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Recent Developments Including Mergers and Acquisitions - Additional Information (Detail) $ in Thousands |  |  | 12 Months Ended |  |  |
--- | --- | --- | --- | --- | --- | ---
Jan. 12, 2018 | Jul. 31, 2017 shares | Dec. 31, 2017 USD ($) Community | Dec. 31, 2016 USD ($) | Dec. 31, 2015 USD ($) | Oct. 08, 2015 USD ($)
Business Combination Separately Recognized Transactions [Line Items] |  |  |  |  |  |
Goodwill |  |  | $ 54,042 | $ 54,042 | $ 54,042 |
Number of additional banking communities | Community |  |  | 2 |  |  |
COMMON STOCK [Member] |  |  |  |  |  |
Business Combination Separately Recognized Transactions [Line Items] |  |  |  |  |  |
Stock split description |  |  | On July 31, 2017, the Company completed a two-for-one stock split of the Company’s outstanding shares of common stock. |  |  |
Stock split conversion ratio |  | 2 |  |  |  |
Stock payable in form of dividend, payable date |  | Jul. 31, 2017 |  |  |  |
Stock payable in form of dividend, record date |  | Jul. 17, 2017 |  |  |  |
Additional shares received by stockholders for each share held | shares |  | 1 |  |  |  |
Bank of Commerce [Member] |  |  |  |  |  |
Business Combination Separately Recognized Transactions [Line Items] |  |  |  |  |  |
Total assets acquired |  |  |  |  |  | $ 196,000
Loans |  |  |  |  |  | 147,000
Deposits |  |  |  |  |  | 175,000
Equity capital |  |  |  |  |  | $ 22,000
Percentage of voting interests acquired |  |  |  |  |  | 100.00%
Intangibles assets, net |  |  |  |  |  | $ 7,100
Goodwill |  |  |  |  |  | $ 9,400
Subsequent Event [Member] | First Bank & Trust Company [Member] |  |  |  |  |  |
Business Combination Separately Recognized Transactions [Line Items] |  |  |  |  |  |
Date of acquisition | Jan. 12, 2018 |  |  |  |  |
Subsequent Event [Member] | First Bank of Chandler [Member] |  |  |  |  |  |
Business Combination Separately Recognized Transactions [Line Items] |  |  |  |  |  |
Date of acquisition | Jan. 12, 2018 |  |  |  |  |

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