Loans and reserve for credit losses (Financing Receivable Credit Quality Indicators) (Details) - USD ($) $ in Thousands	Jun. 30, 2016	Dec. 31, 2015
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	$ 1,902,711	$ 1,687,929
Acceptable
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	1,812,297	1,571,542
Pass-Watch
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	28,385	36,052
Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	20,824	40,836
Substandard
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	41,205	39,499
Commercial real estate | Owner occupied
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	320,775	308,331
Commercial real estate | Non-owner occupied
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	547,307	526,562
Commercial real estate | Commercial real estate
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	868,082	834,893
Commercial real estate | Acceptable | Owner occupied
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	300,961	277,194
Commercial real estate | Acceptable | Non-owner occupied
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	520,921	482,471
Commercial real estate | Acceptable | Commercial real estate
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	821,882	759,665
Commercial real estate | Pass-Watch | Owner occupied
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	10,329	12,103
Commercial real estate | Pass-Watch | Non-owner occupied
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	4,626	12,576
Commercial real estate | Pass-Watch | Commercial real estate
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	14,955	24,679
Commercial real estate | Special Mention | Owner occupied
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	2,188	8,767
Commercial real estate | Special Mention | Non-owner occupied
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	13,214	13,908
Commercial real estate | Special Mention | Commercial real estate
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	15,402	22,675
Commercial real estate | Substandard | Owner occupied
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	7,297	10,267
Commercial real estate | Substandard | Non-owner occupied
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	8,546	17,607
Commercial real estate | Substandard | Commercial real estate
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	15,843	27,874
Construction | Construction
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	161,881	130,352
Construction | Acceptable | Construction
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	161,813	129,349
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	971
Construction | Substandard | Construction
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	68	32
Residential real estate | Residential real estate
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	421,334	298,390
Residential real estate | Acceptable | Residential real estate
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	419,990	296,725
Residential real estate | Pass-Watch | Residential real estate
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	0	0
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	1,344	1,665
Commercial and industrial | Commercial and industrial
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	410,032	384,444
Commercial and industrial | Acceptable | Commercial and industrial
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	367,232	345,968
Commercial and industrial | Pass-Watch | Commercial and industrial
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	13,430	11,373
Commercial and industrial | Special Mention | Commercial and industrial
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	5,422	17,190
Commercial and industrial | Substandard | Commercial and industrial
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	23,948	9,913
Consumer | Consumer
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	41,382	39,850
Consumer | Acceptable | Consumer
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	41,380	39,835
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	2	15
Originated Loans
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	1,693,850	1,452,978
Originated Loans | Acceptable
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	1,624,430	1,376,860
Originated Loans | Pass-Watch
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	23,967	29,668
Originated Loans | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	11,260	20,648
Originated Loans | Substandard
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	34,193	25,802
Originated Loans | Commercial real estate | Owner occupied
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	280,421	263,095
Originated Loans | Commercial real estate | Non-owner occupied
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	462,163	431,379
Originated Loans | Commercial real estate | Commercial real estate
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	742,584	694,474
Originated Loans | Commercial real estate | Acceptable | Owner occupied
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	266,099	243,113
Originated Loans | Commercial real estate | Acceptable | Non-owner occupied
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	449,614	411,137
Originated Loans | Commercial real estate | Acceptable | Commercial real estate
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	715,713	654,250
Originated Loans | Commercial real estate | Pass-Watch | Owner occupied
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	6,884	8,623
Originated Loans | Commercial real estate | Pass-Watch | Non-owner occupied
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	3,745	9,825
Originated Loans | Commercial real estate | Pass-Watch | Commercial real estate
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	10,629	18,448
Originated Loans | Commercial real estate | Special Mention | Owner occupied
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	975	1,426
Originated Loans | Commercial real estate | Special Mention | Non-owner occupied
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	4,863	4,522
Originated Loans | Commercial real estate | Special Mention | Commercial real estate
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	5,838	5,948
Originated Loans | Commercial real estate | Substandard | Owner occupied
