Loan Portfolio and Credit Quality - Loans by Past Due Status (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Financing Receivable, Past Due [Line Items]
Accruing Past Due	$ 7,249	$ 19,862
Nonaccrual Loans	25,764	23,851
Current Accruing Loans	7,183,312	7,060,596
Net loans	7,216,325	7,104,309
Commercial and industrial
Financing Receivable, Past Due [Line Items]
Accruing Past Due	2,914	2,359
Nonaccrual Loans	4,766	4,394
Current Accruing Loans	660,537	551,590
Net loans	668,217	558,343
Paycheck Protection Program
Financing Receivable, Past Due [Line Items]
Accruing Past Due	0	0
Nonaccrual Loans	0	0
Current Accruing Loans	351,170	312,356
Net loans	351,170	312,356
Commercial tax-exempt
Financing Receivable, Past Due [Line Items]
Accruing Past Due	0	0
Nonaccrual Loans	0	0
Current Accruing Loans	488,507	442,159
Net loans	488,507	442,159
Commercial real estate
Financing Receivable, Past Due [Line Items]
Accruing Past Due	0	627
Nonaccrual Loans	5,859	5,261
Current Accruing Loans	2,691,818	2,751,487
Net loans	2,697,677	2,757,375
Construction and land
Financing Receivable, Past Due [Line Items]
Accruing Past Due	0	0
Nonaccrual Loans	0	0
Current Accruing Loans	181,482	159,204
Net loans	181,482	159,204
Residential
Financing Receivable, Past Due [Line Items]
Accruing Past Due	4,044	15,498
Nonaccrual Loans	14,475	13,780
Current Accruing Loans	2,614,035	2,648,186
Net loans	2,632,554	2,677,464
Home equity
Financing Receivable, Past Due [Line Items]
Accruing Past Due	104	1,363
Nonaccrual Loans	651	415
Current Accruing Loans	70,997	75,586
Net loans	71,752	77,364
Consumer and other
Financing Receivable, Past Due [Line Items]
Accruing Past Due	187	15
Nonaccrual Loans	13	1
Current Accruing Loans	124,766	120,028
Net loans	124,966	120,044
30-59 Days Past Due
Financing Receivable, Past Due [Line Items]
Accruing Past Due	7,235	14,055
30-59 Days Past Due | Commercial and industrial
Financing Receivable, Past Due [Line Items]
Accruing Past Due	2,914	1,837
30-59 Days Past Due | Paycheck Protection Program
Financing Receivable, Past Due [Line Items]
Accruing Past Due	0	0
30-59 Days Past Due | Commercial tax-exempt
Financing Receivable, Past Due [Line Items]
Accruing Past Due	0	0
30-59 Days Past Due | Commercial real estate
Financing Receivable, Past Due [Line Items]
Accruing Past Due	0	136
30-59 Days Past Due | Construction and land
Financing Receivable, Past Due [Line Items]
Accruing Past Due	0	0
30-59 Days Past Due | Residential
Financing Receivable, Past Due [Line Items]
Accruing Past Due	4,044	10,960
30-59 Days Past Due | Home equity
Financing Receivable, Past Due [Line Items]
Accruing Past Due	104	1,107
30-59 Days Past Due | Consumer and other
Financing Receivable, Past Due [Line Items]
Accruing Past Due	173	15
60-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Accruing Past Due	14	5,807
60-89 Days Past Due | Commercial and industrial
Financing Receivable, Past Due [Line Items]
Accruing Past Due	0	522
60-89 Days Past Due | Paycheck Protection Program
Financing Receivable, Past Due [Line Items]
Accruing Past Due	0	0
60-89 Days Past Due | Commercial tax-exempt
Financing Receivable, Past Due [Line Items]
Accruing Past Due	0	0
60-89 Days Past Due | Commercial real estate
Financing Receivable, Past Due [Line Items]
Accruing Past Due	0	491
