Allowance Allocations (Details)	3 Months Ended								12 Months Ended
	Dec. 31, 2019 USD ($)	Sep. 30, 2019 USD ($)	Jun. 30, 2019 USD ($)	Mar. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Sep. 30, 2018 USD ($)	Jun. 30, 2018 USD ($)	Mar. 31, 2018 USD ($)	Dec. 31, 2019 USD ($) contract	Dec. 31, 2018 USD ($) contract	Dec. 31, 2017 USD ($) contract
Financing Receivable Impaired [Line Items]
Unamortized Loan Commitment and Origination fees	$ 7,100,000				$ 7,089,000				$ 7,100,000	$ 7,089,000	$ 6,100,000
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance				$ 64,293,000				$ 60,643,000	64,293,000	60,643,000	61,566,000
Charge-offs									(5,205,000)	(2,597,000)	(6,209,000)
Recoveries									2,652,000	1,472,000	2,336,000
Provision (benefit)	4,000,000	$ 0	$ 1,000,000	1,000,000	1,200,000	$ 1,075,000	$ 2,000,000	500,000	6,000,000	4,775,000	2,950,000
Ending balance	67,740,000				64,293,000				67,740,000	64,293,000	60,643,000
Ending balance: collectively evaluated for impairment	66,760,000				63,214,000				66,760,000	63,214,000	59,301,000
Ending balance: individually evaluated for impairment	980,000				1,079,000				980,000	1,079,000	1,342,000
Financing receivables ending balance:
Financing Receivable, Collectively Evaluated for Impairment	8,809,155,000				6,838,339,000				8,809,155,000	6,838,339,000	6,269,729,000
Individually evaluated for impairment	49,628,000				59,060,000				49,628,000	59,060,000	72,801,000
Financing Receivable, after Allowance for Credit Loss	6,119,185,000				4,874,718,000				6,119,185,000	4,874,718,000
Total loans	8,873,639,000				6,906,194,000				$ 8,873,639,000	$ 6,906,194,000	$ 6,355,553,000	[1]
Financing Receivable, Troubled Debt Restructuring, Subsequent Default, Number of Contracts | contract									0	0	1
Commercial and Industrial [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance				15,760,000				13,256,000	$ 15,760,000	$ 13,256,000	$ 16,921,000
Charge-offs									(244,000)	(355,000)	(3,891,000)
Recoveries									1,131,000	182,000	615,000
Provision (benefit)									947,000	2,677,000	(389,000)
Ending balance	17,594,000				15,760,000				17,594,000	15,760,000	13,256,000
Ending balance: collectively evaluated for impairment	17,468,000				15,753,000				17,468,000	15,753,000	13,246,000
Ending balance: individually evaluated for impairment	126,000				7,000				126,000	7,000	10,000
Financing receivables ending balance:
Financing Receivable, Collectively Evaluated for Impairment	1,370,580,000				1,064,800,000				1,370,580,000	1,064,800,000	853,885,000
Individually evaluated for impairment	24,456,000				28,829,000				24,456,000	28,829,000	34,643,000
Financing Receivable, after Allowance for Credit Loss	1,395,036,000				1,093,629,000				1,395,036,000	1,093,629,000
Total loans	1,395,036,000				1,093,629,000				1,395,036,000	1,093,629,000	$ 888,528,000
Financing Receivable, before Allowance for Credit Loss	1,395,036,000				1,093,629,000				1,395,036,000	1,093,629,000
Financing Receivable, Troubled Debt Restructuring, Subsequent Default, Number of Contracts											122,000
Commercial Real Estate [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance				32,370,000				31,453,000	32,370,000	31,453,000	$ 30,369,000
Charge-offs									(2,614,000)	(82,000)	(39,000)
Recoveries									152,000	188,000	385,000
Provision (benefit)									3,027,000	811,000	738,000
Ending balance	32,935,000				32,370,000				32,935,000	32,370,000	31,453,000
Ending balance: collectively evaluated for impairment	32,887,000				32,333,000				32,887,000	32,333,000	31,411,000
Ending balance: individually evaluated for impairment	48,000				37,000				48,000	37,000	42,000
Financing receivables ending balance:
Financing Receivable, Collectively Evaluated for Impairment	3,987,848,000				3,235,418,000				3,987,848,000	3,235,418,000	3,093,945,000
