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Loans and Allowance for Loan Losses - Narrative (Details) | 6 Months Ended | 12 Months Ended |
--- | --- | --- | ---
Jun. 30, 2018 USD ($) loan segment | Dec. 31, 2017 USD ($) contract | Dec. 31, 2016 USD ($)
Financing Receivable, Modifications [Line Items] |  |  |
Loan portfolio segments | segment | 5 |  |
Allowance for loan losses | $ 7,073,937 | $ 5,860,291 | $ 5,105,000
Number of contracts | contract |  | 0 |
Foreclosed assets | 3,524,239 | $ 3,254,392 |
Trouble Debt Restructuring [Member] |  |  |
Financing Receivable, Modifications [Line Items] |  |  |
Loans that met criteria for restructured | $ 660,000 | $ 41,000 |
Number of contracts, nonaccrual | loan | 0 |  |
Residential Real Estate [Member] |  |  |
Financing Receivable, Modifications [Line Items] |  |  |
Foreclosed assets | $ 1,140,000 |  |
Commercial Real Estate [Member] |  |  |
Financing Receivable, Modifications [Line Items] |  |  |
Loans that met criteria for restructured | $ 622,000 |  |
Number of contracts | loan | 1 |  |

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