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	56,270	0	0	0	56,270	0	0
Other comprehensive income	(1,665)	0	0	0	0	1,665	0
Comprehensive income	54,605
Common stock issued:
Stock-based compensation plans, net	17,940	0	0	868	(21,822)	0	38,894
Purchase of treasury stock	(7,743)	0	0	0	0	0	(7,743)
Cash dividends:
Common stock dividends ($0.12 per share in 2016 and $0.15 per share in 2017)	(18,368)	0	0	0	(18,368)	0	0
Preferred stock dividends	(2,330)	0	0	0	(2,330)	0	0
Stock-based compensation expense, net	8,344	0	0	8,344	0	0	0
Other	1,034	0	0	1,034	0	0	0
Ending balance at Mar. 31, 2017	3,144,794	159,929	1,630	1,469,744	1,709,514	(56,344)	(139,679)
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	69,456	0	0	0	69,456	0	0
Other comprehensive income	(44,915)	0	0	0	0		0
AOCI Loss Net of ASU Adoption and Tax	(31,177)					(31,177)
New Accounting Pronouncement or Change in Accounting Principle, Effect of Adoption, Quantification	(13,738)	0	0	0	0	(13,738)	0
Comprehensive income	24,541
Common stock issued:
Stock-based compensation plans, net	10,691	0	0	2,148	(16,076)	0	24,619
Stock Issued for Bank Mutual Acquisitions	481,688	0	134	390,258	0	0	91,296
Purchase of common stock returned to authorized but unissued	(26,480)		(11)	(26,469)	0	0	0
Purchase of treasury stock	(5,240)	0	0	0	0	0	(5,240)
Cash dividends:
Common stock dividends ($0.12 per share in 2016 and $0.15 per share in 2017)	(25,710)	0	0	0	(25,710)	0	0
Preferred stock dividends	(2,339)	0	0	0	(2,339)	0	0
Preferred Stock Redemption Premium	(78)	(76)	0	0	(2)	0	0
Stock-based compensation expense, net	3,675	0	0	3,675	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	771	0	0	0	771	0	0
Ending balance at Mar. 31, 2018	$ 3,712,699	$ 159,853	$ 1,741	$ 1,823,800	$ 1,859,068	$ (107,673)	$ (24,089)