Loans and reserve for credit losses (Financing Receivable Credit Quality Indicators) (Details) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	$ 2,115,572	$ 2,104,412
Acceptable
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	2,027,314	2,018,583
Pass-Watch
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	33,881	31,954
Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	19,785	20,559
Substandard
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	34,592	33,316
Commercial real estate | Owner occupied
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	381,218	391,211
Commercial real estate | Non-owner occupied
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	623,888	612,397
Commercial real estate | Commercial real estate
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	1,005,106	1,003,608
Commercial real estate | Acceptable | Owner occupied
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	361,021	368,306
Commercial real estate | Acceptable | Non-owner occupied
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	599,047	588,440
Commercial real estate | Acceptable | Commercial real estate
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	960,068	956,746
Commercial real estate | Pass-Watch | Owner occupied
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	9,782	12,229
Commercial real estate | Pass-Watch | Non-owner occupied
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	7,634	6,201
Commercial real estate | Pass-Watch | Commercial real estate
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	17,416	18,430
Commercial real estate | Special Mention | Owner occupied
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	5,687	2,965
Commercial real estate | Special Mention | Non-owner occupied
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	10,849	12,142
Commercial real estate | Special Mention | Commercial real estate
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	16,536	15,107
Commercial real estate | Substandard | Owner occupied
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	4,728	7,711
Commercial real estate | Substandard | Non-owner occupied
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	6,358	5,614
Commercial real estate | Substandard | Commercial real estate
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	11,086	13,325
Construction | Construction
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	216,259	211,038
Construction | Acceptable | Construction
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	215,850	210,609
Construction | Pass-Watch | Construction
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	0	0
Construction | Special Mention | Construction
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	0	0
Construction | Substandard | Construction
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	409	429
Residential real estate | Residential real estate
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	436,907	431,842
Residential real estate | Acceptable | Residential real estate
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	434,717	428,202
Residential real estate | Pass-Watch | Residential real estate
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	814	1,988
Residential real estate | Special Mention | Residential real estate
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	0	0
Residential real estate | Substandard | Residential real estate
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	1,376	1,652
Commercial and industrial | Commercial and industrial
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	414,735	414,436
Commercial and industrial | Acceptable | Commercial and industrial
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	374,143	379,550
Commercial and industrial | Pass-Watch | Commercial and industrial
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	15,651	11,536
Commercial and industrial | Special Mention | Commercial and industrial
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	3,249	5,452
Commercial and industrial | Substandard | Commercial and industrial
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	21,692	17,898
Consumer | Consumer
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	42,565	43,488
Consumer | Acceptable | Consumer
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	42,536	43,476
Consumer | Pass-Watch | Consumer
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	0	0
Consumer | Special Mention | Consumer
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	0	0
Consumer | Substandard | Consumer
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	29	12
Originated Loans
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	1,855,290	1,819,334
Originated Loans | Acceptable
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	1,792,460	1,760,349
Originated Loans | Pass-Watch
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	25,462	22,713
Originated Loans | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	11,432	10,934
Originated Loans | Substandard
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	25,936	25,338
Originated Loans | Commercial real estate | Owner occupied
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	297,105	298,721
Originated Loans | Commercial real estate | Non-owner occupied
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	529,025	514,363
Originated Loans | Commercial real estate | Commercial real estate
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	826,130	813,084
Originated Loans | Commercial real estate | Acceptable | Owner occupied
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	283,767	282,438
Originated Loans | Commercial real estate | Acceptable | Non-owner occupied
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	520,588	506,946
Originated Loans | Commercial real estate | Acceptable | Commercial real estate
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	804,355	789,384
Originated Loans | Commercial real estate | Pass-Watch | Owner occupied
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	6,560	9,007
Originated Loans | Commercial real estate | Pass-Watch | Non-owner occupied
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	3,307	2,234
Originated Loans | Commercial real estate | Pass-Watch | Commercial real estate
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	9,867	11,241
Originated Loans | Commercial real estate | Special Mention | Owner occupied
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	4,046	1,302
Originated Loans | Commercial real estate | Special Mention | Non-owner occupied
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	4,137	4,180
Originated Loans | Commercial real estate | Special Mention | Commercial real estate
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	8,183	5,482
Originated Loans | Commercial real estate | Substandard | Owner occupied
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	2,732	5,974
Originated Loans | Commercial real estate | Substandard | Non-owner occupied
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	993	1,003
Originated Loans | Commercial real estate | Substandard | Commercial real estate
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	3,725	6,977
Originated Loans | Construction | Construction
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	212,812	200,654
Originated Loans | Construction | Acceptable | Construction
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	212,436	200,278
