Derivatives and hedging activities - Fair Values of Derivative Instruments on the Balance Sheet (Details)	12 Months Ended
	Dec. 31, 2022 USD ($)	Dec. 31, 2023 USD ($) security
Derivatives, Fair Value
Asset Derivatives	$ 22,196,000	$ 19,833,000
Liability Derivatives	21,466,000	20,633,000
Cash collateral	14,530,000	17,590,000
Net Amounts of Assets presented in the Balance Sheet	21,466,000	20,633,000
Interest income
Derivatives, Fair Value
Amount of gain or (loss) reclassified as a increase to interest income	276,000
Interest rate swaps
Derivatives, Fair Value
Asset Derivatives	21,794,000	19,278,000
Interest rate floor
Derivatives, Fair Value
Asset Derivatives	1,000
Credit-risk contract
Derivatives, Fair Value
Cash collateral	0	2,500,000
Net Amounts of Assets presented in the Balance Sheet	2,000.0	2,700,000
Derivatives designated as hedging instruments | Other Assets.
Derivatives, Fair Value
Asset Derivatives	1,000
Derivatives designated as hedging instruments | Other Liabilities.
Derivatives, Fair Value
Liability Derivatives		1,270,000
Derivatives designated as hedging instruments | Interest rate products | Other Assets.
Derivatives, Fair Value
Notional amount		150,000,000
Asset Derivatives	1,000
Derivatives designated as hedging instruments | Interest rate products | Other Liabilities.
Derivatives, Fair Value
Liability Derivatives		1,270,000
Derivatives not designated as hedging instruments | Other Assets.
Derivatives, Fair Value
Asset Derivatives	22,195,000	19,836,000
Derivatives not designated as hedging instruments | Other Liabilities.
Derivatives, Fair Value
Liability Derivatives	21,466,000	19,364,000
Derivatives not designated as hedging instruments | Interest rate products
Derivatives, Fair Value
Notional amount		230,323,000
Derivatives not designated as hedging instruments | Interest rate products | Other Assets.
Derivatives, Fair Value
Asset Derivatives	22,195,000	19,833,000
Derivatives not designated as hedging instruments | Interest rate products | Other Liabilities.
Derivatives, Fair Value
Notional amount		230,323,000
Liability Derivatives	21,466,000	19,364,000
Derivatives not designated as hedging instruments | Other
Derivatives, Fair Value
Notional amount		8,403,000
Derivatives not designated as hedging instruments | Other | Other Assets.
Derivatives, Fair Value
Asset Derivatives		3,000
Derivatives not designated as hedging instruments | Other | Other Liabilities.
Derivatives, Fair Value
Notional amount		$ 7,408,000
Derivatives not designated as hedging instruments | Risk participation agreements
Derivatives, Fair Value
Notional amount	1,500,000
Derivatives not designated as hedging instruments | Interest rate swaps
Derivatives, Fair Value
Number of instruments held | security		109
Notional amount	187,300,000	$ 476,500,000
Derivatives not designated as hedging instruments | Interest rate floor
Derivatives, Fair Value
Notional amount	$ 25,000,000.0