60-89 Days Past Due | Construction and land
Financing Receivable, Past Due [Line Items]
Accruing Past Due	0	0
60-89 Days Past Due | Residential
Financing Receivable, Past Due [Line Items]
Accruing Past Due	0	4,538
60-89 Days Past Due | Home equity
Financing Receivable, Past Due [Line Items]
Accruing Past Due	0	256
60-89 Days Past Due | Consumer and other
Financing Receivable, Past Due [Line Items]
Accruing Past Due	14	0
Current
Financing Receivable, Past Due [Line Items]
Nonaccrual Loans	11,895	12,345
Current | Commercial and industrial
Financing Receivable, Past Due [Line Items]
Nonaccrual Loans	1,832	3,934
Current | Paycheck Protection Program
Financing Receivable, Past Due [Line Items]
Nonaccrual Loans	0	0
Current | Commercial tax-exempt
Financing Receivable, Past Due [Line Items]
Nonaccrual Loans	0	0
Current | Commercial real estate
Financing Receivable, Past Due [Line Items]
Nonaccrual Loans	601	0
Current | Construction and land
Financing Receivable, Past Due [Line Items]
Nonaccrual Loans	0	0
Current | Residential
Financing Receivable, Past Due [Line Items]
Nonaccrual Loans	8,838	8,183
Current | Home equity
Financing Receivable, Past Due [Line Items]
Nonaccrual Loans	611	228
Current | Consumer and other
Financing Receivable, Past Due [Line Items]
Nonaccrual Loans	13	0
30-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Nonaccrual Loans	3,569	1,609
30-89 Days Past Due | Commercial and industrial
Financing Receivable, Past Due [Line Items]
Nonaccrual Loans	1,914	87
30-89 Days Past Due | Paycheck Protection Program
Financing Receivable, Past Due [Line Items]
Nonaccrual Loans	0	0
30-89 Days Past Due | Commercial tax-exempt
Financing Receivable, Past Due [Line Items]
Nonaccrual Loans	0	0
30-89 Days Past Due | Commercial real estate
Financing Receivable, Past Due [Line Items]
Nonaccrual Loans	0	0
30-89 Days Past Due | Construction and land
Financing Receivable, Past Due [Line Items]
Nonaccrual Loans	0	0
30-89 Days Past Due | Residential
Financing Receivable, Past Due [Line Items]
Nonaccrual Loans	1,655	1,521
30-89 Days Past Due | Home equity
Financing Receivable, Past Due [Line Items]
Nonaccrual Loans	0	0
30-89 Days Past Due | Consumer and other
Financing Receivable, Past Due [Line Items]
Nonaccrual Loans	0	1
90 Days or Greater Past Due
Financing Receivable, Past Due [Line Items]
Nonaccrual Loans	10,300	9,897
90 Days or Greater Past Due | Commercial and industrial
Financing Receivable, Past Due [Line Items]
Nonaccrual Loans	1,020	373
90 Days or Greater Past Due | Paycheck Protection Program
Financing Receivable, Past Due [Line Items]
Nonaccrual Loans	0	0
90 Days or Greater Past Due | Commercial tax-exempt
Financing Receivable, Past Due [Line Items]
Nonaccrual Loans	0	0
90 Days or Greater Past Due | Commercial real estate
Financing Receivable, Past Due [Line Items]
Nonaccrual Loans	5,258	5,261
90 Days or Greater Past Due | Construction and land
Financing Receivable, Past Due [Line Items]
Nonaccrual Loans	0	0
90 Days or Greater Past Due | Residential
Financing Receivable, Past Due [Line Items]
Nonaccrual Loans	3,982	4,076
90 Days or Greater Past Due | Home equity
Financing Receivable, Past Due [Line Items]
Nonaccrual Loans	40	187
90 Days or Greater Past Due | Consumer and other
Financing Receivable, Past Due [Line Items]
Nonaccrual Loans	$ 0	$ 0