Loans and Leases - Past Due Loans and Leases (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans and leases, past due	$ 9,119	$ 7,959
Loans and leases, current	3,363,366	3,269,320
Loans and leases, accruing	3,372,485	3,277,279
Non-accrual loans and leases	8,990	8,579
Total portfolio loans and leases	3,381,475	3,285,858
Originated
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans and leases, past due	5,186	3,081
Loans and leases, current	2,741,577	2,480,470
Loans and leases, accruing	2,746,763	2,483,551
Non-accrual loans and leases	5,397	3,745
Total portfolio loans and leases	2,752,160	2,487,296
Acquired
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans and leases, past due	3,933	4,878
Loans and leases, current	621,789	788,850
Loans and leases, accruing	625,722	793,728
Non-accrual loans and leases	3,593	4,834
Total portfolio loans and leases	629,315	798,562
Administratively Delinquent
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans and leases, current	720	4,100
Commercial mortgage
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans and leases, past due	2,468	3,794
Loans and leases, current	1,615,290	1,518,711
Loans and leases, accruing	1,617,758	1,522,505
Non-accrual loans and leases	735	872
Total portfolio loans and leases	1,618,493	1,523,377
Commercial mortgage | Originated
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans and leases, past due	76	1,336
Loans and leases, current	1,259,321	1,120,901
Loans and leases, accruing	1,259,397	1,122,237
Non-accrual loans and leases	0	90
Total portfolio loans and leases	1,259,397	1,122,327
Commercial mortgage | Acquired
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans and leases, past due	2,392	2,458
Loans and leases, current	355,969	397,810
Loans and leases, accruing	358,361	400,268
Non-accrual loans and leases	735	782
Total portfolio loans and leases	359,096	401,050
Home equity loans and lines
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans and leases, past due	324	348
Loans and leases, current	205,549	216,446
Loans and leases, accruing	205,873	216,794
Non-accrual loans and leases	1,933	1,481
Total portfolio loans and leases	207,806	218,275
Home equity loans and lines | Originated
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans and leases, past due	250	26
Loans and leases, current	178,126	182,036
Loans and leases, accruing	178,376	182,062
Non-accrual loans and leases	1,692	1,221
Total portfolio loans and leases	180,068	183,283
Home equity loans and lines | Acquired
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans and leases, past due	74	322
Loans and leases, current	27,423	34,410
Loans and leases, accruing	27,497	34,732
Non-accrual loans and leases	241	260
Total portfolio loans and leases	27,738	34,992
Residential mortgage
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans and leases, past due	2,397	1,465
Loans and leases, current	462,235	453,004
Loans and leases, accruing	464,632	454,469
Non-accrual loans and leases	2,770	4,417
Total portfolio loans and leases	467,402	458,886
Residential mortgage | Originated
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans and leases, past due	1,475	721
Loans and leases, current	377,594	358,709
Loans and leases, accruing	379,069	359,430
Non-accrual loans and leases	1,968	1,505
Total portfolio loans and leases	381,037	360,935
Residential mortgage | Acquired
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans and leases, past due	922	744
Loans and leases, current	84,641	94,295
Loans and leases, accruing	85,563	95,039
Non-accrual loans and leases	802	2,912
Total portfolio loans and leases	86,365	97,951
Construction
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans and leases, past due	488	0
Loans and leases, current	177,714	212,454
Loans and leases, accruing	178,202	212,454
Non-accrual loans and leases	291	0
Total portfolio loans and leases	178,493	212,454
Construction | Originated
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans and leases, past due	488	0
Loans and leases, current	157,912	128,266
Loans and leases, accruing	158,400	128,266
Non-accrual loans and leases	291	0
Total portfolio loans and leases	158,691	128,266
Construction | Acquired
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans and leases, past due	0	0
Loans and leases, current	19,802	84,188
Loans and leases, accruing	19,802	84,188
Non-accrual loans and leases	0	0
Total portfolio loans and leases	19,802	84,188
Commercial and industrial
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans and leases, past due	2,370	944
Loans and leases, current	718,847	716,662
Loans and leases, accruing	721,217	717,606
Non-accrual loans and leases	1,782	1,706
Total portfolio loans and leases	722,999	719,312
Commercial and industrial | Originated
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans and leases, past due	2,306	675
Loans and leases, current	614,969	587,803
Loans and leases, accruing	617,275	588,478
Non-accrual loans and leases	925	826
Total portfolio loans and leases	618,200	589,304
Commercial and industrial | Acquired
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans and leases, past due	64	269
Loans and leases, current	103,878	128,859
Loans and leases, accruing	103,942	129,128
Non-accrual loans and leases	857	880
Total portfolio loans and leases	104,799	130,008
Consumer
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans and leases, past due	69	1,106
Loans and leases, current	47,623	37,047
Loans and leases, accruing	47,692	38,153
Non-accrual loans and leases	117	0
