Bank segment - Allowance for loan commitments (Details) - USD ($) $ in Thousands		3 Months Ended	6 Months Ended	12 Months Ended
	Jan. 01, 2020	Jun. 30, 2020	Jun. 30, 2020	Dec. 31, 2019
Allowance for loan commitments:
Beginning balance	$ 1,741	$ 3,800	$ 1,741
Provision		4,300	4,800
Ending balance		8,100	$ 8,100	$ 1,741
Accounting Standards Update [Extensible List]	us-gaap:AccountingStandardsUpdate201613Member		us-gaap:AccountingStandardsUpdate201613Member	us-gaap:AccountingStandardsUpdate201613Member
Real estate | Home equity line of credit
Allowance for loan commitments:
Beginning balance	$ 392	300	$ 392
Provision		0	0
Ending balance		300	300	$ 392
Real estate | Commercial construction
Allowance for loan commitments:
Beginning balance	931	3,191	931
Provision		4,309	4,824
Ending balance		7,500	7,500	931
Commercial
Allowance for loan commitments:
Beginning balance	418	309	418
Provision		(9)	(24)
Ending balance		$ 300	300	418
Impact of ASU No. 2016-13
Allowance for loan commitments:
Beginning balance	1,559		1,559
Ending balance	2,000			1,559
Impact 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 ASU No. 2016-13 | Real estate | Commercial construction
Allowance for loan commitments:
Beginning balance	1,745		1,745
Ending balance				1,745
Impact of ASU No. 2016-13 | Commercial
Allowance for loan commitments:
Beginning balance	$ (94)		$ (94)
Ending balance				$ (94)