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Summary of Significant Accounting Policies - Additional Information (Detail) |  |  | 1 Months Ended | 12 Months Ended |
--- | --- | --- | --- | --- | ---
Jan. 01, 2018 USD ($) | Sep. 20, 2017 | Mar. 31, 2017 USD ($) | Dec. 31, 2018 USD ($) | Dec. 31, 2017 USD ($)
Summary Of Significant Accounting Policies [Line Items] |  |  |  |  |
Period for federal funds purchased and sold |  |  |  | 1 day |
Average aggregate reserve |  |  |  | $ 12,600,000 | $ 11,400,000
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 |
Amount of fair value of capital over carrying value |  |  |  | $ 58,500,000 |
Percentage of fair value of capital over carrying value |  |  |  | 51.10% |
Number of times fair value of capital in excess of carrying value of goowill description |  |  |  | over fourteen times |
Other real estate owned |  |  |  | $ 600,000 | $ 674,000
Percentage of likelihood of realization of recognized tax benefit, minimum |  |  |  | 50.00% |
Share stock split ratio |  | 2 |  |  |
Amount of reclassification effect |  |  |  | $ 0 |
Corporate income tax rate |  |  |  | 21.00% |
ASU 2018-02 [Member] |  |  |  |  |
Summary Of Significant Accounting Policies [Line Items] |  |  |  |  |
Net effect on total stockholder's equity due to reclassification of tax effects | $ 0 |  |  |  |
Reclassification of tax effects from AOCI due to adoption of new Tax Cuts and Job Acts | $ 359,000 |  |  |  |
ASU 2016-02 [Member] |  |  |  |  |
Summary Of Significant Accounting Policies [Line Items] |  |  |  |  |
Expected right of use assets |  |  |  | $ 500,000 |
Expected liability related to lease |  |  |  | $ 500,000 |
Accounting Standards Update 2017-08 [Member] |  |  |  |  |
Summary Of Significant Accounting Policies [Line Items] |  |  |  |  |
Accelerated amortization expense adjustment |  |  | $ 30,000 |  |
Maximum [Member] |  |  |  |  |
Summary Of Significant Accounting Policies [Line Items] |  |  |  |  |
Maturity period of cash equivalents |  |  |  | 3 months |

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