Allowance for Loan Losses - Age Analysis of Past Due Loans Segregated by Class of Loans (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	$ 5,890,141	$ 5,730,074
Past Due	58,878	35,860
Non- performing	46,073	23,938
Total Loans	5,949,019	5,765,934
Commercial real estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	2,903,997	2,681,395
Past Due	17,835	4,599
Non- performing	12,052	3,468
Total Loans	2,921,832	2,685,994
Commercial and industrial
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	1,482,473	1,426,754
Past Due	10,943	6,512
Non- performing	8,960	5,646
Total Loans	1,493,416	1,433,266
Commercial construction
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	243,004	377,968
Past Due	14,193	6,366
Non- performing	14,193	3,873
Total Loans	257,197	384,334
Residential mortgage
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	717,447	687,195
Past Due	9,232	11,579
Non- performing	7,128	7,165
Total Loans	726,679	698,774
Home equity
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	465,152	480,956
Past Due	6,410	6,370
Non- performing	3,698	3,715
Total Loans	471,562	487,326
Installment and other consumer
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	67,281	66,770
Past Due	265	434
Non- performing	42	71
Total Loans	67,546	67,204
Consumer construction
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	8,416	4,551
Past Due	0	0
Non- performing	0	0
Total Loans	8,416	4,551
Loans held for sale
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	2,371	4,485
Past Due	0	0
Non- performing	0	0
Total Loans	2,371	4,485
30-59 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	8,473	9,123
30-59 Days Past Due | Commercial real estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	3,638	997
30-59 Days Past Due | Commercial and industrial
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	1,000	420
30-59 Days Past Due | Commercial construction
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	0	2,473
30-59 Days Past Due | Residential mortgage
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	1,584	2,975
30-59 Days Past Due | Home equity
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	2,103	2,065
30-59 Days Past Due | Installment and other consumer
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	148	193
30-59 Days Past Due | Consumer construction
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	0	0
30-59 Days Past Due | Loans held for sale
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	0	0
60-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	4,332	2,799
60-89 Days Past Due | Commercial real estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	2,145	134
60-89 Days Past Due | Commercial and industrial
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	983	446
60-89 Days Past Due | Commercial construction
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	0	20
60-89 Days Past Due | Residential mortgage
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	520	1,439
60-89 Days Past Due | Home equity
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	609	590
60-89 Days Past Due | Installment and other consumer
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	75	170
60-89 Days Past Due | Consumer construction
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	0	0
60-89 Days Past Due | Loans held for sale
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	$ 0	$ 0