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Fair Value of Financial Instruments - Additional Information (Detail) - USD ($) | 12 Months Ended |
--- | --- | ---
Dec. 31, 2017 | Dec. 31, 2016
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 | $ 1,745,000 | $ 1,852,000
Specific allocation for collateral dependent impaired loans | 106,000 | 135,000
Asset impairment charges | 0 |
Level 3 [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Collateral dependent impaired loans categorized as Level 3 | $ 1,600,000 | $ 1,700,000

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