Portfolio loans - Loans identified as impaired, segregated by category (Details) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2020	Dec. 31, 2019
Loans identified as impaired
Unpaid Contractual Principal Balance	$ 30,365	$ 45,686
Recorded Investment with No Allowance	15,421	29,540
Recorded Investment with Allowance	6,273	7,539
Total Recorded Investment	21,694	37,079
Related Allowance	2,404	4,853
Average Recorded Investment	30,150	45,370
Collateral dependent loans secured by real estate or business assets	17,500
Commercial Loans
Loans identified as impaired
Unpaid Contractual Principal Balance	15,464	14,415
Recorded Investment with No Allowance	2,554	4,727
Recorded Investment with Allowance	5,205	5,026
Total Recorded Investment	7,759	9,753
Related Allowance	1,694	3,330
Average Recorded Investment	8,746	13,774
Commercial Real Estate Loans
Loans identified as impaired
Unpaid Contractual Principal Balance	9,047	14,487
Recorded Investment with No Allowance	7,737	9,883
Recorded Investment with Allowance	594	2,039
Total Recorded Investment	8,331	11,922
Related Allowance	236	1,049
Average Recorded Investment	11,613	16,678
Real Estate Construction
Loans identified as impaired
Unpaid Contractual Principal Balance	569	1,116
Recorded Investment with No Allowance	552	974
Total Recorded Investment	552	974
Average Recorded Investment	709	873
Retail Real Estate
Loans identified as impaired
Unpaid Contractual Principal Balance	5,285	15,581
Recorded Investment with No Allowance	4,578	13,898
Recorded Investment with Allowance	474	474
Total Recorded Investment	5,052	14,372
Related Allowance	474	474
Average Recorded Investment	9,059	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	$ 23	$ 42