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Recent Developments Including Mergers and Acquisitions - Additional Information (Detail) $ in Thousands |  |  |  | 9 Months Ended |
--- | --- | --- | --- | --- | ---
Aug. 31, 2018 USD ($) ft² Floor | Jan. 11, 2018 USD ($) Location | Jul. 31, 2017 shares | Sep. 30, 2018 USD ($) Community | Dec. 31, 2017 USD ($)
Business Combination Separately Recognized Transactions [Line Items] |  |  |  |  |
Goodwill |  |  |  | $ 79,733 | $ 54,042
Number of additional banking communities | Community |  |  |  | 5 |
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 |  |
First Bank & Trust Company [Member] |  |  |  |  |
Business Combination Separately Recognized Transactions [Line Items] |  |  |  |  |
Date of acquisition |  | Jan. 11, 2018 |  |  |
Total assets acquired |  | $ 290,000 |  |  |
Loans |  | 247,000 |  |  |
Deposits |  | 251,000 |  |  |
Equity capital |  | 36,000 |  |  |
Intangibles assets, net |  | 6,300 |  |  |
Goodwill |  | $ 19,100 |  |  |
Fair value estimates period |  | 1 year |  |  |
First Bank of Chandler [Member] |  |  |  |  |
Business Combination Separately Recognized Transactions [Line Items] |  |  |  |  |
Date of acquisition |  | Jan. 11, 2018 |  |  |
Total assets acquired |  | $ 88,000 |  |  |
Loans |  | 66,000 |  |  |
Deposits |  | 79,000 |  |  |
Equity capital |  | 11,000 |  |  |
Intangibles assets, net |  | 2,200 |  |  |
Goodwill |  | $ 6,600 |  |  |
Fair value estimates period |  | 1 year |  |  |
Number of locations acquired | Location |  | 2 |  |  |
BFTower LLC [Member] | Cotter Ranch Tower [Member] |  |  |  |  |
Business Combination Separately Recognized Transactions [Line Items] |  |  |  |  |
Contract price | $ 21,000 |  |  |  |
Number of square feet | ft² | 507,000 |  |  |  |
Number of floors | Floor | 36 |  |  |  |
Date of acquisition | Aug. 31, 2018 |  |  |  |

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