Portfolio loans - Loans identified as impaired, segregated by category (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2020	Dec. 31, 2019
Loans identified as impaired
Unpaid Contractual Principal Balance	$ 32,008	$ 45,686
Recorded Investment with No Allowance	20,021	29,540
Recorded Investment with Allowance	5,351	7,539
Total Recorded Investment	25,372	37,079
Related Allowance	3,938	4,853
Average Recorded Investment	40,408	45,370
Collateral dependent loans secured by real estate or business assets	13,500
Commercial Loans
Loans identified as impaired
Unpaid Contractual Principal Balance	11,795	14,415
Recorded Investment with No Allowance	3,751	4,727
Recorded Investment with Allowance	3,671	5,026
Total Recorded Investment	7,422	9,753
Related Allowance	2,822	3,330
Average Recorded Investment	11,493	13,774
Commercial Real Estate Loans
Loans identified as impaired
Unpaid Contractual Principal Balance	11,992	14,487
Recorded Investment with No Allowance	9,111	9,883
Recorded Investment with Allowance	1,206	2,039
Total Recorded Investment	10,317	11,922
Related Allowance	642	1,049
Average Recorded Investment	15,226	16,678
Real Estate Construction
Loans identified as impaired
Unpaid Contractual Principal Balance	579	1,116
Recorded Investment with No Allowance	562	974
Total Recorded Investment	562	974
Average Recorded Investment	888	873
Retail Real Estate
Loans identified as impaired
Unpaid Contractual Principal Balance	7,642	15,581
Recorded Investment with No Allowance	6,597	13,898
Recorded Investment with Allowance	474	474
Total Recorded Investment	7,071	14,372
Related Allowance	474	474
Average Recorded Investment	12,767	14,003
Retail Other
Loans identified as impaired
Unpaid Contractual Principal Balance		87
Recorded Investment with No Allowance		58
Total Recorded Investment		58
Average Recorded Investment	$ 34	$ 42