Loans and Leases - Allowance for Loan and Lease Losses by Method of Impairment (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016
Allowance on loans and leases:
Individually evaluated for impairment	$ 426		$ 258
Collectively evaluated for impairment	18,972		17,267
Allowance on loans and leases	19,398	$ 17,662	17,525	$ 16,399	$ 17,107	$ 17,486
Carrying value of loans and leases:
Individually evaluated for impairment	11,500		13,940
Collectively evaluated for impairment	3,350,400		3,241,069
Portfolio loans and leases	3,389,501		3,285,858
Purchased credit-impaired
Allowance on loans and leases:
Allowance on loans and leases	0		0
Carrying value of loans and leases:
Portfolio loans and leases	27,601		30,849
Originated
Allowance on loans and leases:
Individually evaluated for impairment	209		208
Collectively evaluated for impairment	18,972		17,267
Allowance on loans and leases	19,181		17,475
Carrying value of loans and leases:
Individually evaluated for impairment	7,883		8,878
Collectively evaluated for impairment	2,692,931		2,478,418
Portfolio loans and leases	2,700,814		2,487,296
Acquired
Carrying value of loans and leases:
Individually evaluated for impairment	3,617		5,062
Collectively evaluated for impairment	657,469		762,651
Portfolio loans and leases	688,687		798,562
Financial Asset Acquired With and Without Credit Deterioration
Allowance on loans and leases:
Individually evaluated for impairment	217		50
Collectively evaluated for impairment	0		0
Allowance on loans and leases	217		50
Commercial mortgage
Allowance on loans and leases:
Individually evaluated for impairment	0		0
Collectively evaluated for impairment	8,033		7,550
Allowance on loans and leases	8,033	7,174	7,550	6,608	6,410	6,227
Carrying value of loans and leases:
Individually evaluated for impairment	1,011		2,128
Collectively evaluated for impairment	1,603,381		1,503,825
Portfolio loans and leases	1,613,721		1,523,377
Commercial mortgage | Purchased credit-impaired
Allowance on loans and leases:
Allowance on loans and leases	0		0
Carrying value of loans and leases:
Portfolio loans and leases	9,329		17,424
Commercial mortgage | Originated
Allowance on loans and leases:
Individually evaluated for impairment	0		0
Collectively evaluated for impairment	8,033		7,550
Allowance on loans and leases	8,033		7,550
Carrying value of loans and leases:
Individually evaluated for impairment	0		1,345
Collectively evaluated for impairment	1,237,885		1,120,982
Portfolio loans and leases	1,237,885		1,122,327
Commercial mortgage | Acquired
Carrying value of loans and leases:
Individually evaluated for impairment	1,011		783
Collectively evaluated for impairment	365,496		382,843
Portfolio loans and leases	375,836		401,050
Commercial mortgage | Financial Asset Acquired With and Without Credit Deterioration
Allowance on loans and leases:
Individually evaluated for impairment	0		0
Collectively evaluated for impairment	0		0
Allowance on loans and leases	0		0
Home equity loans and lines
Allowance on loans and leases:
Individually evaluated for impairment	19		19
Collectively evaluated for impairment	914		1,067
Allowance on loans and leases	933	1,045	1,086	1,214	1,243	1,255
Carrying value of loans and leases:
Individually evaluated for impairment	2,995		2,162
Collectively evaluated for impairment	202,923		215,604
Portfolio loans and leases	206,429		218,275
Home equity loans and lines | Purchased credit-impaired
Allowance on loans and leases:
Allowance on loans and leases	0		0
Carrying value of loans and leases:
Portfolio loans and leases	511		509
Home equity loans and lines | Originated
Allowance on loans and leases:
Individually evaluated for impairment	19		19
Collectively evaluated for impairment	914		1,067
Allowance on loans and leases	933		1,086
Carrying value of loans and leases:
Individually evaluated for impairment	2,505		1,902
