Fair Values of Financial Instruments and Interest Rate Risk - Comparison of Carrying Amounts and Estimated Fair Value of Financial Instruments (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
FINANCIAL ASSETS
Securities held to maturity	$ 11,461	$ 11,934
Loans held for investment, net	354,413	339,122
Accrued interest receivable	1,709	1,629
FINANCIAL LIABILITIES
Long-term debt	9,534	9,534
Accrued interest payable	148	151
Carrying Value [Member]
FINANCIAL ASSETS
Cash and cash equivalents	70,403	45,968
Securities available for sale	95,743	105,899
Securities held to maturity	11,458	11,990
Loans held for investment, net	356,871	339,122
Loans held for sale	4,414	5,823
Restricted stock	1,067	1,052
Mortgage servicing rights	2,125	2,271
Accrued interest receivable	1,709	1,629
FINANCIAL LIABILITIES
Deposits	512,628	485,719
Short-term borrowings	1,752	2,674
Long-term debt	9,534	9,534
Accrued interest payable	148	151
Estimated Fair Value [Member]
FINANCIAL ASSETS
Cash and cash equivalents	70,379	45,995
Securities available for sale	95,743	105,899
Securities held to maturity	11,461	11,934
Loans held for investment, net	359,325	337,348
Loans held for sale	4,414	5,685
Restricted stock	1,067	1,052
Mortgage servicing rights	3,310	3,313
Accrued interest receivable	1,709	1,629
FINANCIAL LIABILITIES
Deposits	481,300	447,784
Short-term borrowings	1,752	2,674
Long-term debt	9,658	9,673
Accrued interest payable	148	151
Level 1 [Member]
FINANCIAL ASSETS
Cash and cash equivalents	67,913	43,478
Securities available for sale		4,014
Restricted stock	1,067	1,052
Level 2 [Member]
FINANCIAL ASSETS
Cash and cash equivalents	2,466	2,517
Securities available for sale	95,743	101,885
Securities held to maturity	11,461	11,934
Loans held for sale	4,414	5,685
Mortgage servicing rights	3,310	3,313
FINANCIAL LIABILITIES
Deposits	481,300	447,784
Short-term borrowings	1,752	2,674
Level 3 [Member]
FINANCIAL ASSETS
Loans held for investment, net	359,325	337,348
Accrued interest receivable	1,629	1,629
FINANCIAL LIABILITIES
Long-term debt	9,658	9,673
Accrued interest payable	$ 148	$ 151

Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

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Fair value portion of currency on hand as well as demand deposits with banks or financial institutions. Includes other kinds of accounts that have the general characteristics of demand deposits. Also includes short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates.

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Fair value portion of deposit liabilities held by the entity, including, but not limited to, foreign and domestic, interest and noninterest bearing, demand deposits, saving deposits, negotiable orders of withdrawal (NOW) and time deposits.

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Fair value of investments in debt securities classified as held-to-maturity.

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Amount of interest payable on debt, including, but not limited to, trade payables.

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Carrying amount as of the balance sheet date of interest earned but not received. Also called accrued interest or accrued interest receivable.

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Fair value portion of investments in Federal Home Loan Bank (FHLBank) stock.

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Amount after allowance and deduction of deferred interest and fees, unamortized costs and premiums and discounts from face amounts, of loans and leases held in portfolio, including but not limited to, commercial and consumer loans. Excludes loans and leases covered under loss sharing agreements and loans held for sale.

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Amount, after unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

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Fair value of an asset representing net future revenue from contractually specified servicing fees, late charges, and other ancillary revenues, in excess of future costs related to servicing arrangements.

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