Portfolio loans and allowance for credit losses - Risk grades of portfolio loans by origination year (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Loans
Ending balance	$ 6,814,177	$ 6,687,249
Pass
Loans
Ending balance	6,016,748	5,997,126
Watch
Loans
Ending balance	554,970	413,876
Special Mention
Loans
Ending balance	150,481	181,107
Substandard
Loans
Ending balance	69,048	75,215
Substandard Non-accrual
Loans
Ending balance	22,930	27,896
Commercial
Loans
2020	843,404
2019	190,061
2018	127,410
2017	118,185
2016	72,647
Prior	105,947
Revolving loans	556,922
Ending balance	2,014,576
Commercial \| Pass
Loans
2020	812,536
2019	158,307
2018	107,565
2017	93,190
2016	61,847
Prior	79,970
Revolving loans	455,340
Ending balance	1,768,755	1,458,416
Commercial \| Watch
Loans
2020	16,544
2019	22,247
2018	14,954
2017	13,724
2016	2,577
Prior	10,943
Revolving loans	55,959
Ending balance	136,948	172,526
Commercial \| Special Mention
Loans
2020	6,402
2019	2,671
2018	2,069
2017	7,164
2016	6,763
Prior	13,733
Revolving loans	33,645
Ending balance	72,447	66,337
Commercial \| Substandard
Loans
2020	7,772
2019	3,791
2018	2,371
2017	1,939
2016	819
Prior	1,233
Revolving loans	9,978
Ending balance	27,903	41,273
Commercial \| Substandard Non-accrual
Loans
2020	150
2019	3,045
2018	451
2017	2,168
2016	641
Prior	68
Revolving loans	2,000
Ending balance	8,523	9,096
Commercial real estate
Loans
2020	840,882
2019	628,303
2018	463,787
2017	437,776
2016	222,941
Prior	278,923
Revolving loans	19,923
Ending balance	2,892,535
Commercial real estate \| Pass
Loans
2020	717,559
2019	503,977
2018	360,573
2017	384,843
2016	180,555
Prior	227,068
Revolving loans	18,797
Ending balance	2,393,372	2,477,398
Commercial real estate \| Watch
Loans
2020	88,297
2019	110,526
2018	90,412
2017	33,734
2016	32,887
Prior	27,023
Revolving loans	398
Ending balance	383,277	186,963
Commercial real estate \| Special Mention
Loans
2020	16,490
2019	8,858
2018	10,490
2017	10,505
2016	7,102
Prior	21,808
Revolving loans	233
Ending balance	75,486	105,487
Commercial real estate \| Substandard
Loans
2020	17,445
2019	4,166
2018	1,491
2017	7,812
2016	2,111
Prior	1,377
Revolving loans	495
Ending balance	34,897	26,204
Commercial real estate \| Substandard Non-accrual
Loans
2020	1,091
2019	776
2018	821
2017	882
2016	286
Prior	1,647
Ending balance	5,503	9,178
Real estate construction
Loans
2020	200,184
2019	175,330
2018	64,362
2017	3,306
2016	1,071
Prior	1,445
Revolving loans	16,088
Ending balance	461,786
Real estate construction \| Pass
Loans
2020	179,232
2019	171,663
2018	64,025
2017	1,468
2016	761
Prior	1,444
Revolving loans	16,088
Ending balance	434,681	351,923
Real estate construction \| Watch
Loans
2020	18,485
2019	3,657
2018	337
2017	1,838
2016	164
Ending balance	24,481	45,262
Real estate construction \| Special Mention
Loans
2020	67
2019	10
Ending balance	77	3,928
Real estate construction \| Substandard
Loans
2020	2,400
2016	146
Ending balance	2,546	737
Real estate construction \| Substandard Non-accrual
Loans
Prior	1
Ending balance	1	630
Retail Real Estate
Loans
2020	324,112
2019	164,938
2018	137,163
2017	137,949
2016	144,101
Prior	263,826
Revolving loans	235,763
Ending balance	1,407,852
Retail Real Estate \| Pass
Loans
2020	319,302
2019	162,711
2018	135,065
2017	136,427
2016	140,600
Prior	257,147
Revolving loans	231,364
Ending balance	1,382,616	1,661,691
Retail Real Estate \| Watch
Loans
2020	2,715
2019	2,053
2018	1,396
2017	349
2016	579
Prior	233
Revolving loans	2,939
Ending balance	10,264	9,125
Retail Real Estate \| Special Mention
Loans
2020	509
2016	1,962
Ending balance	2,471	5,355
Retail Real Estate \| Substandard
Loans
2020	899
2019	96
2018	56
2017	26
2016	727
Prior	1,631
Revolving loans	267
Ending balance	3,702	7,001
Retail Real Estate \| Substandard Non-accrual
Loans
2020	687
2019	78
2018	646
2017	1,147
2016	233
Prior	4,815
Revolving loans	1,193
Ending balance	8,799	8,935
Retail Other
Loans
2020	8,371
2019	9,437
2018	5,605
2017	2,531
2016	696
Prior	497
Revolving loans	10,291
Ending balance	37,428
Retail Other \| Pass
Loans
2020	8,357
2019	9,430
2018	5,600
2017	2,516
2016	691
Prior	440
Revolving loans	10,290
Ending balance	37,324	47,698
Retail Other \| Substandard Non-accrual
Loans
2020	14
2019	7
2018	5
2017	15
2016	5
Prior	57
Revolving loans	1
Ending balance	104	57
Commercial Loans
Loans
Ending balance	2,014,576	1,748,368
Commercial Real Estate Loans
Loans
Ending balance	2,892,535	2,793,417
Real Estate Construction
Loans
Ending balance	461,786	401,861
Retail Real Estate
Loans
Ending balance	1,407,852	1,693,769
Retail Other
Loans
Ending balance	$ 37,428	$ 49,834

Amount, before allowance for credit loss, of right to consideration from customer for product sold and service rendered in normal course of business.

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