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Summary of Significant Accounting Policies (Detail) | 9 Months Ended | 12 Months Ended
--- | --- | ---
Sep. 30, 2016 shares | Sep. 30, 2015 USD ($) shares | Dec. 31, 2015 USD ($) shares | Dec. 31, 2014 USD ($) shares | Dec. 31, 2013 USD ($) shares
Number of Branches |  |  | 10 |  |
Goodwill, Impairment Loss |  |  | $ 0 | $ 0 | $ 0
Employee Service Share-based Compensation, Nonvested Awards, Compensation Not yet Recognized, Stock Options |  |  | $ 0 |  |
Stock Issued During Period, Shares, Share-based Compensation, Net of Forfeitures (in Shares) | shares | 360,815 |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period (in Shares) | shares | 0 | 1,025 | 2,175 | 11,223 |
Payments for Stock Options Exercised |  | $ (6,000) | $ 7,000 | $ 50,000 | 77,000
Employee Stock Option [Member] |  |  |  |  |
Allocated Share-based Compensation Expense |  |  | $ 0 | $ 0 | $ 0
Restricted Stock [Member] |  |  |  |  |
Stock Issued During Period, Shares, Share-based Compensation, Net of Forfeitures (in Shares) | shares |  |  | 585 | 0 | 0
Core Deposits [Member] |  |  |  |  |
Finite-Lived Intangible Asset, Useful Life |  |  | 10 years |  |
Minimum [Member] | Furniture, Fixtures, and Equipment [Member] |  |  |  |  |
Property, Plant and Equipment, Useful Life |  |  | 3 years |  |
Minimum [Member] | Building and Building Improvements [Member] |  |  |  |  |
Property, Plant and Equipment, Useful Life |  |  | 3 years |  |
Maximum [Member] | Furniture, Fixtures, and Equipment [Member] |  |  |  |  |
Property, Plant and Equipment, Useful Life |  |  | 20 years |  |
Maximum [Member] | Building and Building Improvements [Member] |  |  |  |  |
Property, Plant and Equipment, Useful Life |  |  | 40 years |  |

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