Borrowings and Borrowing Capacity - Additional Information (Details) - USD ($)	1 Months Ended	12 Months Ended
Sep. 30, 2016	Dec. 31, 2017	Dec. 31, 2016
Debt Instrument [Line Items]
Federal funds purchased		$ 0	$ 0
Unsecured federal funds line of credit		137,500,000
Subordinated notes, carrying values		48,828,000	48,734,000
Junior subordinated debentures		38,623,000	32,740,000
Fixed-to-Floating Rate Subordinated Notes due 2026
Debt Instrument [Line Items]
Subordinated notes issued	$ 50,000,000
Initial interest rate	6.50%
Subordinated notes, carrying values		48,828,000	$ 48,734,000
Issuance costs of notes		$ 1,324,000
Notes underwriting discount percentage		1.50%
Notes underwriting discount amount		$ 750,000
Fixed-to-Floating Rate Subordinated Notes due 2026 \| London Interbank Offered Rate (LIBOR)
Debt Instrument [Line Items]
Description of floating rate basis		three-month LIBOR
Interest Rate	5.345%

Debt underwriting discount amount.

No definition available.

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- Definition

Debt underwriting discount percentage.

+ References

No definition available.

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- Definition

Subordinate notes interest rate.

+ References

No definition available.

+ Details

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- Definition

Percentage points added to the reference rate to compute the variable rate on the debt instrument.

+ References

No definition available.

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- Definition

The reference rate for the variable rate of the debt instrument, such as LIBOR or the US Treasury rate and the maturity of the reference rate used, such as three months or six months LIBOR.

+ References

No definition available.

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- Definition

Face (par) amount of debt instrument at time of issuance.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 55
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=64930739&loc=d3e28878-108400

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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

Amount, after accumulated amortization, of debt issuance costs. Includes, but is not limited to, legal, accounting, underwriting, printing, and registration costs.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
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- Definition

Amount of short term borrowing where a bank borrows, at the federal funds rate, from another bank.

+ References

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-Publisher FASB
-Name Accounting Standards Codification
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- Definition

Including the current and noncurrent portions, the carrying value of junior subordinated long-term debt owed to unconsolidated subsidiary trusts as of the balance sheet date. Such debt places a lender in a lien position behind debt having a higher priority of repayment in liquidation of the entity's assets and was initially scheduled to be repaid after one year or beyond the normal operating cycle if longer.

+ References

+ Details

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- Definition

Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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-Subparagraph (SX 210.5-02.19(b),22(b))
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- Definition

Including the current and noncurrent portions, carrying value as of the balance sheet date of subordinated debt (with initial maturities beyond one year or beyond the operating cycle if longer). Subordinated debt places a lender in a lien position behind debt having a higher priority of repayment in liquidation of the entity's assets.

+ References

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-Publisher FASB
-Name Accounting Standards Codification
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