Fair Value - Summary of Carrying Value and Fair Values of the Bank's Financial Instruments (Details) - USD ($)	Mar. 31, 2019	Dec. 31, 2018
Financial assets:
Estimated fair value	$ 233,691,000	$ 243,808,000
Securities held to maturity, fair value	3,806,000	3,785,000
Loans held for sale	0	0
Carrying amount
Financial assets:
Cash and due from banks, interest-bearing deposits in financial institutions	112,196,000	94,681,000
Federal funds sold	8,125,000	10,762,000
Estimated fair value	233,691,000	243,808,000
Securities held to maturity, fair value	3,727,000	3,734,000
Loans held for sale	72,870,000	57,618,000
Restricted equity securities	14,145,000	12,038,000
Loans	1,467,786,000	1,429,794,000
Accrued interest receivable	6,446,000	5,964,000
Other assets	34,664,000	34,489,000
Financial liabilities:
Deposits	1,678,802,000	1,570,008,000
Federal Home Loan Bank advances	75,000,000	125,000,000
Other liabilities	1,506,000	2,753,000
Fair value
Financial assets:
Loans	1,466,147,000	1,442,082,000
Fair value | Level 1
Financial assets:
Cash and due from banks, interest-bearing deposits in financial institutions	112,196,000	94,681,000
Federal funds sold	8,125,000	10,762,000
Fair value | Level 2
Financial assets:
Estimated fair value	233,691,000	243,808,000
Securities held to maturity, fair value	3,806,000	3,785,000
Loans held for sale	74,193,000	58,596,000
Accrued interest receivable	6,446,000	5,964,000
Other assets	34,664,000	34,489,000
Financial liabilities:
Federal Home Loan Bank advances	75,663,000	126,548,000
Fair value | Level 3 Fair Value Measurements
Financial liabilities:
Deposits	1,612,455,000	1,504,101,000
Other liabilities	$ 1,506,000	$ 2,753,000