Income Taxes - Additional Information (Detail) - USD ($)	3 Months Ended
	Mar. 31, 2019	Dec. 31, 2018
Income Taxes [Line Items]
Decrease in unrecognized tax benefits	$ 0
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	6,300,000	10,100,000
Tax credit carryforwards reclassified to current tax asset	3,800,000
AMT credit carryforwards	$ 2,545,000	2,545,000
Minimum [Member]
Income Taxes [Line Items]
AMT credit carryforwards, expiration year	2018
Maximum [Member]
Income Taxes [Line Items]
AMT credit carryforwards, expiration year	2021
Federal [Member]
Income Taxes [Line Items]
Operating loss carryforwards	$ 97,100,000	104,500,000
Federal tax credit carryforwards	$ 3,100,000	1,800,000
Federal [Member] | Minimum [Member]
Income Taxes [Line Items]
Operating loss carryforwards, expiration year	2028
Tax credits carryforwards, expiration year	2025
Federal [Member] | Maximum [Member]
Income Taxes [Line Items]
Operating loss carryforwards, expiration year	2033
Tax credits carryforwards, expiration year	2039
State [Member]
Income Taxes [Line Items]
Operating loss carryforwards	$ 165,000,000.0	$ 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