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Loans (Impaired Loans) - Additional Information (Detail) - USD ($) $ in Thousands | 9 Months Ended |  |
--- | --- | --- | ---
Sep. 30, 2017 | Dec. 31, 2016 | Sep. 30, 2016
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |
Impaired loans classified as troubled debt restructured | $ 540 | $ 557 | $ 562
Maximum time for re-evaluation (in months) | 12 months |  |
Re-evaluation period for real estate | 2 years |  |
Unsecured consumer loans, credit card credits and overdraft lines of credit reach | 90 days |  |
Delinquent period for charging down consumer loans | 120 days |  |
Delinquent period for charging down commercial and agricultural credits | 120 days |  |
Foreclosed residential real estate property | $ 615 | $ 774 |
Consumer Real Estate [Member] |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |
Foreclosed residential real estate property | 25 |  | 808
Residential real estate properties foreclosure proceedings | $ 59 |  | $ 211

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