Loans and the Allowance for Loan Losses - Additional Information (Details)	3 Months Ended	6 Months Ended	12 Months Ended
Jun. 30, 2018 USD ($) Loan	Jun. 30, 2018 USD ($) Loan	Dec. 31, 2017 USD ($) Loan
Financing Receivable Modifications [Line Items]
Loans outstanding to directors and officers	$ 408,000	$ 408,000	$ 516,000
Loans to directors and officers, additions		8,000	124,000
Loans to directors and officers, repayments		116,000	298,000
Commitments to lend additional funds to borrowers whose loans were on non-accrual status	$ 0	$ 0	$ 0
Number of loans modified as troubled debt restructuring \| Loan	0	0	1
Number of loans determined to be troubled debt restructurings \| Loan		3	3
Troubled debt restructuring carrying value	$ 133,000	$ 133,000	$ 150,000
Number of TDRs defaulted during the period \| Loan		0	0
Pre-modification carrying value			$ 65,000
Post-modification carrying value			$ 48,000
Number of loans designated to be troubled debt restructurings \| Loan			2
Specific allowances for troubled debt restructurings	0	$ 0	$ 0
Loans secured by one- to-four family residential properties in process of foreclosure	$ 351,000,000	$ 351,000,000	64,000,000
Troubled Debt Restructurings
Financing Receivable Modifications [Line Items]
Troubled debt restructuring carrying value			$ 29,000

Financing receivable number of loans designated as troubled debt restructurings charged-off.

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Financing receivable number of loans determined to be troubled debt restructurings.

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Loans and leases receivable nonaccrual status commitment to lend.

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Loans secured by one to four family residential properties in process of foreclosure.

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Specific allowance for troubled debt restructurings.

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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.

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

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Post-modification amount of investment in financing receivables modified by troubled debt restructurings.

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Pre-modification amount of investment in financing receivables modified by troubled debt restructurings.

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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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Number of financing receivables that have been modified by troubled debt restructurings within the previous 12 months and for which there was a payment default.

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For an unclassified balance sheet, reflects the carrying amount of unpaid loan amounts due from related parties at the balance sheet date.

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Reflects the amount of new advances made to related parties in the form of loan and lease receivables.

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Amount of cash inflow from related parties which reduce the amount of loans and leases receivable due from related parties.

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