Summary of significant accounting policies - Nature of operations and Basis of presentation (Details)		3 Months Ended
Apr. 29, 2022 $ / shares	Mar. 31, 2022 Office $ / shares	Mar. 31, 2021 $ / shares
Summary of significant accounting policies
Number of full-service community banking offices \| Office		28
Dividends declared \| $ / shares	$ 0.39	$ 0.39	$ 0.37

Aggregate dividends declared during the period for each share of common stock outstanding.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.3-04)
-URI http://asc.fasb.org/extlink&oid=120397183&loc=d3e187085-122770

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Namespace Prefix:	us-gaap_
Data Type:	dtr-types:perShareItemType
Balance Type:	na
Period Type:	duration