Retirement Plans, Pension and Postretirement Plans Table (Details) - USD ($) $ in Thousands		12 Months Ended
	Feb. 01, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Defined Benefit Plan Disclosure [Line Items]
Fair Value Of Plan Assets As A Percentage Of Net Benefit Obligation		170.00%	167.00%
Pension Plan [Member]
Change in Fair Value of Plan Assets
Fair value of plan assets at beginning of year		$ 390,564	$ 331,609
Actual return on plan assets		67,377	(14,609)
Employer contributions		0	4,340
Gross benefits paid		(15,907)	(10,582)
Bank Mutual plan assets transferred at December 31, 2018			79,805
Fair value of plan assets at end of year(a)		442,034	390,564	$ 331,609
Change in Benefit Obligation
Net benefit obligation at beginning of year		233,658	186,423
Service cost		7,263	7,540	6,955
Interest cost		9,752	9,125	7,121
Actuarial (gain) loss		25,810	(8,000)
Gross benefits paid		(15,907)	(10,582)
Lump sums paid		0	0
Bank Mutual benefit obligations transferred at December 31, 2018			51,549
Net benefit obligation at end of year(a)		260,576	233,658	186,423
Funded (unfunded) status		181,458	156,906
Noncurrent assets		181,458	156,906
Current liabilities		0	0
Noncurrent liabilities		0	0
Asset (Liability) Recognized on the Consolidated Balance Sheets		181,458	156,906
Retirement Account Plan Prior to Merger [Member]
Change in Benefit Obligation
Interest cost			6,727
Bank Mutual Pension
Change in Fair Value of Plan Assets
Fair value of Bank Mutual plan assets at February 1, 2018	$ 59,445
Actual return on plan assets			(1,665)
Employer contributions			37,537
Gross benefits paid			(15,513)
Bank Mutual plan assets transferred at December 31, 2018			(79,805)
Fair value of plan assets at end of year(a)		0
Change in Benefit Obligation
Net benefit obligation at beginning of year		0
Net Bank Mutual benefit obligation at February 1, 2018	66,364
Service cost			0
Interest cost			2,398
Actuarial (gain) loss			(1,701)
Gross benefits paid			(2,644)
Lump sums paid			(12,868)
Bank Mutual benefit obligations transferred at December 31, 2018			(51,549)
Net benefit obligation at end of year(a)			0
Funded (unfunded) status			0
Noncurrent assets			0
Current liabilities			0
Noncurrent liabilities			0
Asset (Liability) Recognized on the Consolidated Balance Sheets			0
Postretirement Plan
Change in Fair Value of Plan Assets
Fair value of plan assets at beginning of year		0	0
Fair value of Bank Mutual plan assets at February 1, 2018	0		0
Actual return on plan assets		0	0
Employer contributions		270	292
Gross benefits paid		(270)	(292)
Bank Mutual plan assets transferred at December 31, 2018		0	0
Fair value of plan assets at end of year(a)		0	0	0
Change in Benefit Obligation
Net benefit obligation at beginning of year		2,523	2,478
Net Bank Mutual benefit obligation at February 1, 2018	$ 0		576
Service cost		0	0
Interest cost		104	108	101
Actuarial (gain) loss		188	(347)
Gross benefits paid		(270)	(292)
Lump sums paid		0	0
Bank Mutual benefit obligations transferred at December 31, 2018		0	0
Net benefit obligation at end of year(a)		2,545	2,523	$ 2,478
Funded (unfunded) status		(2,545)	(2,523)
Noncurrent assets		0	0
Current liabilities		(214)	(219)
Noncurrent liabilities		(2,330)	(2,304)
Asset (Liability) Recognized on the Consolidated Balance Sheets		$ (2,545)	$ (2,523)