Portfolio loans and allowance for loan losses - Analysis of loans past due and still accruing or non-accrual status (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Loans past due
Loans past due, still accruing	$ 1,611	$ 1,601
Non-accrual Loans	27,896	34,997
Amount of interest collected and recognized on a cash basis			$ 300
30 to 59 Days
Loans past due
Loans past due, still accruing	8,820	5,053
60 to 89 Days
Loans past due
Loans past due, still accruing	5,451	2,068
Commercial
Loans past due
Loans past due, still accruing	199	775
Non-accrual Loans	9,096	17,953
Commercial | 30 to 59 Days
Loans past due
Loans past due, still accruing	1,075	158
Commercial | 60 to 89 Days
Loans past due
Loans past due, still accruing	1,014	140
Commercial real estate
Loans past due
Loans past due, still accruing	584
Non-accrual Loans	9,178	10,298
Commercial real estate | 30 to 59 Days
Loans past due
Loans past due, still accruing	2,653	148
Commercial real estate | 60 to 89 Days
Loans past due
Loans past due, still accruing	3,121	558
Real estate construction
Loans past due
Loans past due, still accruing		58
Non-accrual Loans	630	18
Real estate construction | 30 to 59 Days
Loans past due
Loans past due, still accruing	19	121
Retail Real Estate
Loans past due
Loans past due, still accruing	828	766
Non-accrual Loans	8,935	6,698
Retail Real Estate | 30 to 59 Days
Loans past due
Loans past due, still accruing	5,021	4,578
Retail Real Estate | 60 to 89 Days
Loans past due
Loans past due, still accruing	1,248	1,368
Retail Other
Loans past due
Loans past due, still accruing		2
Non-accrual Loans	57	30
Retail Other | 30 to 59 Days
Loans past due
Loans past due, still accruing	52	48
Retail Other | 60 to 89 Days
Loans past due
Loans past due, still accruing	$ 68	$ 2