Consolidated Statements of Changes in Stockholders' Equity (Unaudited) - USD ($) $ in Thousands	Total	Preferred Equity	Common Stock	Surplus	Retained Earnings	Accumulated Other Comprehensive Income (Loss)	Treasury Stock
Beginning balance at Dec. 31, 2016	$ 3,091,312	$ 159,929	$ 1,630	$ 1,459,498	$ 1,695,764	$ (54,679)	$ (170,830)
Comprehensive income:
Net income	114,253	0	0	0	114,253	0	0
Other comprehensive income	(1,209)	0	0	0	0	1,209	0
Comprehensive income	115,462
Common stock issued:
Stock-based compensation plans, net	20,945	0	0	1,102	(20,912)	0	40,755
Purchase of treasury stock	(8,445)	0	0	0	0	0	(8,445)
Cash dividends:
Common stock dividends ($0.12 per share in 2016 and $0.15 per share in 2017)	(36,804)	0	0	0	(36,804)	0	0
Preferred stock dividends	(4,669)	0	0	0	(4,669)	0	0
Stock-based compensation expense, net	12,667	0	0	12,667	0	0	0
Other	1,034	0	0	1,034	0	0	0
Ending balance at Jun. 30, 2017	3,191,502	159,929	1,630	1,474,301	1,747,632	(53,470)	(138,520)
Beginning balance at Dec. 31, 2017	3,237,443	159,929	1,618	1,454,188	1,819,230	(62,758)	(134,764)
Comprehensive income:
Net income	158,648	0	0	0	158,648	0	0
Other comprehensive income	57,130	0	0	0	0		0
AOCI Loss Net of ASU Adoption and Tax	(43,392)					(43,392)
New Accounting Pronouncement or Change in Accounting Principle, Effect of Adoption, Quantification	(13,738)	0	0	0	0	(13,738)	0
Comprehensive income	101,518
Common stock issued:
Stock-based compensation plans, net	16,147	0	0	2,702	(15,176)	0	28,621
Stock Issued for Bank Mutual Acquisitions	488,408	0	137	396,975	0	0	91,296
Purchase of common stock returned to authorized but unissued	(33,075)		(14)	(33,061)	0	0	0
Purchase of treasury stock	(5,717)	0	0	0	0	0	(5,717)
Cash dividends:
Common stock dividends ($0.12 per share in 2016 and $0.15 per share in 2017)	(51,817)	0	0	0	(51,817)	0	0
Preferred stock dividends	(4,668)	0	0	0	(4,668)	0	0
Preferred Stock Redemption Premium	(646)	(528)	0	0	(118)	0	0
Proceeds from Warrant Exercises	0	0	10	(10)	0	0	0
Stock-based compensation expense, net	8,172	0	0	8,172	0	0	0
Tax Act Reclassification (2018-2)	13,654	0	0	0	13,654		0
Change in Equity Securities(2016-01)	84	0	0	0	84		0
Other	742	0	0	0	742	0	0
Ending balance at Jun. 30, 2018	$ 3,770,244	$ 159,401	$ 1,751	$ 1,828,965	$ 1,920,579	$ (119,888)	$ (20,564)