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Commitments and Contingent Liabilities - Additional Information (Detail) - USD ($) | Mar. 31, 2018 | Dec. 31, 2017
--- | --- | ---
Loss Contingencies [Line Items] |  |
Notional Amount Of Performance Standby Letters Of Credit | $ 400,000 |
Notional Amount Of Commercial Letters Of Credit | 0 |
Notional Amount Of Financial Standby Letters Of Credit | 0 |
Financial instrument of credit risk | 200,000 | $ 200,000
Unfunded commitment liability | 5,200,000 |
Minimum [Member] |  |
Loss Contingencies [Line Items] |  |
Loss Contingency, Estimate of Possible Loss | 0 |
Maximum [Member] |  |
Loss Contingencies [Line Items] |  |
Loss Contingency, Estimate of Possible Loss | $ 1,000,000 |

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