Summary of significant accounting policies - Adoption of new accounting standard (Details) - USD ($) $ in Thousands	Mar. 31, 2023	Jan. 01, 2023	Dec. 31, 2022	Mar. 31, 2022	Dec. 31, 2021
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for credit losses	$ 25,444		$ 27,472	$ 28,407	$ 28,383
Stockholders' equity	328,634		315,350	$ 320,461	$ 340,126
Accrued interest receivable on loans	9,800
Accrued interest receivable on available of sale securities	1,600
Accrued interest receivable on held to maturity securities	191
Cumulative impact of adoption | ASU 2016-13
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for credit losses		$ 3,000	$ (3,263)
Stockholders' equity	$ 2,364	$ 2,400