Allowance Allocations (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance				$ 61,566				$ 55,825	$ 61,566	$ 55,825	$ 55,100
Charge-offs									(6,209)	(3,472)	(4,918)
Recoveries									2,336	3,138	4,143
Provision (benefit)	$ 1,300	$ 0	$ 1,050	600	$ 4,000	$ 950	$ 600	525	2,950	6,075	1,500
Ending balance	60,643				61,566				60,643	61,566	55,825
Ending balance: individually evaluated for impairment	1,342				5,214				1,342	5,214	1,930
Ending balance: collectively evaluated for impairment	59,301				56,352				59,301	56,352	53,895
Financing receivables ending balance:
Financing Receivable, Collectively Evaluated for Impairment	6,269,729				5,903,916				6,269,729	5,903,916	5,475,716
Individually evaluated for impairment	72,801				77,297				72,801	77,297	51,410
Financing Receivable, Net	4,539,256				4,355,968				4,539,256	4,355,968
Loans Receivable, Gross, Commercial and Industrial	888,528				902,053				888,528	902,053
Loans Receivable, Gross, Commercial, Mortgage	3,116,561				3,010,798				3,116,561	3,010,798
Total loans	6,355,553				5,999,605				6,355,553	5,999,605	5,547,721	[1]
Loans and Leases Receivable, Gross, Consumer, Other	9,880				11,064				9,880	11,064
Loans Receivable, Gross, Commercial, Construction	401,797				320,391				401,797	320,391
Small Business	132,370				122,726				132,370	122,726
Loans and Leases Receivable, Gross, Consumer, Mortgage	754,329				644,426				754,329	644,426
Commercial and Industrial [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance				16,921				13,802	16,921	13,802	15,573
Charge-offs									(3,891)	(593)	(2,010)
Recoveries									615	859	1,593
Provision (benefit)									(389)	2,853	(1,354)
Ending balance	13,256				16,921				13,256	16,921	13,802
Ending balance: individually evaluated for impairment	10				3,661				10	3,661	183
Ending balance: collectively evaluated for impairment	13,246				13,260				13,246	13,260	13,619
Financing receivables ending balance:
Financing Receivable, Collectively Evaluated for Impairment	853,885				862,875				853,885	862,875	838,129
Individually evaluated for impairment	34,643				39,178				34,643	39,178	5,147
Financing Receivable, Net	888,528				902,053				888,528	902,053
Total loans	888,528				902,053				888,528	902,053	843,276
Commercial Real Estate [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance				30,369				27,327	30,369	27,327	25,873
Charge-offs									(39)	(414)	(330)
Recoveries									385	564	1,073
Provision (benefit)									738	2,892	711
Ending balance	31,453				30,369				31,453	30,369	27,327
Ending balance: individually evaluated for impairment	42				196				42	196	204
Ending balance: collectively evaluated for impairment	31,411				30,173				31,411	30,173	27,123
Financing receivables ending balance:
Financing Receivable, Collectively Evaluated for Impairment	3,093,945				2,983,642				3,093,945	2,983,642	2,619,294
Individually evaluated for impairment	16,638				16,813				16,638	16,813	22,986
Financing Receivable, Net	3,116,561				3,010,798				3,116,561	3,010,798
Total loans	3,116,561				3,010,798				3,116,561	3,010,798	2,653,434
Construction Loans [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance				4,522				5,366	4,522	5,366	3,945
Charge-offs									0	0	0
Recoveries									0	0
Provision (benefit)									1,176	(844)	1,421
Ending balance	5,698				4,522				5,698	4,522	5,366
Ending balance: individually evaluated for impairment	0				0				0	0	0
Ending balance: collectively evaluated for impairment	5,698				4,522				5,698	4,522	5,366
Financing receivables ending balance:
Financing Receivable, Collectively Evaluated for Impairment	401,797				320,391				401,797	320,391	373,064
Individually evaluated for impairment	0				0				0	0	304
Financing Receivable, Net	401,797				320,391				401,797	320,391
Total loans	401,797				320,391				401,797	320,391	373,368
Small Business [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance				1,502				1,264	1,502	1,264	1,171
Charge-offs									(302)	(228)	(267)
Recoveries									114	195	264
Provision (benefit)									263	271	96
Ending balance	1,577				1,502				1,577	1,502	1,264
Ending balance: individually evaluated for impairment	1				8				1	8	4
Ending balance: collectively evaluated for impairment	1,576				1,494				1,576	1,494	1,260
Financing receivables ending balance:
