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	116,496				116,496
Other comprehensive income (loss)	157,374					157,374
Stock option exercises/stock unit conversions (66,215 shares YTD in 2020 and 100,865 shares YTD in 2019)	4,885				(4,001)		8,886
Stock compensation expense recognized in earnings	3,654			3,654
Purchase of treasury stock (181,825 shares YTD in 2020 and 5,351 shares YTD in 2019)	(519)						(519)
Cash dividends – preferred stock (approximately $0.34 per share YTD in both 2020 and 2019)	(2,016)				(2,016)
Cash dividends – common stock ($0.71 per share YTD in 2020 and $0.67 per share YTD in 2019)	(42,602)				(42,602)
Total shareholders’ equity at end of period at Mar. 31, 2019	3,591,517	144,486	642	970,958	2,493,207	93,774	(111,550)
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)
Net income	54,753				54,753
Other comprehensive income (loss)	96,445					96,445
Stock option exercises/stock unit conversions (66,215 shares YTD in 2020 and 100,865 shares YTD in 2019)	1,463				(4,983)		6,446
Stock compensation expense recognized in earnings	2,512			2,512
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 5,351 shares YTD in 2019)	(13,973)						(13,973)
Cash dividends – preferred stock (approximately $0.34 per share YTD in both 2020 and 2019)	(2,016)				(2,016)
Cash dividends – common stock ($0.71 per share YTD in 2020 and $0.67 per share YTD in 2019)	(44,934)				(44,934)
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)