Total portfolio loans and leases	47,809	38,153
Consumer | Originated
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans and leases, past due	69	21
Loans and leases, current	44,722	35,125
Loans and leases, accruing	44,791	35,146
Non-accrual loans and leases	42	0
Total portfolio loans and leases	44,833	35,146
Consumer | Acquired
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans and leases, past due	0	1,085
Loans and leases, current	2,901	1,922
Loans and leases, accruing	2,901	3,007
Non-accrual loans and leases	75	0
Total portfolio loans and leases	2,976	3,007
Leases
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans and leases, past due	1,003	302
Loans and leases, current	136,108	114,996
Loans and leases, accruing	137,111	115,298
Non-accrual loans and leases	1,362	103
Total portfolio loans and leases	138,473	115,401
Leases | Originated
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans and leases, past due	522	302
Loans and leases, current	108,933	67,630
Loans and leases, accruing	109,455	67,932
Non-accrual loans and leases	479	103
Total portfolio loans and leases	109,934	68,035
Leases | Acquired
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans and leases, past due	481	0
Loans and leases, current	27,175	47,366
Loans and leases, accruing	27,656	47,366
Non-accrual loans and leases	883	0
Total portfolio loans and leases	28,539	47,366
30 – 59 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans and leases, past due	4,942	4,979
30 – 59 Days Past Due | Originated
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans and leases, past due	3,717	2,587
30 – 59 Days Past Due | Acquired
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans and leases, past due	1,225	2,392
30 – 59 Days Past Due | Commercial mortgage
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans and leases, past due	0	1,366
30 – 59 Days Past Due | Commercial mortgage | Originated
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans and leases, past due	0	1,255
30 – 59 Days Past Due | Commercial mortgage | Acquired
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans and leases, past due	0	111
30 – 59 Days Past Due | Home equity loans and lines
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans and leases, past due	324	338
30 – 59 Days Past Due | Home equity loans and lines | Originated
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans and leases, past due	250	26
30 – 59 Days Past Due | Home equity loans and lines | Acquired
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans and leases, past due	74	312
30 – 59 Days Past Due | Residential mortgage
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans and leases, past due	2,218	1,386
30 – 59 Days Past Due | Residential mortgage | Originated
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans and leases, past due	1,475	721
30 – 59 Days Past Due | Residential mortgage | Acquired
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans and leases, past due	743	665
30 – 59 Days Past Due | Construction
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans and leases, past due	488	0
30 – 59 Days Past Due | Construction | Originated
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans and leases, past due	488	0
30 – 59 Days Past Due | Construction | Acquired
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans and leases, past due	0	0
30 – 59 Days Past Due | Commercial and industrial
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans and leases, past due	1,115	658
30 – 59 Days Past Due | Commercial and industrial | Originated
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans and leases, past due	1,051	439
30 – 59 Days Past Due | Commercial and industrial | Acquired
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans and leases, past due	64	219
30 – 59 Days Past Due | Consumer
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans and leases, past due	46	1,106
30 – 59 Days Past Due | Consumer | Originated
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans and leases, past due	46	21
30 – 59 Days Past Due | Consumer | Acquired
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans and leases, past due	0	1,085
30 – 59 Days Past Due | Leases
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans and leases, past due	751	125
30 – 59 Days Past Due | Leases | Originated
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans and leases, past due	407	125
30 – 59 Days Past Due | Leases | Acquired
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans and leases, past due	344	0
60 – 89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans and leases, past due	4,177	2,980
60 – 89 Days Past Due | Originated
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans and leases, past due	1,469	494
60 – 89 Days Past Due | Acquired
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans and leases, past due	2,708	2,486
60 – 89 Days Past Due | Commercial mortgage
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans and leases, past due	2,468	2,428
60 – 89 Days Past Due | Commercial mortgage | Originated
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans and leases, past due	76	81
60 – 89 Days Past Due | Commercial mortgage | Acquired
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans and leases, past due	2,392	2,347
60 – 89 Days Past Due | Home equity loans and lines
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans and leases, past due	0	10
60 – 89 Days Past Due | Home equity loans and lines | Originated
