Loans and Allowance for Loan Losses - Narrative (Details)	3 Months Ended	12 Months Ended
Mar. 31, 2018 USD ($) contract loan segment	Dec. 31, 2017 USD ($) contract	Dec. 31, 2016 USD ($)
Financing Receivable, Modifications [Line Items]
Loan portfolio segments \| segment	5
Allowance for loan losses	$ 6,477,000	$ 5,860,000	$ 5,105,000
Number of contracts \| contract	0	0
Foreclosed assets	$ 2,665,057	$ 3,254,392
Mortgage loans in process of foreclosure	201,000
Trouble Debt Restructuring [Member]
Financing Receivable, Modifications [Line Items]
Loans that met criteria for restructured	$ 40,000	$ 41,000
Number of contracts, nonaccrual \| loan	0
Residential Real Estate [Member]
Financing Receivable, Modifications [Line Items]
Foreclosed assets	$ 681,000

Financing Receivable, Nonaccrual, Number Of Contracts

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

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Number of financing receivables that have been modified by troubled debt restructurings.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 33
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The amount of the outstanding recorded investment related to financing receivables that have been modified by troubled debt restructurings.

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Carrying amount as of the balance sheet date of all assets obtained in full or partial satisfaction of a debt arrangement through foreclosure proceedings or defeasance; includes real and personal property; equity interests in corporations, partnerships, and joint ventures; and beneficial interests in trusts.

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- Definition

Amount of allowance to cover probable credit losses on loans and leases. Includes carryover of or adjustments to the allowance for loan losses in connection with business combinations. Excludes allowance for loans and leases covered under loss sharing agreements.

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- Definition

Recorded investment of consumer mortgage loan receivables secured by residential real estate properties for which formal foreclosure proceedings are in process.

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Number of segments reported by the entity. A reportable segment is a component of an entity for which there is an accounting requirement to report separate financial information on that component in the entity's financial statements.

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No definition available.

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