Consolidated Statements of Shareholders' Equity - USD ($) shares in Thousands, $ in Thousands	Total	Cumulative Effect, Period of Adoption, Adjustment	[1]	Preferred Stock	Common Stock	Additional Paid-In Capital	Retained Earnings	Retained Earnings Cumulative Effect, Period of Adoption, Adjustment	[1]	Accumulated Other Comprehensive Income (Loss)	Treasury Stock
Beginning Balance at Dec. 31, 2019	$ 2,342,176	$ (43,807)		$ 0	$ 556,110	$ 1,499,681	$ 1,079,391	$ (43,807)		$ (137)	$ (792,869)
Beginning Balance (in shares) at Dec. 31, 2019				0	164,218
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income	65,606						65,606
Other comprehensive income	51,576									51,576
Stock issued (in shares)					648
Common stock issued	3,198				$ 1,459	540					1,200
Stock-based compensation awards	3,530					3,530
Acquisition of treasury stock (in shares)					(2,908)
Acquisition of treasury stock	(39,748)										(39,748)
Common stock cash dividends	(42,030)						(42,030)
Ending Balance at Jun. 30, 2020	2,340,501			$ 0	$ 557,569	1,503,750	1,059,160			51,439	(831,417)
Ending Balance (in shares) at Jun. 30, 2020				0	161,958
Beginning Balance at Mar. 31, 2020	2,285,748			$ 0	$ 556,243	1,502,189	1,040,646			18,308	(831,638)
Beginning Balance (in shares) at Mar. 31, 2020				0	161,435
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income	39,559						39,559
Other comprehensive income	33,131									33,131
Stock issued (in shares)					523
Common stock issued	1,197				$ 1,326	(350)					221
Stock-based compensation awards	1,911					1,911
Common stock cash dividends	(21,045)						(21,045)
Ending Balance at Jun. 30, 2020	2,340,501			$ 0	$ 557,569	1,503,750	1,059,160			51,439	(831,417)
Ending Balance (in shares) at Jun. 30, 2020				0	161,958
Beginning Balance at Dec. 31, 2020	2,616,828			$ 192,878	$ 557,917	1,508,117	1,120,781			65,091	(827,956)
Beginning Balance (in shares) at Dec. 31, 2020				200	162,350
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income	138,027						138,027
Other comprehensive income	(17,890)									(17,890)
Stock issued (in shares)					638
Common stock issued	2,715				$ 1,568	1,528					(381)
Stock-based compensation awards	4,000					4,000
Preferred stock dividend	(5,153)						(5,153)
Common stock cash dividends	(45,569)						(45,569)
Ending Balance at Jun. 30, 2021	2,692,958			$ 192,878	$ 559,485	1,513,645	1,208,086			47,201	(828,337)
Ending Balance (in shares) at Jun. 30, 2021				200	162,988
Beginning Balance at Mar. 31, 2021	2,629,655			$ 192,878	$ 558,116	1,511,101	1,168,491			25,838	(826,769)
Beginning Balance (in shares) at Mar. 31, 2021				200	162,517
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income	64,964						64,964
Other comprehensive income	21,363									21,363
Stock issued (in shares)					471
Common stock issued	247				$ 1,369	446					(1,568)
Stock-based compensation awards	2,098					2,098
Preferred stock dividend	(2,562)						(2,562)
Common stock cash dividends	(22,807)						(22,807)
Ending Balance at Jun. 30, 2021	$ 2,692,958			$ 192,878	$ 559,485	$ 1,513,645	$ 1,208,086			$ 47,201	$ (828,337)
Ending Balance (in shares) at Jun. 30, 2021				200	162,988

[1] The Corporation adopted ASU 2016-13 "Financial Instruments - Credit Losses (Topic 326): Measurement of Credit Losses of Financial Instruments on January 1, 2020. See Note 1, "Basis of Presentation" to the Consolidated Financial Statements for further details.