Loans and reserve for credit losses (Past Due Financing Receivables) (Details) - USD ($) $ in Thousands	Sep. 30, 2016	Dec. 31, 2015
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	$ 5,929	$ 6,775
Current	2,055,579	1,681,154
Total loans	2,061,508	1,687,929
30-89 days past due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	4,627	5,266
90 days or more past due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	1,302	1,509
Commercial real estate | Owner occupied
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	708	1,739
Current	375,295	306,592
Total loans	376,003	308,331
Commercial real estate | Owner occupied | 30-89 days past due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	218	1,020
Commercial real estate | Owner occupied | 90 days or more past due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	490	719
Commercial real estate | Non-owner occupied
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	0	2,642
Current	588,777	523,920
Total loans	588,777	526,562
Commercial real estate | Non-owner occupied | 30-89 days past due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	0	2,642
Commercial real estate | Non-owner occupied | 90 days or more past due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	0	0
Commercial real estate | Commercial real estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	708	4,381
Current	964,072	830,512
Total loans	964,780	834,893
Commercial real estate | Commercial real estate | 30-89 days past due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	218	3,662
Commercial real estate | Commercial real estate | 90 days or more past due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	490	719
Construction | Construction
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	21	46
Current	182,960	130,306
Total loans	182,981	130,352
Construction | Construction | 30-89 days past due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	0	46
Construction | Construction | 90 days or more past due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	21	0
Residential real estate | Residential real estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	4,383	1,478
Current	461,083	296,912
Total loans	465,466	298,390
Residential real estate | Residential real estate | 30-89 days past due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	3,797	944
Residential real estate | Residential real estate | 90 days or more past due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	586	534
Commercial and industrial | Commercial and industrial
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	560	596
Current	404,709	383,848
Total loans	405,269	384,444
Commercial and industrial | Commercial and industrial | 30-89 days past due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	381	352
Commercial and industrial | Commercial and industrial | 90 days or more past due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	179	244
Consumer | Consumer
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	257	274
Current	42,755	39,576
Total loans	43,012	39,850
Consumer | Consumer | 30-89 days past due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	231	262
Consumer | Consumer | 90 days or more past due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	26	12
Originated Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	3,878	3,334
Current	1,758,846	1,449,644
Total loans	1,762,724	1,452,978
Originated Loans | 30-89 days past due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	3,191	2,364
Originated Loans | 90 days or more past due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	687	970
Originated Loans | Commercial real estate | Owner occupied
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	697	1,739
Current	280,204	261,356
Total loans	280,901	263,095
Originated Loans | Commercial real estate | Owner occupied | 30-89 days past due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	207	1,020
Originated Loans | Commercial real estate | Owner occupied | 90 days or more past due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	490	719
Originated Loans | Commercial real estate | Non-owner occupied
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	0	593
Current	486,689	430,786
Total loans	486,689	431,379
Originated Loans | Commercial real estate | Non-owner occupied | 30-89 days past due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	0	593
Originated Loans | Commercial real estate | Non-owner occupied | 90 days or more past due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	0	0
Originated Loans | Commercial real estate | Commercial real estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	697	2,332
Current	766,893	692,142
Total loans	767,590	694,474
Originated Loans | Commercial real estate | Commercial real estate | 30-89 days past due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	207	1,613
Originated Loans | Commercial real estate | Commercial real estate | 90 days or more past due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	490	719
Originated Loans | Construction | Construction
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	0	0
Current	168,558	119,723
Total loans	168,558	119,723
Originated Loans | Construction | Construction | 30-89 days past due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	0	0
Originated Loans | Construction | Construction | 90 days or more past due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	0	0
Originated Loans | Residential real estate | Residential real estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	2,625	196
Current	403,749	236,888
Total loans	406,374	237,084
Originated Loans | Residential real estate | Residential real estate | 30-89 days past due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	2,625	196
Originated Loans | Residential real estate | Residential real estate | 90 days or more past due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	0	0
Originated Loans | Commercial and industrial | Commercial and industrial
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	327	585
Current	378,373	362,750
Total loans	378,700	363,335
Originated Loans | Commercial and industrial | Commercial and industrial | 30-89 days past due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	156	346
Originated Loans | Commercial and industrial | Commercial and industrial | 90 days or more past due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	171	239
Originated Loans | Consumer | Consumer
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	229	221
Current	41,273	38,141
Total loans	41,502	38,362
Originated Loans | Consumer | Consumer | 30-89 days past due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	203	209
Originated Loans | Consumer | Consumer | 90 days or more past due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	26	12
Acquired Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	2,051	3,441
Current	296,733	231,510
Total loans	298,784	234,951
Acquired Loans | 30-89 days past due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	1,436	2,902
Acquired Loans | 90 days or more past due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	615	539
Acquired Loans | Commercial real estate | Owner occupied
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	11	0
Current	95,091	45,236
Total loans	95,102	45,236
Acquired Loans | Commercial real estate | Owner occupied | 30-89 days past due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	11	0
Acquired Loans | Commercial real estate | Owner occupied | 90 days or more past due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	0	0
Acquired Loans | Commercial real estate | Non-owner occupied
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	0	2,049
Current	102,088	93,134
Total loans	102,088	95,183
Acquired Loans | Commercial real estate | Non-owner occupied | 30-89 days past due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	0	2,049
Acquired Loans | Commercial real estate | Non-owner occupied | 90 days or more past due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	0	0
Acquired Loans | Commercial real estate | Commercial real estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	11	2,049
Current	197,179	138,370
Total loans	197,190	140,419
Acquired Loans | Commercial real estate | Commercial real estate | 30-89 days past due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	11	2,049
Acquired Loans | Commercial real estate | Commercial real estate | 90 days or more past due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	0	0
Acquired Loans | Construction | Construction
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	21	46
Current	14,402	10,583
Total loans	14,423	10,629
Acquired Loans | Construction | Construction | 30-89 days past due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	0	46
Acquired Loans | Construction | Construction | 90 days or more past due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	21	0
Acquired Loans | Residential real estate | Residential real estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	1,758	1,282
Current	57,334	60,024
Total loans	59,092	61,306
Acquired Loans | Residential real estate | Residential real estate | 30-89 days past due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	1,172	748
Acquired Loans | Residential real estate | Residential real estate | 90 days or more past due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	586	534
Acquired Loans | Commercial and industrial | Commercial and industrial
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	233	11
Current	26,336	21,098
Total loans	26,569	21,109
Acquired Loans | Commercial and industrial | Commercial and industrial | 30-89 days past due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	225	6
Acquired Loans | Commercial and industrial | Commercial and industrial | 90 days or more past due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	8	5
Acquired Loans | Consumer | Consumer
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	28	53
Current	1,482	1,435
Total loans	1,510	1,488
Acquired Loans | Consumer | Consumer | 30-89 days past due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	28	53
Acquired Loans | Consumer | Consumer | 90 days or more past due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	$ 0	$ 0