Bank segment - Allowance for loan commitments (Details) - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2022	Mar. 31, 2021
Allowance for loan commitments:
Beginning balance	$ 4,900	$ 4,300
Provision	500	(1,400)
Ending balance	5,400	2,900
Real estate \| Home equity line of credit
Allowance for loan commitments:
Beginning balance	400	300
Provision	0	100
Ending balance	400	400
Real estate \| Commercial construction
Allowance for loan commitments:
Beginning balance	3,700	3,000
Provision	(100)	(1,700)
Ending balance	3,600	1,300
Commercial
Allowance for loan commitments:
Beginning balance	800	1,000
Provision	600	200
Ending balance	$ 1,400	$ 1,200

Amount of expected credit loss for credit exposure on off-balance-sheet commitment, including but not limited to, loan commitment, standby letter of credit, financial guarantee not accounted for as insurance. Excludes off-balance sheet credit exposure accounted for as insurance and instrument accounted for under derivatives and hedging.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 460
-SubTopic 10
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=121611286&loc=d3e11927-110247

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 20
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=124255206&loc=SL82919202-210446

Name:	us-gaap_OffBalanceSheetCreditLossLiability
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant