Fair Values of Financial Instruments - Unobservable Inputs Used in Recurring and Nonrecurring Level 3 Fair Value Measurements Other Than Goodwill (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016
Discounted cash flow \| State and municipal securities
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair Value	$ 3,943	$ 5,134
Discounted cash flow \| State and municipal securities \| Minimum
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Maturity Call Date	1 month	1 month
US Muni BQ curve	A-	A-
Discount rate	0.69%	0.69%
Discounted cash flow \| State and municipal securities \| Maximum
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Maturity Call Date	20 years	20 years
US Muni BQ curve	BBB-	BBB-
Discount rate	5.00%	5.00%
Discounted cash flow \| Corporate obligations and Equity securities
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair Value	$ 35	$ 35
Discounted cash flow \| Corporate obligations and Equity securities \| Three-Month LIBOR
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Premium for illiquidity (percent)	2.00%	2.00%
Collateral based measurements \| Impaired loans (collateral dependent)
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair Value	$ 9,576	$ 15,318
Collateral based measurements \| Impaired loans (collateral dependent) \| Minimum
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Discount to reflect current market conditions and ultimate collectability (percent)	0.00%	0.00%
Collateral based measurements \| Impaired loans (collateral dependent) \| Maximum
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Discount to reflect current market conditions and ultimate collectability (percent)	10.00%	10.00%
Collateral based measurements \| Impaired loans (collateral dependent) \| Weighted Average
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Discount to reflect current market conditions and ultimate collectability (percent)	1.00%	1.00%
Appraisals \| Other real estate owned
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair Value	$ 859	$ 1,612
Appraisals \| Other real estate owned \| Minimum
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Discount to reflect current market conditions (percent)	0.00%	0.00%
Appraisals \| Other real estate owned \| Maximum
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Discount to reflect current market conditions (percent)	10.00%	10.00%
Appraisals \| Other real estate owned \| Weighted Average
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Discount to reflect current market conditions (percent)	2.00%	9.00%

Securities, Maturity

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- Definition

Fair value portion of probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=66048111&loc=d3e19207-110258

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- Definition

Description of the credit rating indicative of likelihood of repayment of the debt instrument given by a credit rating agency (for example, Standard and Poor's, Moody's, Fitch).

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=84159872&loc=d3e21475-112644

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(22))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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- Definition

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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- Definition

Risk-free interest rate assumption used in valuing an instrument.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (bbb)
-URI http://asc.fasb.org/extlink&oid=66048111&loc=d3e19207-110258

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- Definition

Adjustment to the discount rate used to measure fair value for lack of ability to convert business interests into cash quickly.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (bbb)
-URI http://asc.fasb.org/extlink&oid=66048111&loc=d3e19207-110258

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- Definition

Interest rate used to find the present value of an amount to be paid or received in the future as an input to measure fair value. For example, but not limited to, weighted average cost of capital (WACC), cost of capital, cost of equity and cost of debt.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (bbb)
-URI http://asc.fasb.org/extlink&oid=66048111&loc=d3e19207-110258

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- Definition

Rate at which loans or a loan portfolio are expected to prepay principal balances, used as an input to measure fair value.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (bbb)
-URI http://asc.fasb.org/extlink&oid=66048111&loc=d3e19207-110258

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