Originated Loans | Construction | Pass-Watch | Construction
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	0	0
Originated Loans | Construction | Special Mention | Construction
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	0	0
Originated Loans | Construction | Substandard | Construction
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	376	376
Originated Loans | Residential real estate | Residential real estate
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	387,507	377,374
Originated Loans | Residential real estate | Acceptable | Residential real estate
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	386,808	376,713
Originated Loans | Residential real estate | Pass-Watch | Residential real estate
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	0	0
Originated Loans | Residential real estate | Special Mention | Residential real estate
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	0	0
Originated Loans | Residential real estate | Substandard | Residential real estate
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	699	661
Originated Loans | Commercial and industrial | Commercial and industrial
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	387,548	386,150
Originated Loans | Commercial and industrial | Acceptable | Commercial and industrial
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	347,597	351,914
Originated Loans | Commercial and industrial | Pass-Watch | Commercial and industrial
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	15,595	11,472
Originated Loans | Commercial and industrial | Special Mention | Commercial and industrial
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	3,249	5,452
Originated Loans | Commercial and industrial | Substandard | Commercial and industrial
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	21,107	17,312
Originated Loans | Consumer | Consumer
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	41,293	42,072
Originated Loans | Consumer | Acceptable | Consumer
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	41,264	42,060
Originated Loans | Consumer | Pass-Watch | Consumer
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	0	0
Originated Loans | Consumer | Special Mention | Consumer
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	0	0
Originated Loans | Consumer | Substandard | Consumer
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	29	12
Acquired Loans
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	260,282	285,078
Acquired Loans | Acceptable
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	234,854	258,234
Acquired Loans | Pass-Watch
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	8,419	9,241
Acquired Loans | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	8,353	9,625
Acquired Loans | Substandard
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	8,656	7,978
Acquired Loans | Commercial real estate | Owner occupied
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	84,113	92,490
Acquired Loans | Commercial real estate | Non-owner occupied
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	94,863	98,034
Acquired Loans | Commercial real estate | Commercial real estate
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	178,976	190,524
Acquired Loans | Commercial real estate | Acceptable | Owner occupied
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	77,254	85,868
Acquired Loans | Commercial real estate | Acceptable | Non-owner occupied
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	78,459	81,494
Acquired Loans | Commercial real estate | Acceptable | Commercial real estate
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	155,713	167,362
Acquired Loans | Commercial real estate | Pass-Watch | Owner occupied
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	3,222	3,222
Acquired Loans | Commercial real estate | Pass-Watch | Non-owner occupied
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	4,327	3,967
Acquired Loans | Commercial real estate | Pass-Watch | Commercial real estate
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	7,549	7,189
Acquired Loans | Commercial real estate | Special Mention | Owner occupied
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	1,641	1,663
Acquired Loans | Commercial real estate | Special Mention | Non-owner occupied
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	6,712	7,962
Acquired Loans | Commercial real estate | Special Mention | Commercial real estate
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	8,353	9,625
Acquired Loans | Commercial real estate | Substandard | Owner occupied
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	1,996	1,737
Acquired Loans | Commercial real estate | Substandard | Non-owner occupied
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	5,365	4,611
Acquired Loans | Commercial real estate | Substandard | Commercial real estate
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	7,361	6,348
Acquired Loans | Construction | Construction
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	3,447	10,384
Acquired Loans | Construction | Acceptable | Construction
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	3,414	10,331
Acquired Loans | Construction | Pass-Watch | Construction
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	0	0
Acquired Loans | Construction | Special Mention | Construction
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	0	0
Acquired Loans | Construction | Substandard | Construction
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	33	53
Acquired Loans | Residential real estate | Residential real estate
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	49,400	54,468
Acquired Loans | Residential real estate | Acceptable | Residential real estate
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	47,909	51,489
Acquired Loans | Residential real estate | Pass-Watch | Residential real estate
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	814	1,988
Acquired Loans | Residential real estate | Special Mention | Residential real estate
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	0	0
Acquired Loans | Residential real estate | Substandard | Residential real estate
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	677	991
Acquired Loans | Commercial and industrial | Commercial and industrial
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	27,187	28,286
Acquired Loans | Commercial and industrial | Acceptable | Commercial and industrial
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	26,546	27,636
Acquired Loans | Commercial and industrial | Pass-Watch | Commercial and industrial
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	56	64
Acquired Loans | Commercial and industrial | Special Mention | Commercial and industrial
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	0	0
Acquired Loans | Commercial and industrial | Substandard | Commercial and industrial
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	585	586
Acquired Loans | Consumer | Consumer
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	1,272	1,416
Acquired Loans | Consumer | Acceptable | Consumer
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	1,272	1,416
Acquired Loans | Consumer | Pass-Watch | Consumer
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	0	0
Acquired Loans | Consumer | Special Mention | Consumer
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	0	0
Acquired Loans | Consumer | Substandard | Consumer
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	$ 0	$ 0