Loans, Allowance for Loan Losses and Credit Quality (Age Analysis of Past Due Financing Receivables) (Details) $ in Thousands		Sep. 30, 2019 USD ($) loan		Dec. 31, 2018 USD ($) loan
Age Analysis of Past Due Financing Receivables
Number of Loans 30-59 Days | loan		371		400
Number of Loans 60-89 Days | loan		31		56
Number of Loans 90 Days or More | loan		106		110
Number of Loans Total Past Due | loan		508		566
Principal Balance Total Past Due		$ 23,441		$ 46,348
Current		8,890,060		6,859,846
Total loans	[1]	8,913,501		6,906,194
Recorded Investment >90 Days and Accruing		$ 2,342		$ 5
Commercial and Industrial [Member]
Age Analysis of Past Due Financing Receivables
Number of Loans 30-59 Days | loan		1		0
Number of Loans 60-89 Days | loan		2		4
Number of Loans 90 Days or More | loan		3		11
Number of Loans Total Past Due | loan		6		15
Principal Balance Total Past Due		$ 417		$ 26,693
Current		1,411,099		1,066,936
Total loans	[1]	1,411,516		1,093,629
Recorded Investment >90 Days and Accruing		$ 0		$ 0
Commercial Real Estate [Member]
Age Analysis of Past Due Financing Receivables
Number of Loans 30-59 Days | loan		6		9
Number of Loans 60-89 Days | loan		2		0
Number of Loans 90 Days or More | loan		4		8
Number of Loans Total Past Due | loan		12		17
Principal Balance Total Past Due		$ 2,900		$ 3,877
Current		3,997,587		3,247,371
Total loans	[1]	4,000,487		3,251,248
Recorded Investment >90 Days and Accruing		$ 0		$ 0
Construction Loans [Member]
Age Analysis of Past Due Financing Receivables
Number of Loans 30-59 Days | loan		0		1
Number of Loans 60-89 Days | loan		0		0
Number of Loans 90 Days or More | loan		0		1
Number of Loans Total Past Due | loan		0		2
Principal Balance Total Past Due		$ 0		$ 1,582
Current		520,585		363,583
Total loans	[1]	520,585		365,165
Recorded Investment >90 Days and Accruing		$ 0		$ 0
Small Business [Member]
Age Analysis of Past Due Financing Receivables
Number of Loans 30-59 Days | loan		10		15
Number of Loans 60-89 Days | loan		5		19
Number of Loans 90 Days or More | loan		7		24
Number of Loans Total Past Due | loan		22		58
Principal Balance Total Past Due		$ 674		$ 755
Current		171,364		163,921
Total loans	[1]	172,038		164,676
Recorded Investment >90 Days and Accruing		$ 0		$ 0
Residential Real Estate [Member]
Age Analysis of Past Due Financing Receivables
Number of Loans 30-59 Days | loan		24		23
Number of Loans 60-89 Days | loan		6		6
Number of Loans 90 Days or More | loan		40		25
Number of Loans Total Past Due | loan		70		54
Principal Balance Total Past Due		$ 12,841		$ 8,389
Current		1,631,917		914,905
Total loans	[1]	1,644,758		923,294
Recorded Investment >90 Days and Accruing		$ 1,807	[2]	$ 0
Consumer Home Equity [Member]
Age Analysis of Past Due Financing Receivables
Number of Loans 30-59 Days | loan		23		22
Number of Loans 60-89 Days | loan		8		12
Number of Loans 90 Days or More | loan		36		29
Number of Loans Total Past Due | loan		67		63
Principal Balance Total Past Due		$ 6,270		$ 4,849
Current		1,130,839		1,087,235
Total loans	[1]	1,137,109		1,092,084
Recorded Investment >90 Days and Accruing		$ 511	[2]	$ 0
Consumer - Other [Member]
Age Analysis of Past Due Financing Receivables
Number of Loans 30-59 Days | loan	[3]	307		330
Number of Loans 60-89 Days | loan	[3]	8		15
Number of Loans 90 Days or More | loan	[3]	16		12
Number of Loans Total Past Due | loan	[3]	331		357
Principal Balance Total Past Due	[3]	$ 339		$ 203
Current	[3]	26,669		15,895
Total loans	[1],[3]	27,008		16,098
Recorded Investment >90 Days and Accruing	[3]	24		5
Financial Asset, 30 to 59 Days Past Due [Member]
Age Analysis of Past Due Financing Receivables
Principal Balance Total Past Due		7,708		8,402
Financial Asset, 30 to 59 Days Past Due [Member] | Commercial and Industrial [Member]
Age Analysis of Past Due Financing Receivables
Principal Balance Total Past Due		278		0
Financial Asset, 30 to 59 Days Past Due [Member] | Commercial Real Estate [Member]
Age Analysis of Past Due Financing Receivables
Principal Balance Total Past Due		1,641		1,627
Financial Asset, 30 to 59 Days Past Due [Member] | Construction Loans [Member]
Age Analysis of Past Due Financing Receivables
Principal Balance Total Past Due		0		1,271
