Portfolio Loans - Summary of risk grades segregated by category (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Loans
Portfolio loans	$ 6,779,300	$ 6,814,177
Pass
Loans
Portfolio loans	5,981,995	6,016,748
Watch
Loans
Portfolio loans	560,431	554,970
Special Mention
Loans
Portfolio loans	149,831	150,481
Substandard
Loans
Portfolio loans	65,337	69,048
Substandard Non-accrual
Loans
Portfolio loans	21,706	22,930
Commercial
Loans
Portfolio loans	2,067,371	2,014,576
Commercial | Pass
Loans
Portfolio loans	1,830,063	1,768,755
Commercial | Watch
Loans
Portfolio loans	123,390	136,948
Commercial | Special Mention
Loans
Portfolio loans	78,546	72,447
Commercial | Substandard
Loans
Portfolio loans	27,423	27,903
Commercial | Substandard Non-accrual
Loans
Portfolio loans	7,949	8,523
Commercial real estate
Loans
Portfolio loans	2,912,966	2,892,535
Commercial real estate | Pass
Loans
Portfolio loans	2,400,446	2,393,372
Commercial real estate | Watch
Loans
Portfolio loans	407,244	383,277
Commercial real estate | Special Mention
Loans
Portfolio loans	68,900	75,486
Commercial real estate | Substandard
Loans
Portfolio loans	31,212	34,897
Commercial real estate | Substandard Non-accrual
Loans
Portfolio loans	5,164	5,503
Real estate construction
Loans
Portfolio loans	422,633	461,786
Real estate construction | Pass
Loans
Portfolio loans	400,306	434,681
Real estate construction | Watch
Loans
Portfolio loans	19,918	24,481
Real estate construction | Special Mention
Loans
Portfolio loans	9	77
Real estate construction | Substandard
Loans
Portfolio loans	2,400	2,546
Real estate construction | Substandard Non-accrual
Loans
Portfolio loans		1
Retail Real Estate
Loans
Portfolio loans	1,343,299	1,407,852
Retail Real Estate | Pass
Loans
Portfolio loans	1,318,247	1,382,616
Retail Real Estate | Watch
Loans
Portfolio loans	9,879	10,264
Retail Real Estate | Special Mention
Loans
Portfolio loans	2,376	2,471
Retail Real Estate | Substandard
Loans
Portfolio loans	4,302	3,702
Retail Real Estate | Substandard Non-accrual
Loans
Portfolio loans	8,495	8,799
Retail Other
Loans
Portfolio loans	33,031	37,428
Retail Other | Pass
Loans
Portfolio loans	32,933	37,324
Retail Other | Substandard Non-accrual
Loans
Portfolio loans	98	104
Commercial Loans
Loans
Portfolio loans	2,067,371	2,014,576
Commercial Real Estate Loans
Loans
Portfolio loans	2,912,966	2,892,535
Real Estate Construction
Loans
Portfolio loans	422,633	461,786
Retail Real Estate
Loans
Portfolio loans	1,343,299	1,407,852
Retail Other
Loans
Portfolio loans	$ 33,031	$ 37,428