Bank segment - Allowance for loan commitments (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020	Dec. 31, 2020	Dec. 31, 2019
Allowance for loan commitments:
Beginning balance	$ 2,900	$ 3,800	$ 4,300	$ 1,741	$ 1,741
Provision	750	4,300	(650)	4,800
Ending balance	3,650	8,100	3,650	8,100	$ 4,300	$ 1,741
Accounting standards update, extensible enumeration					us-gaap:AccountingStandardsUpdate201613Member	us-gaap:AccountingStandardsUpdate201613Member
Real estate | Home equity line of credit
Allowance for loan commitments:
Beginning balance	400	300	300	392	$ 392
Provision	0	0	100	0
Ending balance	400	300	400	300	300	$ 392
Real estate | Commercial construction
Allowance for loan commitments:
Beginning balance	1,300	3,191	3,000	931	931
Provision	1,100	4,309	(600)	4,824
Ending balance	2,400	7,500	2,400	7,500	3,000	931
Commercial
Allowance for loan commitments:
Beginning balance	1,200	309	1,000	418	418
Provision	(350)	(9)	(150)	(24)
Ending balance	$ 850	$ 300	$ 850	300	1,000	418
Impact of adoption of ASU No. 2016-13
Allowance for loan commitments:
Beginning balance				1,559	1,559
Ending balance						1,559
Impact of adoption of ASU No. 2016-13 | Real estate | Home equity line of credit
Allowance for loan commitments:
Beginning balance				(92)	(92)
Ending balance						(92)
Impact of adoption of ASU No. 2016-13 | Real estate | Commercial construction
Allowance for loan commitments:
Beginning balance				1,745	1,745
Ending balance						1,745
Impact of adoption of ASU No. 2016-13 | Commercial
Allowance for loan commitments:
Beginning balance				$ (94)	$ (94)
Ending balance						$ (94)