Loans and allowance for loan losses (Details 4) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Impaired Loans With No Related Allowance Recorded [Abstract]
Average Recorded Investment	$ 18,532	$ 30,892	$ 19,786	$ 28,561
Interest Income Recognized	212	338	473	717
Impaired Loans With Related Allowance Recorded [Abstract]
Average Recorded Investment	9,310	8,419	9,315	8,187
Interest Income Recognized	79	12	155	112
Total [Abstract]
Average Recorded Investment	27,842	39,311	29,101	36,748
Interest Income Recognized	291	350	628	829
Construction and Land Development [Member]
Impaired Loans With No Related Allowance Recorded [Abstract]
Average Recorded Investment	2,617	4,133	2,906	4,344
Interest Income Recognized	27	42	67	100
Total [Abstract]
Average Recorded Investment	3,242	4,735	3,512	4,950
Interest Income Recognized	34	49	78	115
Residential [Member]
Impaired Loans With No Related Allowance Recorded [Abstract]
Average Recorded Investment	0	182	115	384
Interest Income Recognized	0	0	1	2
Total [Abstract]
Average Recorded Investment	0	182	115	384
Interest Income Recognized	0	0	1	2
Commercial [Member]
Impaired Loans With No Related Allowance Recorded [Abstract]
Average Recorded Investment	2,617	3,951	2,791	3,960
Interest Income Recognized	27	42	66	98
Impaired Loans With Related Allowance Recorded [Abstract]
Average Recorded Investment	625	602	606	606
Interest Income Recognized	7	7	11	15
Total [Abstract]
Average Recorded Investment	3,242	4,553	3,397	4,566
Interest Income Recognized	34	49	77	113
Commercial Real Estate [Member]
Impaired Loans With No Related Allowance Recorded [Abstract]
Average Recorded Investment	7,585	15,300	8,400	13,674
Interest Income Recognized	84	156	194	351
Impaired Loans With Related Allowance Recorded [Abstract]
Average Recorded Investment	6,754	5,747	6,727	5,406
Interest Income Recognized	61	0	128	92
Total [Abstract]
Average Recorded Investment	14,339	21,047	15,127	19,080
Interest Income Recognized	145	156	322	443
Owner Occupied [Member]
Impaired Loans With No Related Allowance Recorded [Abstract]
Average Recorded Investment	1,201	2,970	1,439	2,345
Interest Income Recognized	14	38	31	65
Impaired Loans With Related Allowance Recorded [Abstract]
Average Recorded Investment	6,534	4,459	6,565	1,298
Interest Income Recognized	50	0	116	92
Total [Abstract]
Average Recorded Investment	7,735	7,429	8,005	3,643
Interest Income Recognized	64	38	147	157
Non-Owner Occupied [Member]
Impaired Loans With No Related Allowance Recorded [Abstract]
Average Recorded Investment	6,384	9,957	6,473	8,949
Interest Income Recognized	70	82	157	215
Impaired Loans With Related Allowance Recorded [Abstract]
Average Recorded Investment	220	1,288	161	4,108
Interest Income Recognized	11	0	12	0
Total [Abstract]
Average Recorded Investment	6,604	11,245	6,634	13,057
Interest Income Recognized	81	82	169	215
Multifamily [Member]
Impaired Loans With No Related Allowance Recorded [Abstract]
Average Recorded Investment	0	2,352	481	2,359
Interest Income Recognized	0	36	6	71
Total [Abstract]
Average Recorded Investment	0	2,352	481	2,359
Interest Income Recognized	0	36	6	71
Farmland [Member]
Impaired Loans With No Related Allowance Recorded [Abstract]
Average Recorded Investment	0	21	7	21
Interest Income Recognized	0	0	0	0
Total [Abstract]
Average Recorded Investment	0	21	7	21
Interest Income Recognized	0	0	0	0
Home equity lines [Member]
Impaired Loans With No Related Allowance Recorded [Abstract]
Average Recorded Investment	605	1,398	702	1,026
Interest Income Recognized	0	2	4	16
Total [Abstract]
Average Recorded Investment	605	1,398	702	1,026
Interest Income Recognized	0	2	4	16
Consumer Real Estate, Secured by 1-4 Family Residential [Member]
Impaired Loans With Related Allowance Recorded [Abstract]
Average Recorded Investment	1,510	1,955	1,525	2,059
Interest Income Recognized	0	5	0	5
First Deed of Trust [Member]
Impaired Loans With No Related Allowance Recorded [Abstract]
Average Recorded Investment	6,370	7,990	6,386	7,649
Interest Income Recognized	83	108	173	193
Impaired Loans With Related Allowance Recorded [Abstract]
Average Recorded Investment	1,259	1,848	1,272	1,951
Interest Income Recognized	0	2	0	2
Total [Abstract]
Average Recorded Investment	7,629	9,838	7,657	9,600
Interest Income Recognized	83	110	173	195
Second Deed of Trust [Member]
Impaired Loans With No Related Allowance Recorded [Abstract]
Average Recorded Investment	1,199	1,224	1,191	1,090
Interest Income Recognized	16	19	30	33
Impaired Loans With Related Allowance Recorded [Abstract]
Average Recorded Investment	251	107	253	108
Interest Income Recognized	0	3	0	3
Total [Abstract]
Average Recorded Investment	1,450	1,331	1,444	1,198
Interest Income Recognized	16	22	30	36
Consumer Real Estate [Member]
Impaired Loans With No Related Allowance Recorded [Abstract]
Average Recorded Investment	8,174	10,612	8,279	9,765
Interest Income Recognized	99	129	207	242
Total [Abstract]
Average Recorded Investment	9,684	12,567	9,803	11,824
Interest Income Recognized	99	134	207	247
Commercial and industrial loans (except those secured by real estate) [Member]
Impaired Loans With No Related Allowance Recorded [Abstract]
Average Recorded Investment	134	821	181	758
Interest Income Recognized	2	10	4	23
Impaired Loans With Related Allowance Recorded [Abstract]
Average Recorded Investment	421	115	457	116
Interest Income Recognized	11	0	16
Total [Abstract]
Average Recorded Investment	555	936	638	874
Interest Income Recognized	13	10	20	23
Consumer And Other [Member]
Impaired Loans With No Related Allowance Recorded [Abstract]
Average Recorded Investment	22	26	20	20
Interest Income Recognized	0	1	1	1
Total [Abstract]
Average Recorded Investment	22	26	20	20
Interest Income Recognized	$ 0	$ 1	$ 1	$ 1