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Fair Value of Instruments - Additional Information (Detail) - USD ($) | 9 Months Ended | 12 Months Ended |
--- | --- | --- | ---
Sep. 30, 2016 | Dec. 31, 2015 | Sep. 30, 2015
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Interest-bearing deposits maturing date | 90 days |  |
Fair value of collateral dependent impaired loans categorized as Level 3 | $ 1,406,000 | $ 2,136,000 | $ 2,541,000
Specific allocation for collateral dependent impaired loans | 125,000 | 330,000 | $ 465,000
Asset impairment charges | 0 | 0 |
Level 3 [Member] |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Fair value of collateral dependent impaired loans categorized as Level 3 | $ 766,000 | $ 549,000 |

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