Loans and allowance for loan losses (Details 5) $ in Thousands	6 Months Ended		12 Months Ended
	Jun. 30, 2015 USD ($) Loans	Jun. 30, 2014 Loans	Dec. 31, 2014 USD ($) Loans
Information concerning Troubled Debt Restructurings [Abstract]
Recorded Investment	$ 17,366		$ 27,141
Number of Loans | Loans	64	5	107
Construction and Land Development [Member]
Information concerning Troubled Debt Restructurings [Abstract]
Recorded Investment	$ 1,799		$ 3,902
Number of Loans | Loans	0	1
Owner Occupied [Member]
Information concerning Troubled Debt Restructurings [Abstract]
Recorded Investment	$ 5,823		6,317
Number of Loans | Loans	0	1
Non-Owner Occupied [Member]
Information concerning Troubled Debt Restructurings [Abstract]
Recorded Investment	$ 4,205		6,593
Number of Loans | Loans	0	1
Multifamily [Member]
Information concerning Troubled Debt Restructurings [Abstract]
Recorded Investment			2,322
Consumer Real Estate [Member]
Information concerning Troubled Debt Restructurings [Abstract]
Recorded Investment	$ 10,028		15,232
Consumer Real Estate, Secured by 1-4 Family Residential [Member]
Information concerning Troubled Debt Restructurings [Abstract]
Recorded Investment	$ 5,393		7,752
Number of Loans | Loans	0	2
First Deed of Trust [Member]
Information concerning Troubled Debt Restructurings [Abstract]
Recorded Investment	$ 4,647		6,990
Number of Loans | Loans	0	2
Second Deed of Trust [Member]
Information concerning Troubled Debt Restructurings [Abstract]
Recorded Investment	$ 746		762
Commercial and industrial loans (except those secured by real estate) [Member]
Information concerning Troubled Debt Restructurings [Abstract]
Recorded Investment	133		239
Consumer And Other [Member]
Information concerning Troubled Debt Restructurings [Abstract]
Recorded Investment	13		16
Residential [Member]
Information concerning Troubled Debt Restructurings [Abstract]
Recorded Investment			7
Commercial [Member]
Information concerning Troubled Debt Restructurings [Abstract]
Recorded Investment	$ 1,799		3,895
Number of Loans | Loans	0	1
Specific Valuation Allowance [Member]
Information concerning Troubled Debt Restructurings [Abstract]
Recorded Investment	$ 265		$ 0
Number of Loans | Loans	10		21
Specific Valuation Allowance [Member] | Construction and Land Development [Member]
Information concerning Troubled Debt Restructurings [Abstract]
Recorded Investment	$ 0		$ 17
Specific Valuation Allowance [Member] | Owner Occupied [Member]
Information concerning Troubled Debt Restructurings [Abstract]
Recorded Investment	128		325
Specific Valuation Allowance [Member] | Non-Owner Occupied [Member]
Information concerning Troubled Debt Restructurings [Abstract]
Recorded Investment	0		0
Specific Valuation Allowance [Member] | Multifamily [Member]
Information concerning Troubled Debt Restructurings [Abstract]
Recorded Investment			0
Specific Valuation Allowance [Member] | Consumer Real Estate [Member]
Information concerning Troubled Debt Restructurings [Abstract]
Recorded Investment	128		325
Specific Valuation Allowance [Member] | Consumer Real Estate, Secured by 1-4 Family Residential [Member]
Information concerning Troubled Debt Restructurings [Abstract]
Recorded Investment	$ 117		205
Specific Valuation Allowance [Member] | First Deed of Trust [Member]
Information concerning Troubled Debt Restructurings [Abstract]
Recorded Investment			200
Specific Valuation Allowance [Member] | Second Deed of Trust [Member]
Information concerning Troubled Debt Restructurings [Abstract]
Recorded Investment	$ 117		5
Specific Valuation Allowance [Member] | Commercial and industrial loans (except those secured by real estate) [Member]
Information concerning Troubled Debt Restructurings [Abstract]
Recorded Investment	20		12
Specific Valuation Allowance [Member] | Consumer And Other [Member]
Information concerning Troubled Debt Restructurings [Abstract]
Recorded Investment	0		0
Specific Valuation Allowance [Member] | Residential [Member]
Information concerning Troubled Debt Restructurings [Abstract]
Recorded Investment			0
Specific Valuation Allowance [Member] | Commercial [Member]
Information concerning Troubled Debt Restructurings [Abstract]
Recorded Investment	0		17
Performing Financing Receivable [Member]
Information concerning Troubled Debt Restructurings [Abstract]
Recorded Investment	$ 15,848		$ 0
Number of Loans | Loans	43		77
Performing Financing Receivable [Member] | Construction and Land Development [Member]
Information concerning Troubled Debt Restructurings [Abstract]
Recorded Investment	$ 1,708		$ 3,751
Performing Financing Receivable [Member] | Owner Occupied [Member]
Information concerning Troubled Debt Restructurings [Abstract]
Recorded Investment	5,522		5,149
Performing Financing Receivable [Member] | Non-Owner Occupied [Member]
Information concerning Troubled Debt Restructurings [Abstract]
Recorded Investment	4,205		6,593
Performing Financing Receivable [Member] | Multifamily [Member]
Information concerning Troubled Debt Restructurings [Abstract]
Recorded Investment			2,322
Performing Financing Receivable [Member] | Consumer Real Estate [Member]
Information concerning Troubled Debt Restructurings [Abstract]
Recorded Investment	9,727		14,064
Performing Financing Receivable [Member] | Consumer Real Estate, Secured by 1-4 Family Residential [Member]
Information concerning Troubled Debt Restructurings [Abstract]
Recorded Investment	4,413		6,152
Performing Financing Receivable [Member] | First Deed of Trust [Member]
Information concerning Troubled Debt Restructurings [Abstract]
Recorded Investment	4,045		5,494
Performing Financing Receivable [Member] | Second Deed of Trust [Member]
Information concerning Troubled Debt Restructurings [Abstract]
Recorded Investment	368		658
Performing Financing Receivable [Member] | Commercial and industrial loans (except those secured by real estate) [Member]
Information concerning Troubled Debt Restructurings [Abstract]
Recorded Investment	0		0
Performing Financing Receivable [Member] | Consumer And Other [Member]
Information concerning Troubled Debt Restructurings [Abstract]
Recorded Investment	0		0
Performing Financing Receivable [Member] | Residential [Member]
Information concerning Troubled Debt Restructurings [Abstract]
Recorded Investment			0
Performing Financing Receivable [Member] | Commercial [Member]
Information concerning Troubled Debt Restructurings [Abstract]
Recorded Investment	1,708		3,751
Nonperforming Financing Receivable [Member]
Information concerning Troubled Debt Restructurings [Abstract]
Recorded Investment	$ 1,518		$ 0
Number of Loans | Loans	21		30
Nonperforming Financing Receivable [Member] | Construction and Land Development [Member]
Information concerning Troubled Debt Restructurings [Abstract]
Recorded Investment	$ 91		$ 151
Nonperforming Financing Receivable [Member] | Owner Occupied [Member]
Information concerning Troubled Debt Restructurings [Abstract]
Recorded Investment	301		1,168
Nonperforming Financing Receivable [Member] | Non-Owner Occupied [Member]
Information concerning Troubled Debt Restructurings [Abstract]
Recorded Investment	0		0
Nonperforming Financing Receivable [Member] | Multifamily [Member]
Information concerning Troubled Debt Restructurings [Abstract]
Recorded Investment			0
Nonperforming Financing Receivable [Member] | Consumer Real Estate [Member]
Information concerning Troubled Debt Restructurings [Abstract]
Recorded Investment	301		1,168
Nonperforming Financing Receivable [Member] | Consumer Real Estate, Secured by 1-4 Family Residential [Member]
Information concerning Troubled Debt Restructurings [Abstract]
Recorded Investment	980		1,600
Nonperforming Financing Receivable [Member] | First Deed of Trust [Member]
Information concerning Troubled Debt Restructurings [Abstract]
Recorded Investment	602		1,496
Nonperforming Financing Receivable [Member] | Second Deed of Trust [Member]
Information concerning Troubled Debt Restructurings [Abstract]
Recorded Investment	378		104
Nonperforming Financing Receivable [Member] | Commercial and industrial loans (except those secured by real estate) [Member]
Information concerning Troubled Debt Restructurings [Abstract]
Recorded Investment	133		239
Nonperforming Financing Receivable [Member] | Consumer And Other [Member]
Information concerning Troubled Debt Restructurings [Abstract]
Recorded Investment	13		16
Nonperforming Financing Receivable [Member] | Residential [Member]
Information concerning Troubled Debt Restructurings [Abstract]
Recorded Investment			7
Nonperforming Financing Receivable [Member] | Commercial [Member]
Information concerning Troubled Debt Restructurings [Abstract]
Recorded Investment	$ 91		$ 144