Summary of significant accounting policies - Nature of operations and Basis of presentation (Details) $ in Thousands	12 Months Ended
Dec. 31, 2020 USD ($) Office
Summary of significant accounting policies
Number of full-service community banking offices \| Office	26
Reclassification of prior period items amounts effect on net income \| $	$ 0

The amount of a reclassification adjustment made to prior period financial statement amounts.

No definition available.

Name:	us-gaap_PriorPeriodReclassificationAdjustment
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration