Loans, Allowance for Loan Losses, and Credit Quality - Nonaccrual loans by portfolio segment (Details 3) - Loans Receivable - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014
Accounts, Notes, Loans and Financing Receivable [Line Items]
Nonaccrual loans	$ 4,247	$ 5,392
% to Non Accrual Total	1.00%	1.00%
Commercial & industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Nonaccrual loans	$ 324	$ 171
% to Non Accrual Total	7.60%	3.20%
Owner-occupied CRE
Accounts, Notes, Loans and Financing Receivable [Line Items]
Nonaccrual loans	$ 813	$ 1,667
% to Non Accrual Total	19.10%	30.90%
AG Production
Accounts, Notes, Loans and Financing Receivable [Line Items]
Nonaccrual loans	$ 16	$ 21
% to Non Accrual Total	0.40%	0.40%
AG real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Nonaccrual loans	$ 383	$ 392
% to Non Accrual Total	9.00%	7.30%
CRE investment
Accounts, Notes, Loans and Financing Receivable [Line Items]
Nonaccrual loans	$ 738	$ 911
% to Non Accrual Total	17.40%	16.90%
Construction & land development
Accounts, Notes, Loans and Financing Receivable [Line Items]
Nonaccrual loans	$ 709	$ 934
% to Non Accrual Total	16.70%	17.30%
Residential construction
Accounts, Notes, Loans and Financing Receivable [Line Items]
Nonaccrual loans
% to Non Accrual Total
Residential first mortgage
Accounts, Notes, Loans and Financing Receivable [Line Items]
Nonaccrual loans	$ 1,112	$ 1,155
% to Non Accrual Total	26.20%	21.40%
Residential junior mortgage
Accounts, Notes, Loans and Financing Receivable [Line Items]
Nonaccrual loans	$ 152	$ 141
% to Non Accrual Total	3.60%	2.60%
Retail & other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Nonaccrual loans
% to Non Accrual Total
Originated
Accounts, Notes, Loans and Financing Receivable [Line Items]
Nonaccrual loans	$ 477	$ 1,128
% to Non Accrual Total	100.00%	100.00%
Originated | Commercial & industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Nonaccrual loans	$ 292	$ 130
% to Non Accrual Total	61.20%	11.50%
Originated | Owner-occupied CRE
Accounts, Notes, Loans and Financing Receivable [Line Items]
Nonaccrual loans	$ 13	$ 673
% to Non Accrual Total	2.70%	59.70%
Originated | AG Production
Accounts, Notes, Loans and Financing Receivable [Line Items]
Nonaccrual loans	$ 16
% to Non Accrual Total	3.40%
Originated | AG real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Nonaccrual loans
% to Non Accrual Total
Originated | CRE investment
Accounts, Notes, Loans and Financing Receivable [Line Items]
Nonaccrual loans
% to Non Accrual Total
Originated | Construction & land development
Accounts, Notes, Loans and Financing Receivable [Line Items]
Nonaccrual loans		$ 165
% to Non Accrual Total		14.60%
Originated | Residential construction
Accounts, Notes, Loans and Financing Receivable [Line Items]
Nonaccrual loans
% to Non Accrual Total
Originated | Residential first mortgage
Accounts, Notes, Loans and Financing Receivable [Line Items]
Nonaccrual loans	$ 156	$ 160
% to Non Accrual Total	32.70%	14.20%
Originated | Residential junior mortgage
Accounts, Notes, Loans and Financing Receivable [Line Items]
Nonaccrual loans
% to Non Accrual Total
Originated | Retail & other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Nonaccrual loans
% to Non Accrual Total
Acquired
Accounts, Notes, Loans and Financing Receivable [Line Items]
Nonaccrual loans	$ 3,770	$ 4,264
% to Non Accrual Total	100.00%	100.00%
Acquired | Commercial & industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Nonaccrual loans	$ 32	$ 41
% to Non Accrual Total	0.80%	1.00%
Acquired | Owner-occupied CRE
Accounts, Notes, Loans and Financing Receivable [Line Items]
Nonaccrual loans	$ 800	$ 994
% to Non Accrual Total	21.20%	23.30%
Acquired | AG Production
Accounts, Notes, Loans and Financing Receivable [Line Items]
Nonaccrual loans		$ 21
% to Non Accrual Total		0.50%
Acquired | AG real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Nonaccrual loans	$ 383	$ 392
% to Non Accrual Total	10.20%	9.20%
Acquired | CRE investment
Accounts, Notes, Loans and Financing Receivable [Line Items]
Nonaccrual loans	$ 738	$ 911
% to Non Accrual Total	19.60%	21.40%
Acquired | Construction & land development
Accounts, Notes, Loans and Financing Receivable [Line Items]
Nonaccrual loans	$ 709	$ 769
% to Non Accrual Total	18.80%	18.00%
Acquired | Residential construction
Accounts, Notes, Loans and Financing Receivable [Line Items]
Nonaccrual loans
% to Non Accrual Total
Acquired | Residential first mortgage
Accounts, Notes, Loans and Financing Receivable [Line Items]
Nonaccrual loans	$ 956	$ 995
% to Non Accrual Total	25.40%	23.30%
Acquired | Residential junior mortgage
Accounts, Notes, Loans and Financing Receivable [Line Items]
Nonaccrual loans	$ 152	$ 141
% to Non Accrual Total	4.00%	3.30%
Acquired | Retail & other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Nonaccrual loans
% to Non Accrual Total