Consolidated Statements of Changes in Stockholders' Equity (Unaudited) - USD ($) $ in Thousands		Total	Preferred Equity	Common Stock	Surplus	Retained Earnings	Retained Earnings Series C Preferred Stock	Retained Earnings Series D Preferred Stock	Retained Earnings Series E Preferred Stock	Accumulated Other Comprehensive Income (Loss)	Treasury Stock
Beginning balance at Dec. 31, 2017		$ 3,237,443	$ 159,929	$ 1,618	$ 1,338,722	$ 1,934,696				$ (62,758)	$ (134,764)
Comprehensive income
Net income		69,456				69,456
Other comprehensive income (loss)		(31,177)								(31,177)
Adoption of new accounting standards		(13,738)								(13,738)
Comprehensive income		24,541
Common stock issued
Stock-based compensation plans, net		10,691			(7,665)	20,136					(1,780)
Acquisition of Bank Mutual		481,688		134	390,258						91,296
Purchase of common stock returned to authorized but unissued		(26,480)		(11)	(26,469)
Purchase of treasury stock		(5,240)									(5,240)
Cash dividends
Common stock ($0.15 per share in 2018 and $0.17 per share in 2019)		(25,710)				(25,710)
Preferred stock(a)	[1]	(2,339)				(2,339)
Purchase of preferred stock		(78)	(76)			(2)
Stock-based compensation expense, net		3,675			3,675
Tax Act reclassification		13,654				13,654
Change in accounting principle		84				84
Other		771				771
Ending balance at Mar. 31, 2018		3,712,699	159,853	1,741	1,698,521	2,010,746				(107,673)	(50,488)
Beginning balance at Dec. 31, 2017		3,237,443	159,929	1,618	1,338,722	1,934,696				(62,758)	(134,764)
Comprehensive income
Net income		244,578
Other comprehensive income (loss)		(72,762)								(72,762)
Comprehensive income		171,816
Cash dividends
Proceeds from Issuance of Preferred Stock and Preference Stock		97,315
Change in accounting principle										(84)
Ending balance at Sep. 30, 2018		3,797,038	256,716	1,752	1,709,078	2,128,490				(135,520)	(163,478)
Cash dividends
Decrease Adjustment Options RSA and RSU					561
Increase Adjustment Options, RSA and RSU						272					289
Preferred Stock, Dividends, Per Share, Cash Paid							$ 0.3828125	$ 0.3359375
Beginning balance at Mar. 31, 2018		3,712,699	159,853	1,741	1,698,521	2,010,746				(107,673)	(50,488)
Comprehensive income
Net income		89,192				89,192
Other comprehensive income (loss)		(12,215)								(12,215)
Comprehensive income		76,977
Common stock issued
Stock-based compensation plans, net		5,456			1,455	(485)					4,486
Acquisition of Bank Mutual		6,720		3	6,717
Purchase of common stock returned to authorized but unissued		(6,595)		(3)	(6,592)
Purchase of treasury stock		(477)									(477)
Cash dividends
Common stock ($0.15 per share in 2018 and $0.17 per share in 2019)		(26,107)				(26,107)
Preferred stock(a)	[1]	(2,329)				(2,329)
Common stock warrants exercised		0		10	(10)
Purchase of preferred stock		(459)	(452)			(6)
Stock-based compensation expense, net		4,497			4,497
Other		(139)				(139)
Ending balance at Jun. 30, 2018		3,770,244	159,401	1,751	1,704,587	2,070,872				(119,888)	(46,479)
Comprehensive income
Net income		85,929				85,929
Other comprehensive income (loss)		(15,631)								(15,631)
Comprehensive income		70,298
Common stock issued
Stock-based compensation plans, net	[2]	1,246			(129)	(289)					1,664
Purchase of treasury stock		(118,663)									(118,663)
Cash dividends
Common stock ($0.15 per share in 2018 and $0.17 per share in 2019)		(25,614)				(25,614)
Preferred stock(a)	[1],[3]	(2,409)				(2,409)
Proceeds from Issuance of Preferred Stock and Preference Stock		97,315	97,315