Financial Asset, 30 to 59 Days Past Due [Member] | Small Business [Member]
Age Analysis of Past Due Financing Receivables
Principal Balance Total Past Due		315		506
Financial Asset, 30 to 59 Days Past Due [Member] | Residential Real Estate [Member]
Age Analysis of Past Due Financing Receivables
Principal Balance Total Past Due		3,267		3,486
Financial Asset, 30 to 59 Days Past Due [Member] | Consumer Home Equity [Member]
Age Analysis of Past Due Financing Receivables
Principal Balance Total Past Due		1,974		1,331
Financial Asset, 30 to 59 Days Past Due [Member] | Consumer - Other [Member]
Age Analysis of Past Due Financing Receivables
Principal Balance Total Past Due	[3]	233		181
Financial Asset, 60 to 89 Days Past Due [Member]
Age Analysis of Past Due Financing Receivables
Principal Balance Total Past Due		2,881		1,854
Financial Asset, 60 to 89 Days Past Due [Member] | Commercial and Industrial [Member]
Age Analysis of Past Due Financing Receivables
Principal Balance Total Past Due		100		382
Financial Asset, 60 to 89 Days Past Due [Member] | Commercial Real Estate [Member]
Age Analysis of Past Due Financing Receivables
Principal Balance Total Past Due		238		0
Financial Asset, 60 to 89 Days Past Due [Member] | Construction Loans [Member]
Age Analysis of Past Due Financing Receivables
Principal Balance Total Past Due		0		0
Financial Asset, 60 to 89 Days Past Due [Member] | Small Business [Member]
Age Analysis of Past Due Financing Receivables
Principal Balance Total Past Due		260		87
Financial Asset, 60 to 89 Days Past Due [Member] | Residential Real Estate [Member]
Age Analysis of Past Due Financing Receivables
Principal Balance Total Past Due		1,257		521
Financial Asset, 60 to 89 Days Past Due [Member] | Consumer Home Equity [Member]
Age Analysis of Past Due Financing Receivables
Principal Balance Total Past Due		982		855
Financial Asset, 60 to 89 Days Past Due [Member] | Consumer - Other [Member]
Age Analysis of Past Due Financing Receivables
Principal Balance Total Past Due	[3]	44		9
Financial Asset, Equal to or Greater than 90 Days Past Due [Member]
Age Analysis of Past Due Financing Receivables
Principal Balance Total Past Due		12,852		36,092
Financial Asset, Equal to or Greater than 90 Days Past Due [Member] | Commercial and Industrial [Member]
Age Analysis of Past Due Financing Receivables
Principal Balance Total Past Due		39		26,311
Financial Asset, Equal to or Greater than 90 Days Past Due [Member] | Commercial Real Estate [Member]
Age Analysis of Past Due Financing Receivables
Principal Balance Total Past Due		1,021		2,250
Financial Asset, Equal to or Greater than 90 Days Past Due [Member] | Construction Loans [Member]
Age Analysis of Past Due Financing Receivables
Principal Balance Total Past Due		0		311
Financial Asset, Equal to or Greater than 90 Days Past Due [Member] | Small Business [Member]
Age Analysis of Past Due Financing Receivables
Principal Balance Total Past Due		99		162
Financial Asset, Equal to or Greater than 90 Days Past Due [Member] | Residential Real Estate [Member]
Age Analysis of Past Due Financing Receivables
Principal Balance Total Past Due		8,317		4,382
Financial Asset, Equal to or Greater than 90 Days Past Due [Member] | Consumer Home Equity [Member]
Age Analysis of Past Due Financing Receivables
Principal Balance Total Past Due		3,314		2,663
Financial Asset, Equal to or Greater than 90 Days Past Due [Member] | Consumer - Other [Member]
Age Analysis of Past Due Financing Receivables
Principal Balance Total Past Due	[3]	$ 62		$ 13

[1] The amount of net deferred costs on originated loans included in the ending balance was $7.2 million and $7.1 million at September 30, 2019 and December 31, 2018, respectively. Net unamortized discounts on acquired loans not deemed to be purchased credit impaired ("PCI") included in the ending balance was $24.7 million and $15.2 million at September 30, 2019 and December 31, 2018, respectively.

[2] (1) Represents purchased credit impaired loans that are accruing interest due to expectations of future cash collections.

[3] (2) Other consumer portfolio is inclusive of deposit account overdrafts recorded as loan balances.