Allowance for Loan Losses - Age Analysis of Past Due Loans Segregated by Class of Loans (Details) - USD ($) $ in Thousands	Dec. 31, 2019		Dec. 31, 2018
Financing Receivable, Past Due [Line Items]
Current	$ 7,060,617		$ 5,890,141
Past Due	81,791		58,878
Non- performing	54,057		46,073
Total Loans	7,142,408		5,949,019
Commercial real estate
Financing Receivable, Past Due [Line Items]
Current	3,376,156		2,903,997
Past Due	40,362		17,835
Non- performing	29,140		12,052
Total Loans	3,416,518		2,921,832
Commercial and industrial
Financing Receivable, Past Due [Line Items]
Current	1,700,522		1,482,473
Past Due	20,311		10,943
Non- performing	13,982		8,960
Total Loans	1,720,833		1,493,416
Commercial construction
Financing Receivable, Past Due [Line Items]
Current	372,589		243,004
Past Due	2,856		14,193
Non- performing	737		14,193
Total Loans	375,445		257,197
Residential mortgage
Financing Receivable, Past Due [Line Items]
Current	986,148		717,447
Past Due	12,437		9,232
Non- performing	7,519		7,128
Total Loans	998,585		726,679
Home equity
Financing Receivable, Past Due [Line Items]
Current	533,367		465,152
Past Due	4,981		6,410
Non- performing	2,639		3,698
Total Loans	538,348		471,562
Installment and other consumer
Financing Receivable, Past Due [Line Items]
Current	78,189		67,281
Past Due	844		265
Non- performing	40		42
Total Loans	79,033		67,546
Consumer construction
Financing Receivable, Past Due [Line Items]
Current	8,390		8,416
Past Due	0		0
Non- performing	0		0
Total Loans	8,390		8,416
Loans held for sale
Financing Receivable, Past Due [Line Items]
Current	5,256		2,371
Past Due	0		0
Non- performing	0		0
Total Loans	5,256		2,371
30-59 Days Past Due
Financing Receivable, Past Due [Line Items]
Past Due	17,992		8,473
30-59 Days Past Due | Commercial real estate
Financing Receivable, Past Due [Line Items]
Past Due	9,595		3,638
30-59 Days Past Due | Commercial and industrial
Financing Receivable, Past Due [Line Items]
Past Due	2,940		1,000
30-59 Days Past Due | Commercial construction
Financing Receivable, Past Due [Line Items]
Past Due	956		0
30-59 Days Past Due | Residential mortgage
Financing Receivable, Past Due [Line Items]
Past Due	2,016		1,584
30-59 Days Past Due | Home equity
Financing Receivable, Past Due [Line Items]
Past Due	2,059		2,103
30-59 Days Past Due | Installment and other consumer
Financing Receivable, Past Due [Line Items]
Past Due	426		148
30-59 Days Past Due | Consumer construction
Financing Receivable, Past Due [Line Items]
Past Due	0		0
30-59 Days Past Due | Loans held for sale
Financing Receivable, Past Due [Line Items]
Past Due	0		0
60-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Past Due	5,985		4,332
60-89 Days Past Due | Commercial real estate
Financing Receivable, Past Due [Line Items]
Past Due	716		2,145
60-89 Days Past Due | Commercial and industrial
Financing Receivable, Past Due [Line Items]
Past Due	1,946		983
60-89 Days Past Due | Commercial construction
Financing Receivable, Past Due [Line Items]
Past Due	1,163		0
60-89 Days Past Due | Residential mortgage
Financing Receivable, Past Due [Line Items]
Past Due	1,727		520
60-89 Days Past Due | Home equity
Financing Receivable, Past Due [Line Items]
Past Due	141		609
60-89 Days Past Due | Installment and other consumer
Financing Receivable, Past Due [Line Items]
Past Due	292		75
60-89 Days Past Due | Consumer construction
Financing Receivable, Past Due [Line Items]
Past Due	0		0
60-89 Days Past Due | Loans held for sale
Financing Receivable, Past Due [Line Items]
Past Due	0		0
90 Days Past Due
Financing Receivable, Past Due [Line Items]
Past Due	3,757	[1]	0
90 Days Past Due | Commercial real estate
Financing Receivable, Past Due [Line Items]
Past Due	911	[1]	0
90 Days Past Due | Commercial and industrial
Financing Receivable, Past Due [Line Items]
Past Due	1,443	[1]	0
90 Days Past Due | Commercial construction
Financing Receivable, Past Due [Line Items]
Past Due	0	[1]	0
90 Days Past Due | Residential mortgage
Financing Receivable, Past Due [Line Items]
Past Due	1,175	[1]	0
90 Days Past Due | Home equity
Financing Receivable, Past Due [Line Items]
Past Due	142	[1]	0
90 Days Past Due | Installment and other consumer
Financing Receivable, Past Due [Line Items]
Past Due	86	[1]	0
90 Days Past Due | Consumer construction
Financing Receivable, Past Due [Line Items]
Past Due	0	[1]	0
90 Days Past Due | Loans held for sale
Financing Receivable, Past Due [Line Items]
Past Due	$ 0	[1]	$ 0

[1] Represents acquired loans that were recorded at fair value at the acquisition date and remain performing.