Common stock warrants exercised		0		1	(1)
Stock-based compensation expense, net		4,620			4,620
Ending balance at Sep. 30, 2018		3,797,038	256,716	1,752	1,709,078	2,128,490				(135,520)	(163,478)
Cash dividends
Preferred Stock, Dividends, Per Share, Cash Paid									$ 0.3671875
Beginning balance at Dec. 31, 2018		3,780,888	256,716	1,752	1,712,615	2,181,414				(124,972)	(246,638)
Comprehensive income
Net income		86,686				86,686
Other comprehensive income (loss)		21,597								21,597
Comprehensive income		108,283
Common stock issued
Stock-based compensation plans, net		7,045			(32,220)						39,265
Purchase of treasury stock		(37,467)									(37,467)
Cash dividends
Common stock ($0.15 per share in 2018 and $0.17 per share in 2019)		(28,183)				(28,183)
Preferred stock(a)	[4]	(3,801)				(3,801)
Stock-based compensation expense, net		9,397			9,397
Other		(293)				(293)
Ending balance at Mar. 31, 2019		3,835,870	256,716	1,752	1,689,792	2,235,824				(103,375)	(244,840)
Beginning balance at Dec. 31, 2018		3,780,888	256,716	1,752	1,712,615	2,181,414				(124,972)	(246,638)
Comprehensive income
Net income		254,686
Other comprehensive income (loss)		88,020								88,020
Comprehensive income		342,706
Cash dividends
Proceeds from Issuance of Preferred Stock and Preference Stock		0
Ending balance at Sep. 30, 2019		3,920,855	256,716	1,752	1,713,971	2,341,158				(36,953)	(355,791)
Cash dividends
Preferred Stock, Dividends, Per Share, Cash Paid									$ 0.3671875
Beginning balance at Mar. 31, 2019		3,835,870	256,716	1,752	1,689,792	2,235,824				(103,375)	(244,840)
Comprehensive income
Net income		84,661				84,661
Other comprehensive income (loss)		44,311								44,311
Comprehensive income		128,972
Common stock issued
Stock-based compensation plans, net		827			(211)						1,038
Purchase of treasury stock		(40,433)									(40,433)
Cash dividends
Common stock ($0.15 per share in 2018 and $0.17 per share in 2019)		(27,776)				(27,776)
Preferred stock(a)	[4]	(3,801)				(3,801)
Stock-based compensation expense, net		6,134			6,134
Ending balance at Jun. 30, 2019		3,899,794	256,716	1,752	1,695,715	2,288,909				(59,063)	(284,235)
Comprehensive income
Net income		83,339				83,339
Other comprehensive income (loss)		22,111								22,111
Comprehensive income		105,450
Common stock issued
Stock-based compensation plans, net		1,198			12,561						(11,363)
Purchase of treasury stock		(60,193)									(60,193)
Cash dividends
Common stock ($0.15 per share in 2018 and $0.17 per share in 2019)		(27,289)				(27,289)
Preferred stock(a)	[4]	(3,801)				(3,801)
Stock-based compensation expense, net		5,696			5,696
Ending balance at Sep. 30, 2019		$ 3,920,855	$ 256,716	$ 1,752	$ 1,713,971	$ 2,341,158				$ (36,953)	$ (355,791)

[1] (b) Series C, $0.3828125 per share and Series D, $0.3359375 per share.

[2] (a) As previously disclosed in the Corporation's 2018 Annual Report on Form 10-K, an adjustment was made to the September 30, 2018 stockholders' equity balances related to the grant and vesting of options, restricted stock awards, and restricted stock units awarded. This adjustment decreased Surplus approximately $561,000, increased Retained Earnings approximately $272,000, and increased Treasury Stock approximately $289,000. The reclassification had no impact on earnings, expenses, or total stockholders' equity.

[3] (c) Series E, $0.3671875 per share.

[4] (a) Series C, $0.3828125 per share; Series D, $0.3359375 per share; and Series E, $0.3671875 per share.