Collectively evaluated for impairment	174,266		181,381
Portfolio loans and leases	176,771		183,283
Home equity loans and lines | Acquired
Carrying value of loans and leases:
Individually evaluated for impairment	490		260
Collectively evaluated for impairment	28,657		34,223
Portfolio loans and leases	29,658		34,992
Home equity loans and lines | Financial Asset Acquired With and Without Credit Deterioration
Allowance on loans and leases:
Individually evaluated for impairment	0		0
Collectively evaluated for impairment	0		0
Allowance on loans and leases	0		0
Residential mortgage
Allowance on loans and leases:
Individually evaluated for impairment	299		230
Collectively evaluated for impairment	1,634		1,696
Allowance on loans and leases	1,933	1,898	1,926	1,776	1,798	1,917
Carrying value of loans and leases:
Individually evaluated for impairment	5,603		7,726
Collectively evaluated for impairment	443,457		451,160
Portfolio loans and leases	449,060		458,886
Residential mortgage | Purchased credit-impaired
Allowance on loans and leases:
Allowance on loans and leases	0		0
Carrying value of loans and leases:
Portfolio loans and leases	0		0
Residential mortgage | Originated
Allowance on loans and leases:
Individually evaluated for impairment	182		180
Collectively evaluated for impairment	1,634		1,696
Allowance on loans and leases	1,816		1,876
Carrying value of loans and leases:
Individually evaluated for impairment	3,974		4,418
Collectively evaluated for impairment	354,297		356,517
Portfolio loans and leases	358,271		360,935
Residential mortgage | Acquired
Carrying value of loans and leases:
Individually evaluated for impairment	1,629		3,308
Collectively evaluated for impairment	89,160		94,643
Portfolio loans and leases	90,789		97,951
Residential mortgage | Financial Asset Acquired With and Without Credit Deterioration
Allowance on loans and leases:
Individually evaluated for impairment	117		50
Collectively evaluated for impairment	0		0
Allowance on loans and leases	117		50
Construction
Allowance on loans and leases:
Individually evaluated for impairment	0		0
Collectively evaluated for impairment	1,158		937
Allowance on loans and leases	1,158	844	937	1,111	2,195	2,233
Carrying value of loans and leases:
Individually evaluated for impairment	0		0
Collectively evaluated for impairment	188,474		204,088
Portfolio loans and leases	190,874		212,454
Construction | Purchased credit-impaired
Allowance on loans and leases:
Allowance on loans and leases	0		0
Carrying value of loans and leases:
Portfolio loans and leases	2,400		8,366
Construction | Originated
Allowance on loans and leases:
Individually evaluated for impairment	0		0
Collectively evaluated for impairment	1,158		937
Allowance on loans and leases	1,158		937
Carrying value of loans and leases:
Individually evaluated for impairment	0		0
Collectively evaluated for impairment	147,636		128,266
Portfolio loans and leases	147,636		128,266
Construction | Acquired
Carrying value of loans and leases:
Individually evaluated for impairment	0		0
Collectively evaluated for impairment	40,838		75,822
Portfolio loans and leases	43,238		84,188
Construction | Financial Asset Acquired With and Without Credit Deterioration
Allowance on loans and leases:
Individually evaluated for impairment	0		0
Collectively evaluated for impairment	0		0
Allowance on loans and leases	0		0
Commercial and industrial
Allowance on loans and leases:
Individually evaluated for impairment	104		5
Collectively evaluated for impairment	5,568		5,033
Allowance on loans and leases	5,672	5,361	5,038	4,813	4,747	5,142
Carrying value of loans and leases:
Individually evaluated for impairment	1,864		1,897
Collectively evaluated for impairment	728,081		712,865
Portfolio loans and leases	745,306		719,312
Commercial and industrial | Purchased credit-impaired
Allowance on loans and leases:
Allowance on loans and leases	0		0
