Loans and reserve for credit losses (Financing Receivable Credit Quality Indicators) (Details) - USD ($) $ in Thousands	Sep. 30, 2016	Dec. 31, 2015
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	$ 2,061,508	$ 1,687,929
Acceptable
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	1,971,297	1,571,542
Pass-Watch
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	27,073	36,052
Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	21,930	40,836
Substandard
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	41,208	39,499
Commercial real estate | Owner occupied
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	376,003	308,331
Commercial real estate | Non-owner occupied
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	588,777	526,562
Commercial real estate | Commercial real estate
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	964,780	834,893
Commercial real estate | Acceptable | Owner occupied
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	356,094	277,194
Commercial real estate | Acceptable | Non-owner occupied
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	562,080	482,471
Commercial real estate | Acceptable | Commercial real estate
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	918,174	759,665
Commercial real estate | Pass-Watch | Owner occupied
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	9,252	12,103
Commercial real estate | Pass-Watch | Non-owner occupied
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	5,440	12,576
Commercial real estate | Pass-Watch | Commercial real estate
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	14,692	24,679
Commercial real estate | Special Mention | Owner occupied
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	2,654	8,767
Commercial real estate | Special Mention | Non-owner occupied
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	13,515	13,908
Commercial real estate | Special Mention | Commercial real estate
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	16,169	22,675
Commercial real estate | Substandard | Owner occupied
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	8,003	10,267
Commercial real estate | Substandard | Non-owner occupied
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	7,742	17,607
Commercial real estate | Substandard | Commercial real estate
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	15,745	27,874
Construction | Construction
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	182,981	130,352
Construction | Acceptable | Construction
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	182,921	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	60	32
Residential real estate | Residential real estate
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	465,466	298,390
Residential real estate | Acceptable | Residential real estate
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	462,384	296,725
Residential real estate | Pass-Watch | Residential real estate
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	1,550	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	1,532	1,665
Commercial and industrial | Commercial and industrial
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	405,269	384,444
Commercial and industrial | Acceptable | Commercial and industrial
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	364,832	345,968
Commercial and industrial | Pass-Watch | Commercial and industrial
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	10,831	11,373
Commercial and industrial | Special Mention | Commercial and industrial
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	5,761	17,190
Commercial and industrial | Substandard | Commercial and industrial
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	23,845	9,913
Consumer | Consumer
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	43,012	39,850
Consumer | Acceptable | Consumer
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	42,986	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	26	15
Originated Loans
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	1,762,724	1,452,978
Originated Loans | Acceptable
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	1,701,856	1,376,860
Originated Loans | Pass-Watch
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	18,674	29,668
Originated Loans | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	10,784	20,648
Originated Loans | Substandard
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	31,410	25,802
Originated Loans | Commercial real estate | Owner occupied
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	280,901	263,095
Originated Loans | Commercial real estate | Non-owner occupied
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	486,689	431,379
Originated Loans | Commercial real estate | Commercial real estate
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	767,590	694,474
Originated Loans | Commercial real estate | Acceptable | Owner occupied
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	266,610	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	479,207	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	745,817	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	6,811	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	1,589	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	8,400	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	1,091	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	4,520	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	5,611	5,948
Originated Loans | Commercial real estate | Substandard | Owner occupied
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	6,389	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	1,373	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	7,762	15,828
Originated Loans | Construction | Construction
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	168,558	119,723
Originated Loans | Construction | Acceptable | Construction
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	168,558	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	406,374	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	405,923	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	451	510
Originated Loans | Commercial and industrial | Commercial and industrial
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	378,700	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	340,082	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	10,274	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	5,173	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	23,171	9,452
Originated Loans | Consumer | Consumer
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	41,502	38,362
Originated Loans | Consumer | Acceptable | Consumer
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	41,476	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	26	12
Acquired Loans
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	298,784	234,951
Acquired Loans | Acceptable
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	269,441	194,682
Acquired Loans | Pass-Watch
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	8,399	6,384
Acquired Loans | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	11,146	20,188
Acquired Loans | Substandard
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	9,798	13,697
Acquired Loans | Commercial real estate | Owner occupied
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	95,102	45,236
Acquired Loans | Commercial real estate | Non-owner occupied
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	102,088	95,183
Acquired Loans | Commercial real estate | Commercial real estate
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	197,190	140,419
Acquired Loans | Commercial real estate | Acceptable | Owner occupied
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	89,484	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	82,873	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	172,357	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	2,441	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	3,851	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	6,292	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	1,563	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	8,995	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	10,558	16,727
Acquired Loans | Commercial real estate | Substandard | Owner occupied
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	1,614	334
Acquired Loans | Commercial real estate | Substandard | Non-owner occupied
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	6,369	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	7,983	12,046
Acquired Loans | Construction | Construction
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	14,423	10,629
Acquired Loans | Construction | Acceptable | Construction
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	14,363	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	60	32
Acquired Loans | Residential real estate | Residential real estate
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	59,092	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	56,461	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	1,550	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	1,081	1,155
Acquired Loans | Commercial and industrial | Commercial and industrial
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	26,569	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	24,750	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	557	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	588	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	674	461
Acquired Loans | Consumer | Consumer
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	1,510	1,488
Acquired Loans | Consumer | Acceptable | Consumer
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable, before fees, gross, amount	1,510	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