Commitments and Contingencies - Summary of Contractual Amounts of Off-balance Sheet Credit Related Financial Instruments (Detail) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Fixed Rate	$ 83,281	$ 67,669
Commitments to Extend Credit [Member]
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Fixed Rate	62,062	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	725	612
Commitments to Sell Loans [Member]
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Fixed Rate	16,660	6,617
Overdraft Protection Program Commitments [Member]
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Fixed Rate	3,811	3,894
Standby Letters of Credit [Member]
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Fixed Rate	23	33
Fixed Rate [Member]
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Fixed Rate	44,200	30,378
Fixed Rate [Member] | Commitments to Extend Credit [Member]
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Fixed Rate	23,004	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	725	612
Fixed Rate [Member] | Commitments to Sell Loans [Member]
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Fixed Rate	16,660	6,617
Fixed Rate [Member] | Overdraft Protection Program Commitments [Member]
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Fixed Rate	3,811	3,894
Variable Rate [Member]
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Fixed Rate	39,081	37,291
Variable Rate [Member] | Commitments to Extend Credit [Member]
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Fixed Rate	39,058	37,258
Variable Rate [Member] | Standby Letters of Credit [Member]
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Fixed Rate	$ 23	$ 33