Loan Portfolio and Credit Quality Loans by Past Due Status (Details) $ in Thousands	Jun. 30, 2019 USD ($) loan	Dec. 31, 2018 USD ($) loan
Financing Receivable, Past Due [Line Items]
Accruing Past Due	$ 3,366	$ 22,299
Nonaccrual Loans	17,155	14,057
Current Accruing Loans	7,059,739	6,856,802
Total Loans Receivable	7,080,260	6,893,158
30-59 Days Past Due
Financing Receivable, Past Due [Line Items]
Accruing Past Due	2,100	16,540
60-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Accruing Past Due	334	5,759
Current
Financing Receivable, Past Due [Line Items]
Nonaccrual Loans	5,824	3,626
30-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Nonaccrual Loans	3,390	768
90 Days or Greater Past Due
Financing Receivable, Past Due [Line Items]
Nonaccrual Loans	7,941	9,663
Commercial and industrial
Financing Receivable, Past Due [Line Items]
Accruing Past Due	251	9,794
Nonaccrual Loans	1,567	2,554
Current Accruing Loans	654,368	610,689
Total Loans Receivable	656,186	623,037
Commercial and industrial | 30-59 Days Past Due
Financing Receivable, Past Due [Line Items]
Accruing Past Due	251	9,794
Commercial and industrial | 60-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Accruing Past Due	0	0
Commercial and industrial | Current
Financing Receivable, Past Due [Line Items]
Nonaccrual Loans	1,194	979
Commercial and industrial | 30-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Nonaccrual Loans	155	0
Commercial and industrial | 90 Days or Greater Past Due
Financing Receivable, Past Due [Line Items]
Nonaccrual Loans	218	1,575
Commercial tax-exempt
Financing Receivable, Past Due [Line Items]
Accruing Past Due	0	0
Nonaccrual Loans	0	0
Current Accruing Loans	450,307	451,671
Total Loans Receivable	450,307	451,671
Commercial tax-exempt | 30-59 Days Past Due
Financing Receivable, Past Due [Line Items]
Accruing Past Due	0	0
Commercial tax-exempt | 60-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Accruing Past Due	0	0
Commercial tax-exempt | Current
Financing Receivable, Past Due [Line Items]
Nonaccrual Loans	0	0
Commercial tax-exempt | 30-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Nonaccrual Loans	0	0
Commercial tax-exempt | 90 Days or Greater Past Due
Financing Receivable, Past Due [Line Items]
Nonaccrual Loans	0	0
Commercial real estate
Financing Receivable, Past Due [Line Items]
Accruing Past Due	982	0
Nonaccrual Loans	0	546
Current Accruing Loans	2,529,574	2,395,146
Total Loans Receivable	2,530,556	2,395,692
Commercial real estate | 30-59 Days Past Due
Financing Receivable, Past Due [Line Items]
Accruing Past Due	982	0
Commercial real estate | 60-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Accruing Past Due	0	0
Commercial real estate | Current
Financing Receivable, Past Due [Line Items]
Nonaccrual Loans	0	0
Commercial real estate | 30-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Nonaccrual Loans	0	0
Commercial real estate | 90 Days or Greater Past Due
Financing Receivable, Past Due [Line Items]
Nonaccrual Loans	0	546
Construction and land
Financing Receivable, Past Due [Line Items]
Accruing Past Due	0	0
Nonaccrual Loans	0	0
Current Accruing Loans	200,378	240,306
Total Loans Receivable	200,378	240,306
Construction and land | 30-59 Days Past Due
Financing Receivable, Past Due [Line Items]
Accruing Past Due	0	0
Construction and land | 60-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Accruing Past Due	0	0
Construction and land | Current
Financing Receivable, Past Due [Line Items]
Nonaccrual Loans	0	0
Construction and land | 30-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Nonaccrual Loans	0	0
Construction and land | 90 Days or Greater Past Due
Financing Receivable, Past Due [Line Items]
Nonaccrual Loans	0	0
Residential
Financing Receivable, Past Due [Line Items]
Accruing Past Due	1,266	6,843
Nonaccrual Loans	12,572	7,914
Current Accruing Loans	3,011,920	2,934,216
Total Loans Receivable	3,025,758	2,948,973
Residential | 30-59 Days Past Due
Financing Receivable, Past Due [Line Items]
Accruing Past Due	0	6,477
Residential | 60-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Accruing Past Due	334	366
Residential | Current
Financing Receivable, Past Due [Line Items]
Nonaccrual Loans	4,238	2,639
Residential | 30-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Nonaccrual Loans	2,961	716
Residential | 90 Days or Greater Past Due
Financing Receivable, Past Due [Line Items]
Accruing Past Due	900
Nonaccrual Loans	$ 5,373	$ 4,559
Number of loans | loan	1	0
Home equity
Financing Receivable, Past Due [Line Items]
Accruing Past Due	$ 0	$ 602
Nonaccrual Loans	3,004	3,031
Current Accruing Loans	86,926	86,788
Total Loans Receivable	89,930	90,421
Home equity | 30-59 Days Past Due
Financing Receivable, Past Due [Line Items]
Accruing Past Due	0	252
Home equity | 60-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Accruing Past Due	0	350
Home equity | Current
Financing Receivable, Past Due [Line Items]
Nonaccrual Loans	385	0
Home equity | 30-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Nonaccrual Loans	274	48
Home equity | 90 Days or Greater Past Due
Financing Receivable, Past Due [Line Items]
Nonaccrual Loans	2,345	2,983
Consumer and other
Financing Receivable, Past Due [Line Items]
Accruing Past Due	867	5,060
Nonaccrual Loans	12	12
Current Accruing Loans	126,266	137,986
Total Loans Receivable	127,145	143,058
Consumer and other | 30-59 Days Past Due
Financing Receivable, Past Due [Line Items]
Accruing Past Due	867	17
Consumer and other | 60-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Accruing Past Due	0	5,043
Consumer and other | Current
Financing Receivable, Past Due [Line Items]
Nonaccrual Loans	7	8
Consumer and other | 30-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Nonaccrual Loans	0	4
Consumer and other | 90 Days or Greater Past Due
Financing Receivable, Past Due [Line Items]
Nonaccrual Loans	$ 5	$ 0