Consolidated Statements of Changes in Stockholders' Equity (Unaudited) - USD ($) $ in Thousands	Total	Preferred Equity	Common Stock	Surplus		Retained Earnings		AOCI Allocated to Parent [Member]	AOCI Attributable to Parent [Member]	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	0	0	0		69,456			0	0
Other Comprehensive Income, Other, Net of Tax	(31,177)	0	0	0		0			(31,177)	0
Other comprehensive income	(44,915)								(44,915)
Adoption of new accounting standards	(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	(7,665)	[1]	20,136	[1]		0	(1,780)	[1]
Acquisitions	481,688	0	134	390,258		0			0	91,296
Purchase of common stock returned to authorized but unissued	(26,480)	0	(11)	(26,469)		0			0	0
Purchase of treasury stock	(5,240)	0	0	0		0			0	(5,240)
Cash dividends:
Common stock ($0.15 per share in 2018 and $0.17 per share in 2019)	(25,710)	0	0	0		(25,710)			0	0
Preferred stock	(2,339)	0	0	0		(2,339)			0	0
Purchase of preferred stock	(78)	(76)	0	0		(2)			0	0
Stock-based compensation expense, net	3,675	0	0	3,675		0			0	0
Tax Act Reclassification	13,654	0	0	0		13,654			0	0
Change in accounting principle	84	0	0	0		84		$ 0	(84)	0
Other	771	0	0	0		771			0	0
Ending balance at Mar. 31, 2018	3,712,699	159,853	1,741	1,698,521		2,010,746			(107,673)	(50,488)
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	0	0	0		86,686			0	0
Other comprehensive income	21,597	0	0	0		0			21,597	0
Comprehensive income	108,283
Common stock issued:
Stock-based compensation plans, net	7,045	0	0	(32,220)		0			0	39,265
Purchase of treasury stock	(37,467)	0	0	0		0			0	(37,467)
Cash dividends:
Common stock ($0.15 per share in 2018 and $0.17 per share in 2019)	(28,183)	0	0	0		(28,183)			0	0
Preferred stock	(3,801)	0	0	0		(3,801)			0	0
Stock-based compensation expense, net	9,397	0	0	9,397		0			0	0
Other	(293)	0	0	0		(293)			0	0
Ending balance at Mar. 31, 2019	$ 3,835,870	$ 256,716	$ 1,752	1,689,792		2,235,824			$ (103,375)	(244,840)
Cash dividends:
Increase Adjustment Options, RSA and RSU						$ 36,000				$ 26,000
Decrease Adjustment Options RSA and RSU				$ 10,000

[1] (a) As previously disclosed in Associated Banc-Corp's 2018 Annual Report on Form 10-K, an adjustment was made to the March 31, 2018 stockholders' equity balances related to the grant and vesting of options, restricted stock awards, and restricted stock units awarded.  This adjustment increased Retained Earnings by $36 million, decreased Surplus $10 million, and increased Treasury Stock $26 million.  The reclassification had no impact on earnings, expenses, or total stockholders' equity.