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 new accounting principle in period of adoption	$ (2,285)				$ (2,285)
Total shareholders’ equity at beginning of period at Dec. 31, 2017	3,297,863	$ 144,486	$ 642	$ 953,361	2,187,069	$ 79,512	$ (67,207)
Total shareholders' equity at beginning of period, as adjusted at Dec. 31, 2017	3,295,578	144,486	642	953,361	2,184,784	79,512	(67,207)
Net income	335,665				335,665
Other comprehensive income (loss)	(230,282)					(230,282)
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
Stock option exercises/stock unit conversions (101,284 shares QTD and 255,184 shares YTD in 2019 and 19,232 shares QTD and 447,831 shares YTD in 2018)	26,567				(12,887)		39,454
Stock compensation expense recognized in earnings	9,556			9,556
Purchase of treasury stock (202,724 shares QTD and 704,382 shares YTD in 2019 and 0 shares QTD and 601 shares YTD in 2018)	(70)						(70)
Cash dividends – preferred stock (approximately $0.34 per share QTD and $1.01 per share YTD in both 2019 and in 2018)	(6,047)				(6,047)
Cash dividends – common stock ($0.71 per share QTD and $2.09 per share YTD in 2019 and $0.67 per share QTD and $1.91 per share YTD in 2018)	(122,721)				(122,721)
Total shareholders’ equity at end of period at Sep. 30, 2018	3,308,246	144,486	642	962,917	2,369,259	(141,235)	(27,823)
Total shareholders’ equity at beginning of period at Jun. 30, 2018	3,309,512	144,486	642	960,121	2,297,099	(63,319)	(29,517)
Net income	117,844				117,844
Other comprehensive income (loss)	(77,916)					(77,916)
Stock option exercises/stock unit conversions (101,284 shares QTD and 255,184 shares YTD in 2019 and 19,232 shares QTD and 447,831 shares YTD in 2018)	1,119				(575)		1,694
Stock compensation expense recognized in earnings	2,796			2,796
Cash dividends – preferred stock (approximately $0.34 per share QTD and $1.01 per share YTD in both 2019 and in 2018)	(2,016)				(2,016)
Cash dividends – common stock ($0.71 per share QTD and $2.09 per share YTD in 2019 and $0.67 per share QTD and $1.91 per share YTD in 2018)	(43,093)				(43,093)
Total shareholders’ equity at end of period at Sep. 30, 2018	3,308,246	144,486	642	962,917	2,369,259	(141,235)	(27,823)
Total shareholders’ equity at end of period at Dec. 31, 2018	3,368,917	144,486	642	967,304	2,440,002	(63,600)	(119,917)
Cumulative effect of new accounting principle in period of adoption	(14,672)				(14,672)
Total shareholders' equity at beginning of period, as adjusted at Dec. 31, 2018	3,354,245	144,486	642	967,304	2,425,330	(63,600)	(119,917)
Net income	339,918				339,918
Other comprehensive income (loss)	368,983					368,983
Stock option exercises/stock unit conversions (101,284 shares QTD and 255,184 shares YTD in 2019 and 19,232 shares QTD and 447,831 shares YTD in 2018)	13,506				(9,569)		23,075
Stock compensation expense recognized in earnings	10,693			10,693
Purchase of treasury stock (202,724 shares QTD and 704,382 shares YTD in 2019 and 0 shares QTD and 601 shares YTD in 2018)	(67,709)						(67,709)
Cash dividends – preferred stock (approximately $0.34 per share QTD and $1.01 per share YTD in both 2019 and in 2018)	(6,047)				(6,047)
Cash dividends – common stock ($0.71 per share QTD and $2.09 per share YTD in 2019 and $0.67 per share QTD and $1.91 per share YTD in 2018)	(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 (101,284 shares QTD and 255,184 shares YTD in 2019 and 19,232 shares QTD and 447,831 shares YTD in 2018)	5,665				(3,851)		9,516
Stock compensation expense recognized in earnings	2,675			2,675
Purchase of treasury stock (202,724 shares QTD and 704,382 shares YTD in 2019 and 0 shares QTD and 601 shares YTD in 2018)	(17,190)						(17,190)
Cash dividends – preferred stock (approximately $0.34 per share QTD and $1.01 per share YTD in both 2019 and in 2018)	(2,016)				(2,016)
Cash dividends – common stock ($0.71 per share QTD and $2.09 per share YTD in 2019 and $0.67 per share QTD and $1.91 per share YTD in 2018)	(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)