Financing Receivable, Collectively Evaluated for Impairment	131,667				121,855				131,667	121,855	95,225
Individually evaluated for impairment	703				871				703	871	1,021
Financing Receivable, Net	132,370				122,726				132,370	122,726
Total loans	132,370				122,726				132,370	122,726	96,246
Residential Real Estate [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance				2,621				2,590	2,621	2,590	2,834
Charge-offs									(207)	(28)	(285)
Recoveries									31	299	133
Provision (benefit)									377	(240)	(92)
Ending balance	2,822				2,621				2,822	2,621	2,590
Ending balance: individually evaluated for impairment	1,007				1,086				1,007	1,086	1,278
Ending balance: collectively evaluated for impairment	1,815				1,535				1,815	1,535	1,312
Financing receivables ending balance:
Financing Receivable, Collectively Evaluated for Impairment	733,809				622,392				733,809	622,392	614,014
Individually evaluated for impairment	13,684				14,175				13,684	14,175	15,405
Total loans	754,329				644,426				754,329	644,426	638,606
Home Equity [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance				5,238				4,889	5,238	4,889	4,956
Charge-offs									(276)	(602)	(710)
Recoveries									198	141	356
Provision (benefit)									230	810	287
Ending balance	5,390				5,238				5,390	5,238	4,889
Ending balance: individually evaluated for impairment	265				242				265	242	238
Ending balance: collectively evaluated for impairment	5,125				4,996				5,125	4,996	4,651
Financing receivables ending balance:
Financing Receivable, Collectively Evaluated for Impairment	1,045,053				982,095				1,045,053	982,095	921,563
Individually evaluated for impairment	6,826				5,863				6,826	5,863	5,989
Total loans	1,052,088				988,147				1,052,088	988,147	927,803
Consumer Portfolio Segment [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance				$ 393				$ 587	393	587	748
Charge-offs									(1,494)	(1,607)	(1,316)
Recoveries									993	1,080	724
Provision (benefit)									555	333	431
Ending balance	447				393				447	393	587
Ending balance: individually evaluated for impairment	17				21				17	21	23
Ending balance: collectively evaluated for impairment	430				372				430	372	564
Financing receivables ending balance:
Financing Receivable, Collectively Evaluated for Impairment	9,573				10,666				9,573	10,666	14,427
Individually evaluated for impairment	307				397				307	397	558
Total loans	9,880				11,064				9,880	11,064	14,988
Receivables Acquired with Deteriorated Credit Quality [Member]
Financing receivables ending balance:
Financing Receivable, Net	13,023				18,392				13,023	18,392	20,595
Receivables Acquired with Deteriorated Credit Quality [Member] | Commercial and Industrial [Member]
Financing receivables ending balance:
Financing Receivable, Net	0				0				0	0	0
Receivables Acquired with Deteriorated Credit Quality [Member] | Commercial Real Estate [Member]
Financing receivables ending balance:
Financing Receivable, Net	5,978				10,343				5,978	10,343	11,154
Receivables Acquired with Deteriorated Credit Quality [Member] | Construction Loans [Member]
Financing receivables ending balance:
Financing Receivable, Net	0				0				0	0	0
Receivables Acquired with Deteriorated Credit Quality [Member] | Small Business [Member]
Financing receivables ending balance:
Financing Receivable, Net	0				0				0	0	0
Receivables Acquired with Deteriorated Credit Quality [Member] | Residential Real Estate [Member]
Financing receivables ending balance:
Financing Receivable, Net	6,836				7,859				6,836	7,859	9,187
Receivables Acquired with Deteriorated Credit Quality [Member] | Home Equity [Member]
Financing receivables ending balance:
Financing Receivable, Net	209				189				209	189	251
Receivables Acquired with Deteriorated Credit Quality [Member] | Consumer Portfolio Segment [Member]
Financing receivables ending balance:
Financing Receivable, Net	$ 0				$ 1				$ 0	$ 1	$ 3

[1] The amount of net deferred costs on originated loans included in the ending balance was $6.1 million, $5.1 million, and $4.3 million at December 31, 2017, 2016, and 2015, respectively. Net unamortized discounts on acquired loans not deemed to be PCI included in the ending balance was $9.4 million, $8.6 million, and $6.6 million at December 31, 2017, 2016, and 2015, respectively.