Income Taxes - Additional Information (Detail) - USD ($)	1 Months Ended	3 Months Ended		12 Months Ended
	May 31, 2016	Dec. 31, 2017	Sep. 30, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Taxes [Line Items]
Estimated revaluation of deferred tax assets		$ 39,300,000			$ 39,300,000
Statutory rate					35.00%	35.00%	35.00%
Bad debt reserves, created for tax purposes		52,800,000			$ 52,800,000
Unrecognized deferred income tax liability		13,000,000			13,000,000
Valuation allowance recorded		0			0	$ 0
Operating loss carryforwards, federal		130,700,000			130,700,000	162,900,000
AMT carryforwards		25,084,000			25,084,000	19,523,000
Federal tax credits		5,516,000			5,516,000	35,000
Operating loss carryforwards, state		203,600,000			203,600,000	206,300,000
Unrecognized tax benefits, if recognized, would favorably affect the effective tax rate		900,000			900,000
Decrease in unrecognized tax benefits					(200,000)
Interest and penalties					10,000	100,000	$ 400
Interest and penalties, accrued		100,000			100,000	100,000
Uncertain tax position reversal			$ 200,000		173,000	$ 2,000	$ 4,000
State [Member]
Income Taxes [Line Items]
Tax credit		1,300,000			$ 1,300,000
Minimum [Member] | State Net Operating Loss [Member]
Income Taxes [Line Items]
Operating loss carryforwards, expiration date					2024
Minimum [Member] | Federal Net Operating Loss [Member]
Income Taxes [Line Items]
Operating loss carryforwards, expiration date					2027
Minimum [Member] | Federal Tax Credits [Member]
Income Taxes [Line Items]
Operating loss carryforwards, expiration date					2028
Maximum [Member] | State Net Operating Loss [Member]
Income Taxes [Line Items]
Operating loss carryforwards, expiration date					2037
Maximum [Member] | Federal Net Operating Loss [Member]
Income Taxes [Line Items]
Operating loss carryforwards, expiration date					2037
Maximum [Member] | Federal Tax Credits [Member]
Income Taxes [Line Items]
Operating loss carryforwards, expiration date					2033
ONB Insurance Group, Inc. [Member]
Income Taxes [Line Items]
Additional tax expense to record deferred tax liability	$ 8,300,000
Scenario, Forecast [Member]
Income Taxes [Line Items]
Statutory rate				21.00%
AnchorBank WI [Member]
Income Taxes [Line Items]
Bad debt reserves, created for tax purposes		50,900,000			$ 50,900,000
Lafayette Savings Bank [Member]
Income Taxes [Line Items]
Bad debt reserves, created for tax purposes		$ 1,900,000			$ 1,900,000