Income Taxes - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income Taxes [Line Items]
Statutory rate	21.00%	21.00%	35.00%
Revaluation of deferred tax assets			$ 39,300,000
Bad debt reserves, created for tax purposes	$ 52,800,000
Unrecognized deferred income tax liability	13,000,000.0
Valuation allowance recorded	0	$ 0
AMT credit carryforwards	1,300,000	10,100,000
AMT credit carryforwards	1,272,000	2,545,000
Decrease in unrecognized tax benefits	0
Federal [Member]
Income Taxes [Line Items]
Operating loss carryforwards	$ 78,500,000	104,500,000
Federal tax credit carryforwards		1,800,000
Federal [Member] | Minimum [Member]
Income Taxes [Line Items]
Operating loss carryforwards, expiration year	2029
Federal [Member] | Maximum [Member]
Income Taxes [Line Items]
Operating loss carryforwards, expiration year	2033
State [Member]
Income Taxes [Line Items]
Operating loss carryforwards	$ 148,400,000	$ 165,600,000
State [Member] | Minimum [Member]
Income Taxes [Line Items]
Operating loss carryforwards, expiration year	2024
State [Member] | Maximum [Member]
Income Taxes [Line Items]
Operating loss carryforwards, expiration year	2033
AnchorBank WI [Member]
Income Taxes [Line Items]
Bad debt reserves, created for tax purposes	$ 50,900,000
Lafayette Savings Bank [Member]
Income Taxes [Line Items]
Bad debt reserves, created for tax purposes	$ 1,900,000