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)
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest, Adjusted Balance	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	339,918				339,918
Other comprehensive income (loss)	368,983					368,983
Stock option exercises/stock unit conversions (53,425 shares QTD and 196,948 shares YTD in 2020 and 101,284 shares QTD and 255,184 shares YTD in 2019)	13,506				(9,569)		23,075
Stock compensation expense recognized in earnings	10,693			10,693
Purchase of treasury stock (400 shares QTD and 182,225 shares YTD in 2020 and 202,724 shares QTD and 704,382 shares YTD in 2019)	(67,709)						(67,709)
Treasury stock issued to the 401(k) stock purchase plan (58,900 shares QTD and 97,843 YTD in 2020)	0
Cash dividends – preferred stock (approximately $0.34 per share YTD in 2020 and $0.34 QTD and $1.01 YTD in 2019)	(6,047)				(6,047)
Cash dividends – common stock ($0.71 per share QTD and $2.13 per share YTD in 2020 and $0.71 per share and $2.09 per share YTD in 2019)	(132,132)				(132,132)
Total shareholders’ equity at end of period at Sep. 30, 2019	3,881,457	144,486	642	977,997	2,617,500	305,383	(164,551)
Total shareholders’ equity at beginning of period at Jun. 30, 2019	3,739,246	144,486	642	975,322	2,556,235	219,438	(156,877)
Net income	111,836				111,836
Other comprehensive income (loss)	85,945					85,945
Stock option exercises/stock unit conversions (53,425 shares QTD and 196,948 shares YTD in 2020 and 101,284 shares QTD and 255,184 shares YTD in 2019)	5,665				(3,851)		9,516
Stock compensation expense recognized in earnings	2,675			2,675
Purchase of treasury stock (400 shares QTD and 182,225 shares YTD in 2020 and 202,724 shares QTD and 704,382 shares YTD in 2019)	(17,190)						(17,190)
Cash dividends – preferred stock (approximately $0.34 per share YTD in 2020 and $0.34 QTD and $1.01 YTD in 2019)	(2,016)				(2,016)
Cash dividends – common stock ($0.71 per share QTD and $2.13 per share YTD in 2020 and $0.71 per share and $2.09 per share YTD in 2019)	(44,704)				(44,704)
Total shareholders’ equity at end of period at Sep. 30, 2019	3,881,457	144,486	642	977,997	2,617,500	305,383	(164,551)
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 (53,425 shares QTD and 196,948 shares YTD in 2020 and 101,284 shares QTD and 255,184 shares YTD in 2019)	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 (400 shares QTD and 182,225 shares YTD in 2020 and 202,724 shares QTD and 704,382 shares YTD in 2019)	(14,000)						(14,000)
Treasury stock issued to the 401(k) stock purchase plan (58,900 shares QTD and 97,843 YTD in 2020)	6,961				(2,563)		9,524
Cash dividends – preferred stock (approximately $0.34 per share YTD in 2020 and $0.34 QTD and $1.01 YTD in 2019)	(2,016)				(2,016)
Cash dividends – common stock ($0.71 per share QTD and $2.13 per share YTD in 2020 and $0.71 per share and $2.09 per share YTD in 2019)	(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)
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 (53,425 shares QTD and 196,948 shares YTD in 2020 and 101,284 shares QTD and 255,184 shares YTD in 2019)	2,698				(2,502)		5,200
Stock compensation expense recognized in earnings	2,443			2,443
Purchase of treasury stock (400 shares QTD and 182,225 shares YTD in 2020 and 202,724 shares QTD and 704,382 shares YTD in 2019)	(27)						(27)
Treasury stock issued to the 401(k) stock purchase plan (58,900 shares QTD and 97,843 YTD in 2020)	4,131				(1,602)		5,733
Cash dividends – common stock ($0.71 per share QTD and $2.13 per share YTD in 2020 and $0.71 per share and $2.09 per share YTD in 2019)	(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)