Commitments and Contingencies - Summary of Contract Amounts of Credit-related Financial Instruments (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Commitments to Extend Credit [Member]
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Fixed Rate	$ 57,853	$ 56,513
Credit Enhancement Under FHLB of Chicago Mortgage Partnership Finance Program [Member]
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Fixed Rate	841	612
Commitments to Sell Loans [Member]
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Fixed Rate	10,917	6,617
Overdraft Protection Program Commitments [Member]
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Fixed Rate	4,129	3,894
Standby Letters of Credit, Variable [Member]
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Fixed Rate		33
Fixed Rate [Member] | Commitments to Extend Credit [Member]
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Fixed Rate	21,745	19,255
Fixed Rate [Member] | Credit Enhancement Under FHLB of Chicago Mortgage Partnership Finance Program [Member]
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Fixed Rate	841	612
Fixed Rate [Member] | Commitments to Sell Loans [Member]
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Fixed Rate	10,917	6,617
Fixed Rate [Member] | Overdraft Protection Program Commitments [Member]
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Fixed Rate	4,129	3,894
Variable Rate [Member] | Commitments to Extend Credit [Member]
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Fixed Rate	$ 36,108	37,258
Variable Rate [Member] | Standby Letters of Credit, Variable [Member]
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Fixed Rate		$ 33