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans and leases, past due	0	0
60 – 89 Days Past Due | Home equity loans and lines | Acquired
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans and leases, past due	0	10
60 – 89 Days Past Due | Residential mortgage
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans and leases, past due	179	79
60 – 89 Days Past Due | Residential mortgage | Originated
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans and leases, past due	0	0
60 – 89 Days Past Due | Residential mortgage | Acquired
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans and leases, past due	179	79
60 – 89 Days Past Due | Construction
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans and leases, past due	0	0
60 – 89 Days Past Due | Construction | Originated
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans and leases, past due	0	0
60 – 89 Days Past Due | Construction | Acquired
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans and leases, past due	0	0
60 – 89 Days Past Due | Commercial and industrial
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans and leases, past due	1,255	286
60 – 89 Days Past Due | Commercial and industrial | Originated
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans and leases, past due	1,255	236
60 – 89 Days Past Due | Commercial and industrial | Acquired
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans and leases, past due	0	50
60 – 89 Days Past Due | Consumer
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans and leases, past due	23	0
60 – 89 Days Past Due | Consumer | Originated
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans and leases, past due	23	0
60 – 89 Days Past Due | Consumer | Acquired
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans and leases, past due	0	0
60 – 89 Days Past Due | Leases
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans and leases, past due	252	177
60 – 89 Days Past Due | Leases | Originated
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans and leases, past due	115	177
60 – 89 Days Past Due | Leases | Acquired
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans and leases, past due	137	0
Over 89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans and leases, past due	0	0
Over 89 Days Past Due | Originated
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans and leases, past due	0	0
Over 89 Days Past Due | Acquired
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans and leases, past due	0	0
Over 89 Days Past Due | Commercial mortgage
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans and leases, past due	0	0
Over 89 Days Past Due | Commercial mortgage | Originated
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans and leases, past due	0	0
Over 89 Days Past Due | Commercial mortgage | Acquired
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans and leases, past due	0	0
Over 89 Days Past Due | Home equity loans and lines
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans and leases, past due	0	0
Over 89 Days Past Due | Home equity loans and lines | Originated
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans and leases, past due	0	0
Over 89 Days Past Due | Home equity loans and lines | Acquired
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans and leases, past due	0	0
Over 89 Days Past Due | Residential mortgage
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans and leases, past due	0	0
Over 89 Days Past Due | Residential mortgage | Originated
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans and leases, past due	0	0
Over 89 Days Past Due | Residential mortgage | Acquired
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans and leases, past due	0	0
Over 89 Days Past Due | Construction
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans and leases, past due	0	0
Over 89 Days Past Due | Construction | Originated
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans and leases, past due	0	0
Over 89 Days Past Due | Construction | Acquired
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans and leases, past due	0	0
Over 89 Days Past Due | Commercial and industrial
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans and leases, past due	0	0
Over 89 Days Past Due | Commercial and industrial | Originated
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans and leases, past due	0	0
Over 89 Days Past Due | Commercial and industrial | Acquired
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans and leases, past due	0	0
Over 89 Days Past Due | Consumer
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans and leases, past due	0	0
Over 89 Days Past Due | Consumer | Originated
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans and leases, past due	0	0
Over 89 Days Past Due | Consumer | Acquired
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans and leases, past due	0	0
Over 89 Days Past Due | Leases
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans and leases, past due	0	0
Over 89 Days Past Due | Leases | Originated
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans and leases, past due	0	0
Over 89 Days Past Due | Leases | Acquired
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans and leases, past due	0	0
Originated Loans | Administratively Delinquent
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans and leases, current	720	4,000
Acquired Loans | Administratively Delinquent
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans and leases, current	$ 0	$ 102