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Summary of Significant Accounting Policies - Additional Information (Detail) |  |  | 1 Months Ended | 12 Months Ended |  |
--- | --- | --- | --- | --- | --- | ---
Dec. 31, 2017 USD ($) | Sep. 20, 2017 | Mar. 31, 2017 USD ($) | Dec. 31, 2017 USD ($) | Jan. 19, 2018 shares | Dec. 31, 2016 USD ($)
Summary Of Significant Accounting Policies [Line Items] |  |  |  |  |  |
Period for federal funds purchased and sold |  |  |  | 1 day |  |
Average aggregate reserve | $ 11,400,000 |  |  | $ 11,400,000 |  | $ 5,000,000
Loan non-accrual classification period |  |  |  | 90 days |  |
Days to charged consumer loans to the value of the collateral |  |  |  | 90 days |  |
Maximum time for re-evaluation (in months) |  |  |  | 12 months |  |
Re-evaluation period for real estate |  |  |  | 2 years |  |
Other real estate owned | 674,000 |  |  | $ 674,000 |  | $ 774,000
Percentage of likelihood of realization of recognized tax benefit, minimum |  |  |  | 50.00% |  |
Share stock split ratio |  | 2 |  |  |  |
Amount of reclassification effect |  |  |  | $ 0 |  |
Accelerated amortization expense adjustment |  |  | $ 30,000 |  |  |
Adjustment of deferred tax assets |  |  |  | $ (8,000) |  |
Subsequent Event [Member] |  |  |  |  |  |
Summary Of Significant Accounting Policies [Line Items] |  |  |  |  |  |
Stock Repurchase Program, Number of Shares Authorized to be Repurchased | shares |  |  |  |  | 400,000 |
Maximum [Member] |  |  |  |  |  |
Summary Of Significant Accounting Policies [Line Items] |  |  |  |  |  |
Maturity period of cash equivalents |  |  |  | 3 months |  |
Adjustment of deferred tax assets | $ 8,000 |  |  |  |  |

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