Loans, Allowance for Credit Losses - Loans, and Credit Quality - Collateral dependent loans by portfolio segment (Details) $ in Thousands	Mar. 31, 2020 USD ($)
Financing Receivable, Allowance for Credit Loss [Line Items]
Loans	$ 11,806
Without an Allowance	6,371
With an Allowance	5,435
Allowance Allocation	1,744
Real Estate
Financing Receivable, Allowance for Credit Loss [Line Items]
Loans	5,341
Other Business Assets
Financing Receivable, Allowance for Credit Loss [Line Items]
Loans	6,465
Retail & other
Financing Receivable, Allowance for Credit Loss [Line Items]
Loans	0
Without an Allowance	0
With an Allowance	0
Allowance Allocation	0
Retail & other | Real Estate
Financing Receivable, Allowance for Credit Loss [Line Items]
Loans	0
Retail & other | Other Business Assets
Financing Receivable, Allowance for Credit Loss [Line Items]
Loans	0
Commercial portfolio segment | Commercial & industrial
Financing Receivable, Allowance for Credit Loss [Line Items]
Loans	5,544
Without an Allowance	978
With an Allowance	4,566
Allowance Allocation	1,683
Commercial portfolio segment | Commercial & industrial | Real Estate
Financing Receivable, Allowance for Credit Loss [Line Items]
Loans	0
Commercial portfolio segment | Commercial & industrial | Other Business Assets
Financing Receivable, Allowance for Credit Loss [Line Items]
Loans	5,544
Commercial portfolio segment | Owner-occupied CRE
Financing Receivable, Allowance for Credit Loss [Line Items]
Loans	3,168
Without an Allowance	3,168
With an Allowance	0
Allowance Allocation	0
Commercial portfolio segment | Owner-occupied CRE | Real Estate
Financing Receivable, Allowance for Credit Loss [Line Items]
Loans	3,168
Commercial portfolio segment | Owner-occupied CRE | Other Business Assets
Financing Receivable, Allowance for Credit Loss [Line Items]
Loans	0
Commercial portfolio segment | Agricultural
Financing Receivable, Allowance for Credit Loss [Line Items]
Loans	1,532
Without an Allowance	663
With an Allowance	869
Allowance Allocation	61
Commercial portfolio segment | Agricultural | Real Estate
Financing Receivable, Allowance for Credit Loss [Line Items]
Loans	611
Commercial portfolio segment | Agricultural | Other Business Assets
Financing Receivable, Allowance for Credit Loss [Line Items]
Loans	921
Commercial real estate portfolio segment | CRE investment
Financing Receivable, Allowance for Credit Loss [Line Items]
Loans	1,029
Without an Allowance	1,029
With an Allowance	0
Allowance Allocation	0
Commercial real estate portfolio segment | CRE investment | Real Estate
Financing Receivable, Allowance for Credit Loss [Line Items]
Loans	1,029
Commercial real estate portfolio segment | CRE investment | Other Business Assets
Financing Receivable, Allowance for Credit Loss [Line Items]
Loans	0
Commercial real estate portfolio segment | Construction & land development
Financing Receivable, Allowance for Credit Loss [Line Items]
Loans	533
Without an Allowance	533
With an Allowance	0
Allowance Allocation	0
Commercial real estate portfolio segment | Construction & land development | Real Estate
Financing Receivable, Allowance for Credit Loss [Line Items]
Loans	533
Commercial real estate portfolio segment | Construction & land development | Other Business Assets
Financing Receivable, Allowance for Credit Loss [Line Items]
Loans	0
Residential | Residential construction
Financing Receivable, Allowance for Credit Loss [Line Items]
Loans	0
Without an Allowance	0
With an Allowance	0
Allowance Allocation	0
Residential | Residential construction | Real Estate
Financing Receivable, Allowance for Credit Loss [Line Items]
Loans	0
Residential | Residential construction | Other Business Assets
Financing Receivable, Allowance for Credit Loss [Line Items]
Loans	0
Residential first mortgage | Residential
Financing Receivable, Allowance for Credit Loss [Line Items]
Loans	0
Without an Allowance	0
With an Allowance	0
Allowance Allocation	0
Residential first mortgage | Residential | Real Estate
Financing Receivable, Allowance for Credit Loss [Line Items]
Loans	0
Residential first mortgage | Residential | Other Business Assets
Financing Receivable, Allowance for Credit Loss [Line Items]
Loans	0
Residential junior mortgage | Residential
Financing Receivable, Allowance for Credit Loss [Line Items]
Loans	0
Without an Allowance	0
With an Allowance	0
Allowance Allocation	0
Residential junior mortgage | Residential | Real Estate
Financing Receivable, Allowance for Credit Loss [Line Items]
Loans	0
Residential junior mortgage | Residential | Other Business Assets
Financing Receivable, Allowance for Credit Loss [Line Items]
Loans	$ 0