Loan Portfolio and Credit Quality Loans by Past Due Status (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Financing Receivable, Recorded Investment, Past Due [Line Items]
Accruing Past Due	$ 22,299	$ 25,048
Nonaccrual receivables	14,057	14,295
Current Accruing Loans	6,856,802	6,465,685
Total loans	6,893,158	6,505,028
Commercial and industrial
Financing Receivable, Recorded Investment, Past Due [Line Items]
Accruing Past Due	9,794	11,752
Nonaccrual receivables	2,554	748
Current Accruing Loans	610,689	508,492
Total loans	623,037	520,992
Commercial tax-exempt
Financing Receivable, Recorded Investment, Past Due [Line Items]
Accruing Past Due	0	0
Nonaccrual receivables	0	0
Current Accruing Loans	451,671	418,698
Total loans	451,671	418,698
Commercial real estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Accruing Past Due	0	4,043
Nonaccrual receivables	546	1,985
Current Accruing Loans	2,395,146	2,434,192
Total loans	2,395,692	2,440,220
Construction and land
Financing Receivable, Recorded Investment, Past Due [Line Items]
Accruing Past Due	0	0
Nonaccrual receivables	0	110
Current Accruing Loans	240,306	164,880
Total loans	240,306	164,990
Residential
Financing Receivable, Recorded Investment, Past Due [Line Items]
Accruing Past Due	6,843	8,874
Nonaccrual receivables	7,914	8,470
Current Accruing Loans	2,934,216	2,665,189
Total loans	2,948,973	2,682,533
Home equity
Financing Receivable, Recorded Investment, Past Due [Line Items]
Accruing Past Due	602	355
Nonaccrual receivables	3,031	2,840
Current Accruing Loans	86,788	96,763
Total loans	90,421	99,958
Consumer and other
Financing Receivable, Recorded Investment, Past Due [Line Items]
Accruing Past Due	5,060	24
Nonaccrual receivables	12	142
Current Accruing Loans	137,986	177,471
Total loans	143,058	177,637
30-59 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Accruing Past Due	16,540	22,564
30-59 Days Past Due | Commercial and industrial
Financing Receivable, Recorded Investment, Past Due [Line Items]
Accruing Past Due	9,794	10,903
30-59 Days Past Due | Commercial tax-exempt
Financing Receivable, Recorded Investment, Past Due [Line Items]
Accruing Past Due	0	0
30-59 Days Past Due | Commercial real estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Accruing Past Due	0	4,043
30-59 Days Past Due | Construction and land
Financing Receivable, Recorded Investment, Past Due [Line Items]
Accruing Past Due	0	0
30-59 Days Past Due | Residential
Financing Receivable, Recorded Investment, Past Due [Line Items]
Accruing Past Due	6,477	7,239
30-59 Days Past Due | Home equity
Financing Receivable, Recorded Investment, Past Due [Line Items]
Accruing Past Due	252	355
30-59 Days Past Due | Consumer and other
Financing Receivable, Recorded Investment, Past Due [Line Items]
Accruing Past Due	17	24
60-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Accruing Past Due	5,759	2,484
60-89 Days Past Due | Commercial and industrial
Financing Receivable, Recorded Investment, Past Due [Line Items]
Accruing Past Due	0	849
60-89 Days Past Due | Commercial tax-exempt
Financing Receivable, Recorded Investment, Past Due [Line Items]
Accruing Past Due	0	0
60-89 Days Past Due | Commercial real estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Accruing Past Due	0	0
60-89 Days Past Due | Construction and land
Financing Receivable, Recorded Investment, Past Due [Line Items]
Accruing Past Due	0	0
60-89 Days Past Due | Residential
Financing Receivable, Recorded Investment, Past Due [Line Items]
Accruing Past Due	366	1,635
60-89 Days Past Due | Home equity
Financing Receivable, Recorded Investment, Past Due [Line Items]
Accruing Past Due	350	0
60-89 Days Past Due | Consumer and other
Financing Receivable, Recorded Investment, Past Due [Line Items]
Accruing Past Due	5,043	0
Current
Financing Receivable, Recorded Investment, Past Due [Line Items]
Nonaccrual receivables	3,626	1,340
Current | Commercial and industrial
Financing Receivable, Recorded Investment, Past Due [Line Items]
Nonaccrual receivables	979	355
Current | Commercial tax-exempt
Financing Receivable, Recorded Investment, Past Due [Line Items]
Nonaccrual receivables	0	0
Current | Commercial real estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Nonaccrual receivables	0	163
Current | Construction and land
Financing Receivable, Recorded Investment, Past Due [Line Items]
Nonaccrual receivables	0	0
Current | Residential
Financing Receivable, Recorded Investment, Past Due [Line Items]
Nonaccrual receivables	2,639	805
Current | Home equity
Financing Receivable, Recorded Investment, Past Due [Line Items]
Nonaccrual receivables	0	0
Current | Consumer and other
Financing Receivable, Recorded Investment, Past Due [Line Items]
Nonaccrual receivables	8	17
30-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Nonaccrual receivables	768	3,368
30-89 Days Past Due | Commercial and industrial
Financing Receivable, Recorded Investment, Past Due [Line Items]
Nonaccrual receivables	0	0
30-89 Days Past Due | Commercial tax-exempt
Financing Receivable, Recorded Investment, Past Due [Line Items]
Nonaccrual receivables	0	0
30-89 Days Past Due | Commercial real estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Nonaccrual receivables	0	0
30-89 Days Past Due | Construction and land
Financing Receivable, Recorded Investment, Past Due [Line Items]
Nonaccrual receivables	0	0
30-89 Days Past Due | Residential
Financing Receivable, Recorded Investment, Past Due [Line Items]
Nonaccrual receivables	716	3,172
30-89 Days Past Due | Home equity
Financing Receivable, Recorded Investment, Past Due [Line Items]
Nonaccrual receivables	48	71
30-89 Days Past Due | Consumer and other
Financing Receivable, Recorded Investment, Past Due [Line Items]
Nonaccrual receivables	4	125
90 Days or Greater Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Nonaccrual receivables	9,663	9,587
90 Days or Greater Past Due | Commercial and industrial
Financing Receivable, Recorded Investment, Past Due [Line Items]
Nonaccrual receivables	1,575	393
90 Days or Greater Past Due | Commercial tax-exempt
Financing Receivable, Recorded Investment, Past Due [Line Items]
Nonaccrual receivables	0	0
90 Days or Greater Past Due | Commercial real estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Nonaccrual receivables	546	1,822
90 Days or Greater Past Due | Construction and land
Financing Receivable, Recorded Investment, Past Due [Line Items]
Nonaccrual receivables	0	110
90 Days or Greater Past Due | Residential
Financing Receivable, Recorded Investment, Past Due [Line Items]
Nonaccrual receivables	4,559	4,493
90 Days or Greater Past Due | Home equity
Financing Receivable, Recorded Investment, Past Due [Line Items]
Nonaccrual receivables	2,983	2,769
90 Days or Greater Past Due | Consumer and other
Financing Receivable, Recorded Investment, Past Due [Line Items]
Nonaccrual receivables	$ 0	$ 0