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Fair Value Measurements - Balances of Assets Measured at Fair Value on a Recurring Basis (Detail) - USD ($) $ in Thousands | Mar. 31, 2018 | Dec. 31, 2017
--- | --- | ---
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Fair Value | $ 93,699 | $ 89,255 | [1]
Recurring basis |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Fair Value | 93,699 | 89,255 |
Recurring basis | U.S. agency and mortgage-backed securities |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Fair Value | 79,108 | 74,804 |
Recurring basis | Obligations of states and political subdivisions |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Fair Value | 14,591 | 14,451 |
Recurring basis | Quoted Prices in Active Markets for Identical Assets (Level 1) |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Fair Value | 0 | 0 |
Recurring basis | Quoted Prices in Active Markets for Identical Assets (Level 1) | U.S. agency and mortgage-backed securities |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Fair Value | 0 | 0 |
Recurring basis | Quoted Prices in Active Markets for Identical Assets (Level 1) | Obligations of states and political subdivisions |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Fair Value | 0 | 0 |
Recurring basis | Significant Other Observable Inputs (Level 2) |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Fair Value | 93,699 | 89,255 |
Recurring basis | Significant Other Observable Inputs (Level 2) | U.S. agency and mortgage-backed securities |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Fair Value | 79,108 | 74,804 |
Recurring basis | Significant Other Observable Inputs (Level 2) | Obligations of states and political subdivisions |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Fair Value | 14,591 | 14,451 |
Recurring basis | Significant Unobservable Inputs (Level 3) |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Fair Value | 0 | 0 |
Recurring basis | Significant Unobservable Inputs (Level 3) | U.S. agency and mortgage-backed securities |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Fair Value | 0 | 0 |
Recurring basis | Significant Unobservable Inputs (Level 3) | Obligations of states and political subdivisions |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Fair Value | $ 0 | $ 0 |
[1] | Derived from audited consolidated financial statements.

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