Individually evaluated for impairment	8,337,000				10,839,000				8,337,000	10,839,000	16,638,000
Financing Receivable, after Allowance for Credit Loss	4,002,359,000				3,251,248,000				4,002,359,000	3,251,248,000
Total loans	4,002,359,000				3,251,248,000				4,002,359,000	3,251,248,000	3,116,561,000
Financing Receivable, before Allowance for Credit Loss	4,002,359,000				3,251,248,000				4,002,359,000	3,251,248,000
Construction Loans [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance				5,158,000				5,698,000	5,158,000	5,698,000	4,522,000
Charge-offs									0	0	0
Recoveries									0	0	0
Provision (benefit)									895,000	(540,000)	1,176,000
Ending balance	6,053,000				5,158,000				6,053,000	5,158,000	5,698,000
Ending balance: collectively evaluated for impairment	6,053,000				5,158,000				6,053,000	5,158,000	5,698,000
Ending balance: individually evaluated for impairment	0				0				0	0
Financing receivables ending balance:
Financing Receivable, Collectively Evaluated for Impairment	547,293,000				365,165,000				547,293,000	365,165,000	401,797,000
Individually evaluated for impairment	0				0				0	0	0
Financing Receivable, after Allowance for Credit Loss	547,293,000				365,165,000				547,293,000	365,165,000
Total loans	547,293,000				365,165,000				547,293,000	365,165,000	401,797,000
Financing Receivable, before Allowance for Credit Loss	547,293,000				365,165,000				547,293,000	365,165,000
Small Business [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance				1,756,000				1,577,000	1,756,000	1,577,000	1,502,000
Charge-offs									(509,000)	(372,000)	(302,000)
Recoveries									122,000	46,000	114,000
Provision (benefit)									377,000	505,000	263,000
Ending balance	1,746,000				1,756,000				1,746,000	1,756,000	1,577,000
Ending balance: collectively evaluated for impairment	1,738,000				1,755,000				1,738,000	1,755,000	1,576,000
Ending balance: individually evaluated for impairment	8,000				1,000				8,000	1,000	1,000
Financing receivables ending balance:
Financing Receivable, Collectively Evaluated for Impairment	173,960,000				164,135,000				173,960,000	164,135,000	131,667,000
Individually evaluated for impairment	537,000				541,000				537,000	541,000	703,000
Financing Receivable, after Allowance for Credit Loss	174,497,000				164,676,000				174,497,000	164,676,000
Total loans	174,497,000				164,676,000				174,497,000	164,676,000	132,370,000
Financing Receivable, before Allowance for Credit Loss	174,497,000				164,676,000				174,497,000	164,676,000
Residential Real Estate [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance				3,219,000				2,822,000	3,219,000	2,822,000	2,621,000
Charge-offs									0	(148,000)	(207,000)
Recoveries									142,000	12,000	31,000
Provision (benefit)									79,000	533,000	377,000
Ending balance	3,440,000				3,219,000				3,440,000	3,219,000	2,822,000
Ending balance: collectively evaluated for impairment	2,803,000				2,357,000				2,803,000	2,357,000	1,815,000
Ending balance: individually evaluated for impairment	637,000				862,000				637,000	862,000	1,007,000
Financing receivables ending balance:
Financing Receivable, Collectively Evaluated for Impairment	1,571,848,000				906,959,000				1,571,848,000	906,959,000	733,809,000
Individually evaluated for impairment	11,228,000				12,706,000				11,228,000	12,706,000	13,684,000
Total loans	1,590,569,000				923,294,000				1,590,569,000	923,294,000	754,329,000
Financing Receivable, before Allowance for Credit Loss	1,590,569,000				923,294,000				1,590,569,000	923,294,000
Home Equity [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance				5,608,000				5,390,000	5,608,000	5,390,000	5,238,000
Charge-offs									(240,000)	(293,000)	(276,000)
Recoveries									318,000	156,000	198,000
