Loans and allowance for loan losses - Additional Information (Details) - USD ($)	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018
Financing Receivable, Recorded Investment, Past Due [Line Items]
Carrying value of PCI loans	$ 67,450,000		$ 67,450,000		$ 68,999,000
Accretion of interest income			3,928,000	$ 3,615,000
Non-accrual loans	2,448,000		2,448,000		2,703,000
Loans	4,289,516,000		4,289,516,000		3,667,511,000
Recorded investment in troubled debt restructurings	8,714,000		8,714,000		6,794,000
Allocation to specific reserves	50,000		50,000		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	67,450,000		67,450,000		68,999,000
Purchase accounting liquidity discount			1,605,000		2,436,000
Purchase accounting non accretable credit discount			4,596,000		4,355,000
Accretion of interest income	1,705,000	2,639,000	3,888,000	4,840,000
Total purchase accounting contribution through accretion for purchased loans	2,097,000	$ 1,928,000	3,928,000	$ 3,615,000
Non-accrual loans	0		0		0
Loans	67,450,000		67,450,000		68,999,000
Non-Purchased Credit Impaired
Financing Receivable, Recorded Investment, Past Due [Line Items]
Purchase accounting liquidity discount			4,740,000		2,197,000
Purchase accounting accretable credit discount			11,064,000		7,527,000
Federal Reserve
Financing Receivable, Recorded Investment, Past Due [Line Items]
Pledged loans to the Federal Reserve Bank	1,423,565,000		1,423,565,000		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	573,213,000		573,213,000		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	474,237,000		474,237,000		608,735,000
30-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans	11,195,000		11,195,000		9,208,000
30-89 Days Past Due | Purchased Credit Impaired
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans	5,541,000		5,541,000		3,605,000
90 Days or More and Accruing Interest
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans	2,100,000		2,100,000		3,041,000
90 Days or More and Accruing Interest | Purchased Credit Impaired
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans	$ 1,178,000		$ 1,178,000		$ 4,076,000