Portfolio loans - Past due loans (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Loans past due, still accruing
Loans past due, still accruing	$ 1,142		$ 1,142		$ 2,741
Non-accrual Loans	25,215		25,215		24,624
Gross interest income that would have been recorded if impaired loans had been current	300	$ 200	$ 700	$ 500
Restructured loan included in non-performing loans			90 days
Restructured loans:
Total loans	10,852		$ 10,852		11,900
30 to 59 Days
Loans past due, still accruing
Loans past due, still accruing	8,365		8,365		8,477
60 to 89 Days
Loans past due, still accruing
Loans past due, still accruing	1,652		1,652		4,420
In compliance with modified terms
Restructured loans:
Total loans	9,096		9,096		9,873
30-89 days past due
Restructured loans:
Total loans	22		22		108
Included in non-performing loans
Restructured loans:
Total loans	1,734		1,734		1,919
Commercial
Loans past due, still accruing
Loans past due, still accruing					1,808
Non-accrual Loans	9,135		9,135		5,285
Commercial | 30 to 59 Days
Loans past due, still accruing
Loans past due, still accruing	122		122		1,615
Commercial | 60 to 89 Days
Loans past due, still accruing
Loans past due, still accruing					323
Commercial real estate
Loans past due, still accruing
Loans past due, still accruing	750		750
Non-accrual Loans	8,597		8,597		11,997
Commercial real estate | 30 to 59 Days
Loans past due, still accruing
Loans past due, still accruing	1,504		1,504		1,856
Commercial real estate | 60 to 89 Days
Loans past due, still accruing
Loans past due, still accruing	349		349		2,737
Real estate construction
Loans past due, still accruing
Non-accrual Loans	23		23		608
Real estate construction | 30 to 59 Days
Loans past due, still accruing
Loans past due, still accruing	599		599
Real estate construction | 60 to 89 Days
Loans past due, still accruing
Loans past due, still accruing	123		123
Retail real estate
Loans past due, still accruing
Loans past due, still accruing	390		390		933
Non-accrual Loans	7,385		7,385		6,714
Retail real estate | 30 to 59 Days
Loans past due, still accruing
Loans past due, still accruing	6,093		6,093		4,840
Retail real estate | 60 to 89 Days
Loans past due, still accruing
Loans past due, still accruing	1,177		1,177		1,355
Retail other
Loans past due, still accruing
Loans past due, still accruing	2		2
Non-accrual Loans	75		75		20
Retail other | 30 to 59 Days
Loans past due, still accruing
Loans past due, still accruing	47		47		166
Retail other | 60 to 89 Days
Loans past due, still accruing
Loans past due, still accruing	$ 3		$ 3		$ 5