Provision (benefit)									(110,000)	355,000	230,000
Ending balance	5,576,000				5,608,000				5,576,000	5,608,000	5,390,000
Ending balance: collectively evaluated for impairment	5,420,000				5,444,000				5,420,000	5,444,000	5,125,000
Ending balance: individually evaluated for impairment	156,000				164,000				156,000	164,000	265,000
Financing receivables ending balance:
Financing Receivable, Collectively Evaluated for Impairment	1,127,963,000				1,085,961,000				1,127,963,000	1,085,961,000	1,045,053,000
Individually evaluated for impairment	4,948,000				5,948,000				4,948,000	5,948,000	6,826,000
Total loans	1,133,798,000				1,092,084,000				1,133,798,000	1,092,084,000	1,052,088,000
Consumer Portfolio Segment [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance				$ 422,000				$ 447,000	422,000	447,000	393,000
Charge-offs									(1,598,000)	(1,347,000)	(1,494,000)
Recoveries									787,000	888,000	993,000
Provision (benefit)									785,000	434,000	555,000
Ending balance	396,000				422,000				396,000	422,000	447,000
Ending balance: collectively evaluated for impairment	391,000				414,000				391,000	414,000	430,000
Ending balance: individually evaluated for impairment	5,000				8,000				5,000	8,000	17,000
Financing receivables ending balance:
Financing Receivable, Collectively Evaluated for Impairment	29,663,000				15,901,000				29,663,000	15,901,000	9,573,000
Individually evaluated for impairment	122,000				197,000				122,000	197,000	307,000
Total loans	30,087,000				16,098,000				30,087,000	16,098,000	9,880,000
Financing Receivable, before Allowance for Credit Loss	30,087,000				16,098,000				30,087,000	16,098,000
Financial Asset Acquired with Credit Deterioration [Member]
Financing receivables ending balance:
Financing Receivable, after Allowance for Credit Loss	14,856,000				8,795,000				14,856,000	8,795,000	13,023,000
Financial Asset Acquired with Credit Deterioration [Member] | Commercial and Industrial [Member]
Financing receivables ending balance:
Financing Receivable, after Allowance for Credit Loss	0				0				0	0	0
Financial Asset Acquired with Credit Deterioration [Member] | Commercial Real Estate [Member]
Financing receivables ending balance:
Financing Receivable, after Allowance for Credit Loss	6,174,000				4,991,000				6,174,000	4,991,000	5,978,000
Financial Asset Acquired with Credit Deterioration [Member] | Construction Loans [Member]
Financing receivables ending balance:
Financing Receivable, after Allowance for Credit Loss	0				0				0	0	0
Financial Asset Acquired with Credit Deterioration [Member] | Small Business [Member]
Financing receivables ending balance:
Financing Receivable, after Allowance for Credit Loss	0				0				0	0	0
Financial Asset Acquired with Credit Deterioration [Member] | Residential Real Estate [Member]
Financing receivables ending balance:
Financing Receivable, after Allowance for Credit Loss	7,493,000				3,629,000				7,493,000	3,629,000	6,836,000
Financial Asset Acquired with Credit Deterioration [Member] | Home Equity [Member]
Financing receivables ending balance:
Financing Receivable, after Allowance for Credit Loss	887,000				175,000				887,000	175,000	209,000
Financial Asset Acquired with Credit Deterioration [Member] | Consumer Portfolio Segment [Member]
Financing receivables ending balance:
Financing Receivable, after Allowance for Credit Loss	$ 302,000				$ 0				$ 302,000	$ 0	$ 0

[1] The amount of net deferred costs on originated loans included in the ending balance was $7.1 million, at December 31, 2019 and 2018 and $6.1 million and at December 31, 2017. Net unamortized discounts on acquired loans not deemed to be PCI included in the ending balance were $21.6 million, $15.2 million and $9.4 million at December 31, 2019, 2018 and 2017, respectively.