Fair value of financial instruments - Information about Significant Unobservable Inputs (Level 3) Used in Valuation of Assets Measured at Fair Value on Nonrecurring Basis (Details) - Non-recurring Basis $ in Thousands	Mar. 31, 2021 USD ($)	Dec. 31, 2020 USD ($)
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Collateral dependent loans	$ 47,430	$ 18,560
Other real estate owned	3,870	6,662
Significant unobservable inputs (level 3)
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Collateral dependent loans	47,430	18,560
Other real estate owned	$ 3,870	$ 6,662
Significant unobservable inputs (level 3) | Minimum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Collateral dependent loans, measurement input	0	0
Other real estate owned, measurement input	0	0
Significant unobservable inputs (level 3) | Maximum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Collateral dependent loans, measurement input	0.30	0.30
Other real estate owned, measurement input	0.15	0.15