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Subsequent Events - Additional Information (Detail) $ / shares in Units, $ in Millions | Jan. 01, 2019 USD ($) Office $ / shares shares | Dec. 31, 2018 shares | Dec. 31, 2017 shares
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Subsequent Event [Line Items] |  |  |
Common stock, shares outstanding | shares |  | 10,400,000 | 10,400,000
Subsequent Event [Member] | Bank of Geneva [Member] |  |  |
Subsequent Event [Line Items] |  |  |
Number of full-service offices | Office | 6 |  |
Subsequent Event [Member] | Limberlost Bancshares, Inc. [Member] |  |  |
Subsequent Event [Line Items] |  |  |
Common stock issued in exchange of each outstanding share | shares | 1,830 |  |
Cash payment for exchange of each share | $ / shares | $ 8,465.00 |  |
Common stock, shares outstanding | shares | 1,000 |  |
Share price | $ / shares | $ 38.49 |  |
Total consideration for acquisition | $ 78.9 |  |
Cash paid for acquisition | 8.5 |  |
Stock issued for acquisition | 70.4 |  |
Assets acquired, loans carrying value | 259.3 |  |
Liabilities assumed, deposits carrying value | 206.6 |  |
Liabilities assumed, other borrowings carrying value | $ 49.5 |  |

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