Borrowings - Additional Information (Detail) (USD $)	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013
Debt Instrument [Line Items]
Weighted average rate of federal funds purchased		0.36%
Weighted average rate of retail repurchase agreements	0.13%	0.38%
Federal funds purchased outstanding	$ 0us-gaap_FederalFundsPurchased	$ 16,000,000us-gaap_FederalFundsPurchased
FHLB borrowings	90,000,000	150,000,000
Number of FHLB letters of credit	2
Letters of credit held to collateralize public unit deposits	6,180,000
Qualifying loans	981,000	1,130,000,000
Junior subordinated debentures issued	15,460,000
Libor rate	2.95%
Debentures mature date	Oct. 08, 2033
Unrelated Financial Institution
Debt Instrument [Line Items]
Unsecured, committed line of credit, outstanding amount	2,000,000
Unsecured, committed line of credit, borrowing capacity	15,000,000
Unsecured, committed line of credit, interest rate	One-month LIBOR plus 2.00%
Unsecured, committed line of credit, base rate	2.00%
Unsecured, committed line of credit, maturity date	Apr. 30, 2015
Wholesale Repurchase Agreements
Debt Instrument [Line Items]
Weighted average contractual rate	3.71%	3.71%
FHLB Prepaid borrowing amount		8,150,000
FHLB Borrowings
Debt Instrument [Line Items]
Weighted average contractual rate	4.07%	4.12%
FHLB Prepaid borrowing amount		11,470,000
FHLB borrowings	60,000,000
FHLB Debt repayments	5,010,000
Gain on repayment of FHLB borrowings		296,000
Unused borrowing capacity	409,190,000
Federal Home Loan Bank 4.21% Due 2017
Debt Instrument [Line Items]
FHLB Prepaid borrowing amount	50,000,000
FHLB Interest rate	4.21%
FHLB maturity date	2017
Federal Home Loan Bank 4.15% Due 2017
Debt Instrument [Line Items]
FHLB Prepaid borrowing amount	10,000,000
FHLB Interest rate	4.15%
FHLB maturity date	2017
FHLB borrowings	$ 50,000,000

Number Of Federal Home Loan Bank Advances

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Prepayment Of Federal Home Loan Bank Advances

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Weighted average contractual rate.

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Weighted Average Rate of Federal Funds Purchased

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Weighted Average Rate of Retail Repurchase Agreements

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Percentage points added to the reference rate to compute the variable rate on the debt instrument.

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Date when the debt instrument is scheduled to be fully repaid, in CCYY-MM-DD format.

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Amount of unused borrowing capacity under the long-term financing arrangement that is available to the entity as of the balance sheet date.

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Amount of securities, mortgage loans, or other financial instruments pledged as collateral for deposits.

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Amount of short term borrowing where a bank borrows, at the federal funds rate, from another bank.

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Discloses the year of maturity, when only one maturity date applies. for the advances from the Federal Home Loan Bank, by branch, as of the Balance Sheet date.

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Discloses the single interest rate [if] applicable to the advances from the Federal Home Loan Bank, by branch, as of the Balance Sheet date.

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Amount of the collateral pledged in support of federal home loan bank advances outstanding.

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Amount of repayments and penalties incurred in the satisfaction or roll-over of Federal Home Loan Bank (FHLB) advance.

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Including both current and noncurrent portions, Federal Home Loan Bank borrowings initially due beyond one year or beyond the normal operating cycle if longer.

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Difference between the fair value of payments made and the carrying amount of debt which is extinguished prior to maturity.

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The carrying value as of the balance sheet date of the current and noncurrent portions of long-term obligations drawn from a line of credit, which is a bank's commitment to make loans up to a specific amount. Examples of items that might be included in the application of this element may consist of letters of credit, standby letters of credit, and revolving credit arrangements, under which borrowings can be made up to a maximum amount as of any point in time conditional on satisfaction of specified terms before, as of and after the date of drawdowns on the line. Includes short-term obligations that would normally be classified as current liabilities but for which (a) postbalance sheet date issuance of a long term obligation to refinance the short term obligation on a long term basis, or (b) the enterprise has entered into a financing agreement that clearly permits the enterprise to refinance the short-term obligation on a long term basis and the following conditions are met (1) the agreement does not expire within 1 year and is not cancelable by the lender except for violation of an objectively determinable provision, (2) no violation exists at the BS date, and (3) the lender has entered into the financing agreement is expected to be financially capable of honoring the agreement.

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Date the credit facility terminates, in CCYY-MM-DD format.

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Description of the interest rate for the amounts borrowed under the credit facility, including the terms and the method for determining the interest rate (for example, fixed or variable, LIBOR plus a percentage, increasing rate, timing of interest rate resets, remarketing provisions).

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Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

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The interest rate applicable to the portion of the carrying amount of long-term borrowings outstanding as of the balance sheet date, including current maturities, which accrues interest at a rate subject to change from time to time.

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The cash inflow from a borrowing where a lender is placed in a lien position behind debt having a higher priority of repayment (senior) in liquidation of the entity's assets or underlying collateral.

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