Acquisition of MSB Financial Corp. - Summary of Assets Acquired and Liabilities Assumed Through Merger at Fair Value (Detail) - USD ($) $ in Thousands			6 Months Ended
		Jul. 10, 2020	Dec. 31, 2020
Business Acquisition [Line Items]
Bargain purchase gain			$ (3,053)
MSB Financial Corporation [Member]
Business Acquisition [Line Items]
Cash paid for acquisition		$ 9,830
Value of stock issued		45,133
Total purchase price		54,963
Cash and cash equivalents		14,126
Investment securities		3,490
Loans receivable		530,244
Premises and equipment		4,477
FHLB stock		3,345
Accrued interest receivable		1,701
Core deposit intangibles		690
Bank owned life insurance		14,663
Deferred income taxes, net		3,881
Other assets		5,325
Total assets acquired		581,942
Deposits		460,178
FHLB borrowings		62,900
Advance payments by borrowers for taxes		794
Other liabilities		54
Total liabilities assumed		523,926
Net assets acquired		58,016
Bargain purchase gain		(3,053)
MSB Financial Corporation [Member] | As Recorded by MSB [Member]
Business Acquisition [Line Items]
Cash and cash equivalents		14,126
Investment securities		4,000
Loans receivable		537,589
Allowance for loan losses		(6,037)
Premises and equipment		7,698
FHLB stock		3,345
Accrued interest receivable		1,701
Bank owned life insurance		14,663
Deferred income taxes, net		1,729
Other assets		4,830
Total assets acquired		583,644
Deposits		458,392
FHLB borrowings		62,900
Advance payments by borrowers for taxes		794
Other liabilities		810
Total liabilities assumed		522,896
MSB Financial Corporation [Member] | Fair Value Adjustments [Member]
Business Acquisition [Line Items]
Investment securities	[1]	(510)
Loans receivable	[2]	(7,345)
Allowance for loan losses	[3]	6,037
Premises and equipment	[4]	(3,221)
Core deposit intangibles	[5]	690
Deferred income taxes, net	[6]	2,152
Other assets	[7]	495
Total assets acquired		(1,702)
Deposits	[8]	1,786
Other liabilities	[9]	(756)
Total liabilities assumed		$ 1,030

[1] Represents the fair value adjustments on investment securities.

[2] Represents the fair value adjustments on the net book value of loans, which includes an interest rate mark and credit mark adjustment and the reversal of deferred fees/costs and premiums.

[3] Represents the elimination of MSB’s allowance for loan losses.

[4] Represents the fair value adjustments to reflect the fair value of land and buildings and premises and equipment, which will be amortized on a straight-line basis over the estimated useful lives of the individual assets.

[5] Represents the intangible assets recorded to reflect the fair value of core deposits.  The core deposit asset was recorded as an identifiable intangible asset and will be amortized on an accelerated basis over the estimated average life of the deposit base.

[6] Represents an adjustment to net deferred tax assets resulting from the fair value adjustments related to the acquired assets, liabilities assumed and identifiable intangible assets recorded.

[7] Represents an adjustment to other assets acquired.

[8] Represents fair value adjustments on time deposits, which will be treated as a reduction of interest expense over the remaining term of the time deposits.

[9] Represents an adjustment to other liabilities assumed.