Loans and allowance for credit losses - Additional Information (Details) - USD ($)			1 Months Ended	3 Months Ended		6 Months Ended		12 Months Ended
	Mar. 22, 2020	Feb. 14, 2020	Mar. 31, 2020	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019
Financing Receivable, Past Due [Line Items]
Accrued interest receivable				$ 23,009,000		$ 23,009,000
Carrying value of PCI loans								$ 57,152,000
Accretion of interest income						2,554,000	$ 3,928,000
Recorded investment in troubled debt restructurings				13,277,000		13,277,000		12,206,000
Allocation to specific reserves				606,000		606,000		360,000
Non-accrual loans				5,821,000		5,821,000		5,201,000
Payment default for loans modified as troubled debt restructurings				0	$ 0	$ 0	0
Classification of TDR, exemption period, CARES ACT	60 days
Payment deferral period						90 days
Minimum
Financing Receivable, Past Due [Line Items]
Payment deferral period			60 days
Maximum
Financing Receivable, Past Due [Line Items]
Payment deferral period			90 days
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					1,705,000		3,888,000
Total accretion excluded interest income					$ 2,097,000		$ 3,928,000
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				1,492,666,000		$ 1,492,666,000		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				501,728,000		501,728,000		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				$ 567,515,000		$ 567,515,000		$ 545,540,000
Farmers National
Financing Receivable, Past Due [Line Items]
Financing receivable, allowance for credit loss, acquisition		$ 4,494,000