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	217,821				217,821
Other comprehensive income (loss)	(152,366)					(152,366)
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 (53,035 shares QTD and 153,900 shares YTD in 2019 and 110,489 shares QTD and 428,599 shares YTD in 2018)	25,448				(12,312)		37,760
Stock compensation expense recognized in earnings	6,760			6,760
Purchase of treasury stock (496,307 shares QTD and 501,658 shares YTD in 2019 and 601 shares both QTD and YTD in 2018)	(70)						(70)
Cash dividends – preferred stock (approximately $0.33 per share QTD and $0.67 per share YTD in both 2019 and in 2018)	(4,031)				(4,031)
Cash dividends – common stock ($0.71 per share QTD and $1.38 per share YTD in 2019 and $0.67 per share QTD and $1.24 per share YTD in 2018)	(79,628)				(79,628)
Total shareholders’ equity at end of period at Jun. 30, 2018	3,309,512	144,486	642	960,121	2,297,099	(63,319)	(29,517)
Total shareholders’ equity at beginning of period at Mar. 31, 2018	3,243,430	144,486	642	956,536	2,234,301	(53,354)	(39,181)
Net income	111,341				111,341
Other comprehensive income (loss)	(9,965)					(9,965)
Stock option exercises/stock unit conversions (53,035 shares QTD and 153,900 shares YTD in 2019 and 110,489 shares QTD and 428,599 shares YTD in 2018)	6,283				(3,451)		9,734
Stock compensation expense recognized in earnings	3,585			3,585
Purchase of treasury stock (496,307 shares QTD and 501,658 shares YTD in 2019 and 601 shares both QTD and YTD in 2018)	(70)						(70)
Cash dividends – preferred stock (approximately $0.33 per share QTD and $0.67 per share YTD in both 2019 and in 2018)	(2,015)				(2,015)
Cash dividends – common stock ($0.71 per share QTD and $1.38 per share YTD in 2019 and $0.67 per share QTD and $1.24 per share YTD in 2018)	(43,077)				(43,077)
Total shareholders’ equity at end of period at Jun. 30, 2018	3,309,512	144,486	642	960,121	2,297,099	(63,319)	(29,517)
Cumulative effect of new accounting principle in period of adoption	(12,611)				(12,611)
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)
Total shareholders' equity at beginning of period, as adjusted at Dec. 31, 2018	3,356,306	144,486	642	967,304	2,427,391	(63,600)	(119,917)
Net income	228,082				228,082
Other comprehensive income (loss)	283,038					283,038
Stock option exercises/stock unit conversions (53,035 shares QTD and 153,900 shares YTD in 2019 and 110,489 shares QTD and 428,599 shares YTD in 2018)	7,841				(5,718)		13,559
Stock compensation expense recognized in earnings	8,018			8,018
Purchase of treasury stock (496,307 shares QTD and 501,658 shares YTD in 2019 and 601 shares both QTD and YTD in 2018)	(50,519)						(50,519)
Cash dividends – preferred stock (approximately $0.33 per share QTD and $0.67 per share YTD in both 2019 and in 2018)	(4,031)				(4,031)
Cash dividends – common stock ($0.71 per share QTD and $1.38 per share YTD in 2019 and $0.67 per share QTD and $1.24 per share YTD in 2018)	(87,428)				(87,428)
Total shareholders’ equity at end of period at Jun. 30, 2019	3,741,307	144,486	642	975,322	2,558,296	219,438	(156,877)
Total shareholders’ equity at beginning of period at Mar. 31, 2019	3,593,578	144,486	642	970,958	2,495,268	93,774	(111,550)
Net income	111,586				111,586
Other comprehensive income (loss)	125,664					125,664
Stock option exercises/stock unit conversions (53,035 shares QTD and 153,900 shares YTD in 2019 and 110,489 shares QTD and 428,599 shares YTD in 2018)	2,956				(1,717)		4,673
Stock compensation expense recognized in earnings	4,364			4,364
Purchase of treasury stock (496,307 shares QTD and 501,658 shares YTD in 2019 and 601 shares both QTD and YTD in 2018)	(50,000)						(50,000)
Cash dividends – preferred stock (approximately $0.33 per share QTD and $0.67 per share YTD in both 2019 and in 2018)	(2,015)				(2,015)
Cash dividends – common stock ($0.71 per share QTD and $1.38 per share YTD in 2019 and $0.67 per share QTD and $1.24 per share YTD in 2018)	(44,826)				(44,826)
Total shareholders’ equity at end of period at Jun. 30, 2019	$ 3,741,307	$ 144,486	$ 642	$ 975,322	$ 2,558,296	$ 219,438	$ (156,877)