTD and 196,948 shares YTD in 2020)	7,544				(11,627)		19,171
Stock compensation expense recognized in earnings	8,227			8,227
Preferred stock, redemption amount (6,000,000 shares)	(150,000)	(144,486)			(5,514)
Purchase of treasury stock (478 shares QTD and 12,103 shares YTD in 2021 and 400 shares QTD and 182,225 shares YTD in 2020)	(14,000)						(14,000)
Treasury stock issued to the 401(k) stock purchase plan (18,555 shares YTD in 2021 and 58,900 shares QTD and 97,843 shares YTD in 2020)	6,961				(2,563)		9,524
Cash dividends – preferred stock (approximately $11.13 per share which is equivalent to approximately $0.28 per depository share QTD and $36.59 per share which is equivalent to approximately $0.91 per depository share YTD in 2021 and $0.34 per share YTD in 2020)	(2,016)				(2,016)
Cash dividends – common stock ($0.75 per share QTD and $2.19 per share YTD in 2021 and $0.71 per share QTD and $2.13 per share YTD in 2020)	(134,762)				(134,762)
Total shareholders’ equity at end of period at Sep. 30, 2020	$ 4,085,026	0	642	991,477	2,724,681	505,145	(136,919)
Purchase of treasury stock (478 shares QTD and 12,103 shares during 2021 and 400 shares QTD and 182,225 shares during 2020)	(182,225)
Total shareholders’ equity at beginning of period at Jun. 30, 2020	$ 4,008,801	0	642	989,034	2,678,686	488,264	(147,825)
Net income	95,056				95,056
Other comprehensive income (loss)	16,881					16,881
Stock option exercises/stock unit conversions (21,968 shares QTD and 650,044 shares YTD in 2021 and 53,425 shares QTD and 196,948 shares YTD in 2020)	2,698				(2,502)		5,200
Stock compensation expense recognized in earnings	2,443			2,443
Purchase of treasury stock (478 shares QTD and 12,103 shares YTD in 2021 and 400 shares QTD and 182,225 shares YTD in 2020)	(27)						(27)
Treasury stock issued to the 401(k) stock purchase plan (18,555 shares YTD in 2021 and 58,900 shares QTD and 97,843 shares YTD in 2020)	4,131				(1,602)		5,733
Cash dividends – common stock ($0.75 per share QTD and $2.19 per share YTD in 2021 and $0.71 per share QTD and $2.13 per share YTD in 2020)	(44,957)				(44,957)
Total shareholders’ equity at end of period at Sep. 30, 2020	$ 4,085,026	0	642	991,477	2,724,681	505,145	(136,919)
Purchase of treasury stock (478 shares QTD and 12,103 shares during 2021 and 400 shares QTD and 182,225 shares during 2020)	(400)
Total shareholders’ equity at beginning of period at Dec. 31, 2020	$ 4,293,016	145,452	642	997,168	2,750,723	512,970	(113,939)
Net income	342,058				342,058
Other comprehensive income (loss)	(162,687)					(162,687)
Stock option exercises/stock unit conversions (21,968 shares QTD and 650,044 shares YTD in 2021 and 53,425 shares QTD and 196,948 shares YTD in 2020)	37,810				(26,652)		64,462
Stock compensation expense recognized in earnings	7,756			7,756
Purchase of treasury stock (478 shares QTD and 12,103 shares YTD in 2021 and 400 shares QTD and 182,225 shares YTD in 2020)	(1,342)						(1,342)
Treasury stock issued to the 401(k) stock purchase plan (18,555 shares YTD in 2021 and 58,900 shares QTD and 97,843 shares YTD in 2020)	1,749				(57)		1,806
Cash dividends – preferred stock (approximately $11.13 per share which is equivalent to approximately $0.28 per depository share QTD and $36.59 per share which is equivalent to approximately $0.91 per depository share YTD in 2021 and $0.34 per share YTD in 2020)	(5,488)				(5,488)
Cash dividends – common stock ($0.75 per share QTD and $2.19 per share YTD in 2021 and $0.71 per share QTD and $2.13 per share YTD in 2020)	(140,510)				(140,510)
Total shareholders’ equity at end of period at Sep. 30, 2021	$ 4,372,362	145,452	642	1,004,924	2,920,074	350,283	(49,013)
Purchase of treasury stock (478 shares QTD and 12,103 shares during 2021 and 400 shares QTD and 182,225 shares during 2020)	(12,103)
Total shareholders’ equity at beginning of period at Jun. 30, 2021	$ 4,373,817	145,452	642	1,002,939	2,862,966	412,990	(51,172)
Net income	107,975				107,975
Other comprehensive income (loss)	(62,707)					(62,707)
Stock option exercises/stock unit conversions (21,968 shares QTD and 650,044 shares YTD in 2021 and 53,425 shares QTD and 196,948 shares YTD in 2020)	1,128				(1,085)		2,213
Stock compensation expense recognized in earnings	1,985			1,985
Purchase of treasury stock (478 shares QTD and 12,103 shares YTD in 2021 and 400 shares QTD and 182,225 shares YTD in 2020)	(54)						(54)
Cash dividends – preferred stock (approximately $11.13 per share which is equivalent to approximately $0.28 per depository share QTD and $36.59 per share which is equivalent to approximately $0.91 per depository share YTD in 2021 and $0.34 per share YTD in 2020)	(1,668)				(1,668)
Cash dividends – common stock ($0.75 per share QTD and $2.19 per share YTD in 2021 and $0.71 per share QTD and $2.13 per share YTD in 2020)	(48,114)				(48,114)
Total shareholders’ equity at end of period at Sep. 30, 2021	$ 4,372,362	$ 145,452	$ 642	$ 1,004,924	$ 2,920,074	$ 350,283	$ (49,013)
Purchase of treasury stock (478 shares QTD and 12,103 shares during 2021 and 400 shares QTD and 182,225 shares during 2020)	(478)