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	$ (14,672)				$ (14,672)
Total shareholders' equity at beginning of period, as adjusted	3,354,245	$ 144,486	$ 642	$ 967,304	2,425,330	$ (63,600)	$ (119,917)
Total shareholders’ equity at beginning of period at Dec. 31, 2018	3,368,917	144,486	642	967,304	2,440,002	(63,600)	(119,917)
Net income	228,082				228,082
Other comprehensive income (loss)	283,038					283,038
Stock option exercises/stock unit conversions (77,308 shares QTD and 143,523 shares YTD in 2020 and 53,035 shares QTD and 153,900 shares YTD in 2019)	7,841				(5,718)		13,559
Stock compensation expense recognized in earnings	8,018			8,018
Purchase of treasury stock (181,825 shares YTD in 2020 and 496,307 shares QTD and 501,658 shares YTD in 2019)	(50,519)						(50,519)
Treasury stock issued to the 401(k) stock purchase plan (38,943 shares)	0
Cash dividends – preferred stock (approximately $0.34 per share YTD in 2020 and $0.33 QTD and $0.67 YTD in 2019)	(4,031)				(4,031)
Cash dividends – common stock ($0.71 per share QTD and $1.42 per share YTD in 2020 and $0.71 per share and $1.38 per share YTD in 2019)	(87,428)				(87,428)
Total shareholders’ equity at end of period at Jun. 30, 2019	$ 3,739,246	144,486	642	975,322	2,556,235	219,438	(156,877)
Stock option exercises/stock unit conversions (shares)	153,900
Treasury Stock, Shares, Acquired	501,658
Approximate cash dividends declared on preferred stock, per share	$ 0.67
Cash dividends declared on common stock, per share	$ 1.38
Total shareholders’ equity at beginning of period at Mar. 31, 2019	$ 3,591,517	144,486	642	970,958	2,493,207	93,774	(111,550)
Net income	111,586				111,586
Other comprehensive income (loss)	125,664					125,664
Stock option exercises/stock unit conversions (77,308 shares QTD and 143,523 shares YTD in 2020 and 53,035 shares QTD and 153,900 shares YTD in 2019)	2,956				(1,717)		4,673
Stock compensation expense recognized in earnings	4,364			4,364
Purchase of treasury stock (181,825 shares YTD in 2020 and 496,307 shares QTD and 501,658 shares YTD in 2019)	(50,000)						(50,000)
Cash dividends – preferred stock (approximately $0.34 per share YTD in 2020 and $0.33 QTD and $0.67 YTD in 2019)	(2,015)				(2,015)
Cash dividends – common stock ($0.71 per share QTD and $1.42 per share YTD in 2020 and $0.71 per share and $1.38 per share YTD in 2019)	(44,826)				(44,826)
Total shareholders’ equity at end of period at Jun. 30, 2019	$ 3,739,246	144,486	642	975,322	2,556,235	219,438	(156,877)
Stock option exercises/stock unit conversions (shares)	53,035
Treasury Stock, Shares, Acquired	496,307
Approximate cash dividends declared on preferred stock, per share	$ 0.33
Cash dividends declared on common stock, per share	$ 0.71
Cumulative effect of accounting change	$ (29,252)				(29,252)
Total shareholders' equity at beginning of period, as adjusted	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)
Total shareholders’ equity at end of period at Mar. 31, 2020	3,826,666	0	642	985,762	2,635,588	363,815	(159,141)
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	147,825				147,825
Other comprehensive income (loss)	220,894					220,894
Stock option exercises/stock unit conversions (77,308 shares QTD and 143,523 shares YTD in 2020 and 53,035 shares QTD and 153,900 shares YTD in 2019)	4,846				(9,125)		13,971
Stock compensation expense recognized in earnings	5,784			5,784
Preferred stock, redemption amount (6,000,000 shares)	(150,000)	(144,486)			(5,514)
Purchase of treasury stock (181,825 shares YTD in 2020 and 496,307 shares QTD and 501,658 shares YTD in 2019)	(13,973)						(13,973)
Treasury stock issued to the 401(k) stock purchase plan (38,943 shares)	2,830				(961)		3,791
Cash dividends – preferred stock (approximately $0.34 per share YTD in 2020 and $0.33 QTD and $0.67 YTD in 2019)	(2,016)				(2,016)
Cash dividends – common stock ($0.71 per share QTD and $1.42 per share YTD in 2020 and $0.71 per share and $1.38 per share YTD in 2019)	(89,805)				(89,805)
Total shareholders’ equity at end of period at Jun. 30, 2020	$ 4,008,801	0	642	989,034	2,678,686	488,264	(147,825)
Stock option exercises/stock unit conversions (shares)	143,523
Redemption of preferred stock (6,000,000 shares)	6,000,000
Treasury Stock, Shares, Acquired	181,825
Treasury stock issued to the 401(k) stock purchase plan (38,943 shares)	38,943
Approximate cash dividends declared on preferred stock, per share	$ 0.34
Cash dividends declared on common stock, per share	$ 1.42
Total shareholders’ equity at beginning of period at Mar. 31, 2020	$ 3,826,666	0	642	985,762	2,635,588	363,815	(159,141)
Net income	93,072				93,072
Other comprehensive income (loss)	124,449					124,449
Stock option exercises/stock unit conversions (77,308 shares QTD and 143,523 shares YTD in 2020 and 53,035 shares QTD and 153,900 shares YTD in 2019)	3,383				(4,142)		7,525
Stock compensation expense recognized in earnings	3,272			3,272
Treasury stock issued to the 401(k) stock purchase plan (38,943 shares)	2,830				(961)		3,791
Cash dividends – common stock ($0.71 per share QTD and $1.42 per share YTD in 2020 and $0.71 per share and $1.38 per share YTD in 2019)	(44,871)				(44,871)
Total shareholders’ equity at end of period at Jun. 30, 2020	$ 4,008,801	$ 0	$ 642	$ 989,034	$ 2,678,686	$ 488,264	$ (147,825)
Stock option exercises/stock unit conversions (shares)	77,308
Treasury stock issued to the 401(k) stock purchase plan (38,943 shares)	38,943
Cash dividends declared on common stock, per share	$ 0.71