Carrying value of loans and leases:
Portfolio loans and leases	15,361		4,550
Commercial and industrial | Originated
Allowance on loans and leases:
Individually evaluated for impairment	4		5
Collectively evaluated for impairment	5,568		5,033
Allowance on loans and leases	5,572		5,038
Carrying value of loans and leases:
Individually evaluated for impairment	1,377		1,186
Collectively evaluated for impairment	631,540		588,118
Portfolio loans and leases	632,917		589,304
Commercial and industrial | Acquired
Carrying value of loans and leases:
Individually evaluated for impairment	487		711
Collectively evaluated for impairment	96,541		124,747
Portfolio loans and leases	112,389		130,008
Commercial and industrial | Financial Asset Acquired With and Without Credit Deterioration
Allowance on loans and leases:
Individually evaluated for impairment	100		0
Collectively evaluated for impairment	0		0
Allowance on loans and leases	100		0
Consumer
Allowance on loans and leases:
Individually evaluated for impairment	4		4
Collectively evaluated for impairment	285		242
Allowance on loans and leases	289	291	246	177	135	153
Carrying value of loans and leases:
Individually evaluated for impairment	27		27
Collectively evaluated for impairment	51,435		38,126
Portfolio loans and leases	51,462		38,153
Consumer | Purchased credit-impaired
Allowance on loans and leases:
Allowance on loans and leases	0		0
Carrying value of loans and leases:
Portfolio loans and leases	0		0
Consumer | Originated
Allowance on loans and leases:
Individually evaluated for impairment	4		4
Collectively evaluated for impairment	285		242
Allowance on loans and leases	289		246
Carrying value of loans and leases:
Individually evaluated for impairment	27		27
Collectively evaluated for impairment	49,801		35,119
Portfolio loans and leases	49,828		35,146
Consumer | Acquired
Carrying value of loans and leases:
Individually evaluated for impairment	0		0
Collectively evaluated for impairment	1,634		3,007
Portfolio loans and leases	1,634		3,007
Consumer | Financial Asset Acquired With and Without Credit Deterioration
Allowance on loans and leases:
Individually evaluated for impairment	0		0
Collectively evaluated for impairment	0		0
Allowance on loans and leases	0		0
Leases
Allowance on loans and leases:
Individually evaluated for impairment	0		0
Collectively evaluated for impairment	1,380		742
Allowance on loans and leases	1,380	1,049	742	700	579	559
Carrying value of loans and leases:
Individually evaluated for impairment	0		0
Collectively evaluated for impairment	132,649		115,401
Portfolio loans and leases	132,649		115,401
Leases | Purchased credit-impaired
Allowance on loans and leases:
Allowance on loans and leases	0		0
Carrying value of loans and leases:
Portfolio loans and leases	0		0
Leases | Originated
Allowance on loans and leases:
Individually evaluated for impairment	0		0
Collectively evaluated for impairment	1,380		742
Allowance on loans and leases	1,380		742
Carrying value of loans and leases:
Individually evaluated for impairment	0		0
Collectively evaluated for impairment	97,506		68,035
Portfolio loans and leases	97,506		68,035
Leases | Acquired
Carrying value of loans and leases:
Individually evaluated for impairment	0		0
Collectively evaluated for impairment	35,143		47,366
Portfolio loans and leases	35,143		47,366
Leases | Financial Asset Acquired With and Without Credit Deterioration
Allowance on loans and leases:
Individually evaluated for impairment	0		0
Collectively evaluated for impairment	0		0
Allowance on loans and leases	0		0
Unallocated
Allowance on loans and leases:
Individually evaluated for impairment	0		0
Collectively evaluated for impairment	0		0
Allowance on loans and leases	0	$ 0	0	$ 0	$ 0	$ 0
Unallocated | Purchased credit-impaired
Allowance on loans and leases:
Allowance on loans and leases	$ 0		$ 0