Allowance For Loan Losses - Past Due and Non-Accrual Loans (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Schedule of Aging of Financing Receivables [Line Items]
Gross loans	$ 2,687,228	$ 2,568,562
Total Past Due Loans	23,448	19,490
Current Loans	2,663,780	2,549,072
Non-accrual loans	$ 15,801	$ 14,771
The ratio of non-accrual loans to total loans	0.59%	0.58%
Commercial real estate
Schedule of Aging of Financing Receivables [Line Items]
Gross loans	$ 1,442,150	$ 1,394,179
Total Past Due Loans	12,838	9,541
Current Loans	1,429,312	1,384,638
Non-accrual loans	8,605	8,280
Commercial and industrial
Schedule of Aging of Financing Receivables [Line Items]
Gross loans	537,790	501,227
Total Past Due Loans	2,343	1,875
Current Loans	535,447	499,352
Non-accrual loans	2,942	3,285
Commercial construction
Schedule of Aging of Financing Receivables [Line Items]
Gross loans	345,683	317,477
Total Past Due Loans	6,142	5,636
Current Loans	339,541	311,841
Non-accrual loans	2,831	1,735
Residential mortgages
Schedule of Aging of Financing Receivables [Line Items]
Gross loans	254,188	247,373
Total Past Due Loans	1,647	1,606
Current Loans	252,541	245,767
Non-accrual loans	394	411
Home equity
Schedule of Aging of Financing Receivables [Line Items]
Gross loans	97,223	98,252
Total Past Due Loans	437	814
Current Loans	96,786	97,438
Non-accrual loans	1,014	1,040
Consumer
Schedule of Aging of Financing Receivables [Line Items]
Gross loans	10,194	10,054
Total Past Due Loans	41	18
Current Loans	10,153	10,036
Non-accrual loans	15	20
Not Adversely Classified
Schedule of Aging of Financing Receivables [Line Items]
Gross loans	2,654,814	2,531,440
Non-accrual loans not adversely classified	59	84
Not Adversely Classified | Commercial real estate
Schedule of Aging of Financing Receivables [Line Items]
Gross loans	1,428,877	1,377,515
Not Adversely Classified | Commercial and industrial
Schedule of Aging of Financing Receivables [Line Items]
Gross loans	526,888	487,957
Not Adversely Classified | Commercial construction
Schedule of Aging of Financing Receivables [Line Items]
Gross loans	339,874	312,641
Not Adversely Classified | Residential mortgages
Schedule of Aging of Financing Receivables [Line Items]
Gross loans	252,389	245,548
Not Adversely Classified | Home equity
Schedule of Aging of Financing Receivables [Line Items]
Gross loans	96,658	97,797
Not Adversely Classified | Consumer
Schedule of Aging of Financing Receivables [Line Items]
Gross loans	10,128	9,982
Loans 30-59 Days Past Due
Schedule of Aging of Financing Receivables [Line Items]
Gross loans	13,970	3,978
Loans 30-59 Days Past Due | Commercial real estate
Schedule of Aging of Financing Receivables [Line Items]
Gross loans	8,687	1,469
Loans 30-59 Days Past Due | Commercial and industrial
Schedule of Aging of Financing Receivables [Line Items]
Gross loans	1,042	576
Loans 30-59 Days Past Due | Commercial construction
Schedule of Aging of Financing Receivables [Line Items]
Gross loans	2,591	576
Loans 30-59 Days Past Due | Residential mortgages
Schedule of Aging of Financing Receivables [Line Items]
Gross loans	1,346	700
Loans 30-59 Days Past Due | Home equity
Schedule of Aging of Financing Receivables [Line Items]
Gross loans	270	645
Loans 30-59 Days Past Due | Consumer
Schedule of Aging of Financing Receivables [Line Items]
Gross loans	34	12
Loans 60-89 Days Past Due
Schedule of Aging of Financing Receivables [Line Items]
Gross loans	1,714	8,556
Loans 60-89 Days Past Due | Commercial real estate
Schedule of Aging of Financing Receivables [Line Items]
Gross loans	265	3,914
Loans 60-89 Days Past Due | Commercial and industrial
Schedule of Aging of Financing Receivables [Line Items]
Gross loans	722	1,034
Loans 60-89 Days Past Due | Commercial construction
Schedule of Aging of Financing Receivables [Line Items]
Gross loans	720	3,325
Loans 60-89 Days Past Due | Residential mortgages
Schedule of Aging of Financing Receivables [Line Items]
Gross loans	0	283
Loans 60-89 Days Past Due | Home equity
Schedule of Aging of Financing Receivables [Line Items]
Gross loans	0	0
Loans 60-89 Days Past Due | Consumer
Schedule of Aging of Financing Receivables [Line Items]
Gross loans	7	0
Loans equal to or greater than 90 days past due
Schedule of Aging of Financing Receivables [Line Items]
Gross loans	7,764	6,956
Loans equal to or greater than 90 days past due | Commercial real estate
Schedule of Aging of Financing Receivables [Line Items]
Gross loans	3,886	4,158
Loans equal to or greater than 90 days past due | Commercial and industrial
Schedule of Aging of Financing Receivables [Line Items]
Gross loans	579	265
Loans equal to or greater than 90 days past due | Commercial construction
Schedule of Aging of Financing Receivables [Line Items]
Gross loans	2,831	1,735
Loans equal to or greater than 90 days past due | Residential mortgages
Schedule of Aging of Financing Receivables [Line Items]
Gross loans	301	623
Loans equal to or greater than 90 days past due | Home equity
Schedule of Aging of Financing Receivables [Line Items]
Gross loans	167	169
Loans equal to or greater than 90 days past due | Consumer
Schedule of Aging of Financing Receivables [Line Items]
Gross loans	$ 0	$ 6