Bank segment - Allowance for loan commitments (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Allowance for loan commitments:
Beginning balance	$ 3,650	$ 8,100	$ 4,300	$ 1,741
Provision	250	(500)	(400)	4,300
Ending balance	3,900	7,600	3,900	7,600
Real estate | Home equity line of credit
Allowance for loan commitments:
Beginning balance	400	300	300	392
Provision	0	0	100	0
Ending balance	400	300	400	300
Real estate | Commercial construction
Allowance for loan commitments:
Beginning balance	2,400	7,500	3,000	931
Provision	300	(800)	(300)	4,024
Ending balance	2,700	6,700	2,700	6,700
Commercial
Allowance for loan commitments:
Beginning balance	850	300	1,000	418
Provision	(50)	300	(200)	276
Ending balance	$ 800	$ 600	$ 800	600
Impact of adoption of ASU No. 2016-13
Allowance for loan commitments:
Beginning 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)
Impact of adoption of ASU No. 2016-13 | Real estate | Commercial construction
Allowance for loan commitments:
Beginning balance				1,745
Impact of adoption of ASU No. 2016-13 | Commercial
Allowance for loan commitments:
Beginning balance				$ (94)