Loans and allowance for credit losses - Additional Information (Details) - USD ($)	3 Months Ended		12 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019
Financing Receivable, Past Due [Line Items]
Accrued interest receivable	$ 16,019,000
Carrying value of PCI loans			$ 57,152,000
Accretion of interest income	1,578,000	$ 1,831,000
Recorded investment in troubled debt restructurings	11,566,000		12,206,000
Allocation to specific reserves	143,000		360,000
Non-accrual loans	4,893,000		5,201,000
Payment default for loans modified as troubled debt restructurings	0	0
Deferral on loans, executed, principal balance	35,461,000
Purchased Credit Impaired
Financing Receivable, Past Due [Line Items]
Carrying value of PCI loans			57,152,000
Purchase accounting liquidity discount			292,000
Purchase accounting non accretable credit discount			3,537,000
Accretion of interest income		2,183,000
Total accretion excluded interest income		$ 1,831,000
Non-Purchased Credit Impaired
Financing Receivable, Past Due [Line Items]
Purchase accounting liquidity discount			3,924,000
Purchase accounting accretable credit discount			8,964,000
Federal Reserve
Financing Receivable, Past Due [Line Items]
Pledged loans to the Federal Reserve Bank	1,460,435,000		1,407,662,000
Residential Mortgage Loans | Federal Home Loan Bank of Cincinnati
Financing Receivable, Past Due [Line Items]
Pledge loans for Federal Home Loan Bank Debt	422,916,000		412,966,000
Commercial Loan | Federal Home Loan Bank of Cincinnati
Financing Receivable, Past Due [Line Items]
Pledge loans for Federal Home Loan Bank Debt	571,358,000		$ 545,540,000
Farmers National
Financing Receivable, Past Due [Line Items]
Financing receivable, allowance for credit loss, acquisition	$ 4,494,000