Loans and allowance for loan losses - Additional Information (Details) - USD ($)	3 Months Ended	12 Months Ended
Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Financing Receivable, Recorded Investment, Past Due [Line Items]
Carrying value of PCI loans	$ 62,564,000		$ 68,999,000
Accretion of interest income	1,831,000	$ 1,687,000
Non-accrual loans	2,568,000		2,703,000
Recorded investment in troubled debt restructurings	8,953,000		6,794,000
Allocation to specific reserves	63,000		63,000
Payment default for loans modified as troubled debt restructurings	0		0
Purchased Credit Impaired
Financing Receivable, Recorded Investment, Past Due [Line Items]
Carrying value of PCI loans	62,564,000		68,999,000
Purchase accounting liquidity discount	2,093,000		2,436,000
Purchase accounting non accretable credit discount	3,480,000		4,355,000
Accretion of interest income	2,183,000	2,201,000
Total purchase accounting contribution through accretion for purchased loans	1,831,000	$ 1,687,000
Non-accrual loans	0		0
Non-Purchased Credit Impaired
Financing Receivable, Recorded Investment, Past Due [Line Items]
Purchase accounting liquidity discount	1,907,000		2,197,000
Purchase accounting accretable credit discount	7,025,000		7,527,000
Federal Reserve
Financing Receivable, Recorded Investment, Past Due [Line Items]
Pledged loans to the Federal Reserve Bank	1,365,193,000		1,336,092,000
Residential Mortgage Loans \| Federal Home Loan Bank of Cincinnati
Financing Receivable, Recorded Investment, Past Due [Line Items]
Pledge loans for Federal Home Loan Bank Debt	681,154,000		618,976,000
Commercial Loan \| Federal Home Loan Bank of Cincinnati
Financing Receivable, Recorded Investment, Past Due [Line Items]
Pledge loans for Federal Home Loan Bank Debt	$ 439,831,000		$ 608,735,000

Financing receivable modifications recorded investment specific reserves.

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- Definition

Purchase Accounting Accretable Credit Discount

+ References

No definition available.

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- Definition

Purchase Accounting Liquidity Discount

+ References

No definition available.

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- Definition

Purchase Accounting Non Accretable Credit Discount

+ References

No definition available.

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- Definition

Fair value at acquisition of acquired loans accounted for as debt securities with evidence of deterioration of credit quality.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 30
-Section 50
-Paragraph 2
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- Definition

Amount of accretion recognized for the excess of a loan's cash flows expected to be collected over the investor's initial investment in acquired loans not accounted for as debt securities, with evidence of deterioration of credit quality.

+ References

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- Definition

The amount of the outstanding recorded investment related to financing receivables that have been modified by troubled debt restructurings.

+ References

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-Publisher FASB
-Name Accounting Standards Codification
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- Definition

Amount of investment related to financing receivables modified by troubled debt restructurings within the previous 12 months, for which there was a payment default.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
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-Topic 310
-SubTopic 10
-Section 50
-Paragraph 34
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- Definition

Recorded investment in financing receivables that are on nonaccrual status as of the balance sheet date.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
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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

The cash outflow for loan origination associated cost which is usually collected through escrow.

+ References

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
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- Definition

The sum of the carrying amounts, as of the date of the latest financial statement presented, of loans receivable which are owned but transferred to serve as collateral for the payment of related debt obligations, primarily secured borrowings and repurchase agreements, and for which the transferees are not permitted to sell or re-pledge them to an unrelated party.

+ References

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- Definition

The carrying amount, as of the date of the latest financial statement presented, of loans receivable which are owned but transferred to serve as collateral for the payment of FHLB debt obligations, and for which the transferee is not permitted to sell or re-pledge them to an unrelated party.

+ References

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