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Fair Value of Financial Instruments - Additional Information (Detail) - USD ($) $ in Thousands | 9 Months Ended |  |
--- | --- | --- | ---
Sep. 30, 2018 | Dec. 31, 2017 | Sep. 30, 2017
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Interest-bearing deposits maturing date | 90 days |  |
Collateral dependent impaired loans categorized as Level 3 | $ 2,811 | $ 1,745 | $ 1,979
Specific allocation for collateral dependent impaired loans | 148 | 106 | $ 123
Level 3 [Member] |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Collateral dependent impaired loans categorized as Level 3 | $ 822 | $ 508 |

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