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	6,463	9,933
Originated Loans | Commercial real estate | Substandard | Non-owner occupied
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	3,941	5,895
Originated Loans | Commercial real estate | Substandard | Commercial real estate
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	10,404	15,828
Originated Loans | Construction | Construction
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	151,914	119,723
Originated Loans | Construction | Acceptable | Construction
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	151,914	118,752
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	971
Originated Loans | Construction | Substandard | Construction
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	0	0
Originated Loans | Residential real estate | Residential real estate
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	369,802	237,084
Originated Loans | Residential real estate | Acceptable | Residential real estate
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	369,300	236,574
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	502	510
Originated Loans | Commercial and industrial | Commercial and industrial
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	389,319	363,335
Originated Loans | Commercial and industrial | Acceptable | Commercial and industrial
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	347,274	328,934
Originated Loans | Commercial and industrial | Pass-Watch | Commercial and industrial
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	13,338	11,220
Originated Loans | Commercial and industrial | Special Mention | Commercial and industrial
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	5,422	13,729
Originated Loans | Commercial and industrial | Substandard | Commercial and industrial
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	23,285	9,452
Originated Loans | Consumer | Consumer
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	40,231	38,362
Originated Loans | Consumer | Acceptable | Consumer
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	40,229	38,350
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	2	12
Acquired Loans
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	208,861	234,951
Acquired Loans | Acceptable
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	187,867	194,682
Acquired Loans | Pass-Watch
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	4,418	6,384
Acquired Loans | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	9,564	20,188
Acquired Loans | Substandard
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	7,000	13,697
Acquired Loans | Commercial real estate | Owner occupied
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	40,354	45,236
Acquired Loans | Commercial real estate | Non-owner occupied
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	85,144	95,183
Acquired Loans | Commercial real estate | Commercial real estate
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	125,498	140,419
Acquired Loans | Commercial real estate | Acceptable | Owner occupied
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	34,862	34,081
Acquired Loans | Commercial real estate | Acceptable | Non-owner occupied
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	71,307	71,334
Acquired Loans | Commercial real estate | Acceptable | Commercial real estate
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	106,169	105,415
Acquired Loans | Commercial real estate | Pass-Watch | Owner occupied
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	3,445	3,480
Acquired Loans | Commercial real estate | Pass-Watch | Non-owner occupied
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	881	2,751
Acquired Loans | Commercial real estate | Pass-Watch | Commercial real estate
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	4,326	6,231
Acquired Loans | Commercial real estate | Special Mention | Owner occupied
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	1,213	7,341
Acquired Loans | Commercial real estate | Special Mention | Non-owner occupied
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	8,351	9,386
Acquired Loans | Commercial real estate | Special Mention | Commercial real estate
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	9,564	16,727
Acquired Loans | Commercial real estate | Substandard | Owner occupied
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	834	334
Acquired Loans | Commercial real estate | Substandard | Non-owner occupied
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	4,605	11,712
Acquired Loans | Commercial real estate | Substandard | Commercial real estate
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	5,439	12,046
Acquired Loans | Construction | Construction
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	9,967	10,629
Acquired Loans | Construction | Acceptable | Construction
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	9,899	10,597
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	68	32
Acquired Loans | Residential real estate | Residential real estate
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	51,532	61,306
Acquired Loans | Residential real estate | Acceptable | Residential real estate
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	50,690	60,151
Acquired 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
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	842	1,155
Acquired Loans | Commercial and industrial | Commercial and industrial
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	20,713	21,109
Acquired Loans | Commercial and industrial | Acceptable | Commercial and industrial
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	19,958	17,034
Acquired Loans | Commercial and industrial | Pass-Watch | Commercial and industrial
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	92	153
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	3,461
Acquired Loans | Commercial and industrial | Substandard | Commercial and industrial
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	663	461
Acquired Loans | Consumer | Consumer
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	1,151	1,488
Acquired Loans | Consumer | Acceptable | Consumer
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	1,151	1,485
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	$ 3