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Nature of Banking Activities and Significant Accounting policies - Additional Information (Detail) | 12 Months Ended
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Dec. 31, 2017 USD ($) Entity | Dec. 31, 2016 USD ($)
Nature Of Banking Activities And Significant Accounting Policies [Line Items] |  |
Number of accounts included by parent company | Entity | 6 |
Gain (loss) on rate lock commitments | $ 0 |
Accrual status of loan | 90 days |
Troubled debt restructurings (TDRs), amount | $ 333,000 | $ 460,000
Bank-owned life insurance, death benefits received | 720,000 | 527,000
Tax Cuts and Jobs Act of 2017, Income tax expense | $ 752,000 |
Largest amount of tax benefit realized by taxing authority | 50.00% |
Liability for unrecognized tax benefits | $ 0 | 0
Advertising cost | 379,000 | 402,000
Reclassification of tax effects stranded in accumulated other comprehensive loss by tax rate change | 0 |
Life Insurance Product Line |  |
Nature Of Banking Activities And Significant Accounting Policies [Line Items] |  |
Bank-owned life insurance, death benefits received | $ 312,000 | $ 102,000
Minimum |  |
Nature Of Banking Activities And Significant Accounting Policies [Line Items] |  |
Period of time between issuance of a loan commitment and closing and sale of the loan | 30 days |
Management's policy on evaluation of impairment | $ 250,000 |
Company not considered value of impairment on individual consumer, residential and small commercial loans | $ 250,000 |
Minimum | Software |  |
Nature Of Banking Activities And Significant Accounting Policies [Line Items] |  |
Estimated useful lives | 3 years |
Minimum | Core Deposits |  |
Nature Of Banking Activities And Significant Accounting Policies [Line Items] |  |
Intangible assets, estimated useful lives | 6 years |
Minimum | Premises and Equipment |  |
Nature Of Banking Activities And Significant Accounting Policies [Line Items] |  |
Estimated useful lives | 3 years |
Maximum |  |
Nature Of Banking Activities And Significant Accounting Policies [Line Items] |  |
Period of time between issuance of a loan commitment and closing and sale of the loan | 60 days |
Maximum | Software |  |
Nature Of Banking Activities And Significant Accounting Policies [Line Items] |  |
Estimated useful lives | 7 years |
Maximum | Core Deposits |  |
Nature Of Banking Activities And Significant Accounting Policies [Line Items] |  |
Intangible assets, estimated useful lives | 9 years |
Maximum | Premises and Equipment |  |
Nature Of Banking Activities And Significant Accounting Policies [Line Items] |  |
Estimated useful lives | 40 years |
Retained Earnings |  |
Nature Of Banking Activities And Significant Accounting Policies [Line Items] |  |
Reclassification of tax effects stranded in accumulated other comprehensive loss by tax rate change | $ 158,000 |
Accumulated Other Comprehensive Loss |  |
Nature Of Banking Activities And Significant Accounting Policies [Line Items] |  |
Reclassification of tax effects stranded in accumulated other comprehensive loss by tax rate change | (158,000) |
ASU 2018-02 | Retained Earnings |  |
Nature Of Banking Activities And Significant Accounting Policies [Line Items] |  |
Reclassification of tax effects stranded in accumulated other comprehensive loss by tax rate change | 158,000 |
ASU 2018-02 | Accumulated Other Comprehensive Loss |  |
Nature Of Banking Activities And Significant Accounting Policies [Line Items] |  |
Reclassification of tax effects stranded in accumulated other comprehensive loss by tax rate change | $ (158,000) |

X
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