Loans, Allowance for Loan Losses, and Credit Quality - Summary of loans by credit quality indicator based on internally assigned credit grade (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Financing Receivable, Recorded Investment [Line Items]
Total	$ 2,242,931	$ 2,166,181
Percent of total loans	100.00%	100.00%
Grades 1- 4
Financing Receivable, Recorded Investment [Line Items]
Total	$ 2,148,201	$ 2,061,424
Percent of total loans	95.80%	95.10%
Grade 5
Financing Receivable, Recorded Investment [Line Items]
Total	$ 49,539	$ 58,822
Percent of total loans	2.20%	2.70%
Grade 6
Financing Receivable, Recorded Investment [Line Items]
Total	$ 9,169	$ 18,607
Percent of total loans	0.40%	0.90%
Grade 7
Financing Receivable, Recorded Investment [Line Items]
Total	$ 36,022	$ 27,328
Percent of total loans	1.60%	1.30%
Grade 8
Financing Receivable, Recorded Investment [Line Items]
Total	$ 0	$ 0
Percent of total loans	0.00%	0.00%
Grade 9
Financing Receivable, Recorded Investment [Line Items]
Total	$ 0	$ 0
Percent of total loans	0.00%	0.00%
Retail & other
Financing Receivable, Recorded Investment [Line Items]
Total	$ 28,713	$ 26,493
Retail & other | Grades 1- 4
Financing Receivable, Recorded Investment [Line Items]
Total	28,705	26,493
Retail & other | Grade 5
Financing Receivable, Recorded Investment [Line Items]
Total	0	0
Retail & other | Grade 6
Financing Receivable, Recorded Investment [Line Items]
Total	0	0
Retail & other | Grade 7
Financing Receivable, Recorded Investment [Line Items]
Total	8	0
Retail & other | Grade 8
Financing Receivable, Recorded Investment [Line Items]
Total	0	0
Retail & other | Grade 9
Financing Receivable, Recorded Investment [Line Items]
Total	0	0
Commercial portfolio segment | Commercial & industrial
Financing Receivable, Recorded Investment [Line Items]
Total	763,742	684,920
Commercial portfolio segment | Commercial & industrial | Grades 1- 4
Financing Receivable, Recorded Investment [Line Items]
Total	725,484	649,475
Commercial portfolio segment | Commercial & industrial | Grade 5
Financing Receivable, Recorded Investment [Line Items]
Total	22,299	16,145
Commercial portfolio segment | Commercial & industrial | Grade 6
Financing Receivable, Recorded Investment [Line Items]
Total	2,076	6,178
Commercial portfolio segment | Commercial & industrial | Grade 7
Financing Receivable, Recorded Investment [Line Items]
Total	13,883	13,122
Commercial portfolio segment | Commercial & industrial | Grade 8
Financing Receivable, Recorded Investment [Line Items]
Total	0	0
Commercial portfolio segment | Commercial & industrial | Grade 9
Financing Receivable, Recorded Investment [Line Items]
Total	0	0
Commercial portfolio segment | Owner-occupied CRE
Financing Receivable, Recorded Investment [Line Items]
Total	456,508	441,353
Commercial portfolio segment | Owner-occupied CRE | Grades 1- 4
Financing Receivable, Recorded Investment [Line Items]
Total	428,332	405,198
Commercial portfolio segment | Owner-occupied CRE | Grade 5
Financing Receivable, Recorded Investment [Line Items]
Total	15,110	22,776
Commercial portfolio segment | Owner-occupied CRE | Grade 6
Financing Receivable, Recorded Investment [Line Items]
Total	963	6,569
Commercial portfolio segment | Owner-occupied CRE | Grade 7
Financing Receivable, Recorded Investment [Line Items]
Total	12,103	6,810
Commercial portfolio segment | Owner-occupied CRE | Grade 8
Financing Receivable, Recorded Investment [Line Items]
Total	0	0
Commercial portfolio segment | Owner-occupied CRE | Grade 9
Financing Receivable, Recorded Investment [Line Items]
Total	0	0
Commercial portfolio segment | AG production
Financing Receivable, Recorded Investment [Line Items]
Total	36,050	35,625
Commercial portfolio segment | AG production | Grades 1- 4
Financing Receivable, Recorded Investment [Line Items]
Total	27,350	29,363
Commercial portfolio segment | AG production | Grade 5
Financing Receivable, Recorded Investment [Line Items]
Total	4,044	3,302
Commercial portfolio segment | AG production | Grade 6
Financing Receivable, Recorded Investment [Line Items]
Total	1,669	2,351
Commercial portfolio segment | AG production | Grade 7
Financing Receivable, Recorded Investment [Line Items]
Total	2,987	609
Commercial portfolio segment | AG production | Grade 8
Financing Receivable, Recorded Investment [Line Items]
Total	0	0
Commercial portfolio segment | AG production | Grade 9
Financing Receivable, Recorded Investment [Line Items]
Total	0	0
Commercial real estate portfolio segment | AG real estate
Financing Receivable, Recorded Investment [Line Items]
Total	58,591	53,444
Commercial real estate portfolio segment | AG real estate | Grades 1- 4
Financing Receivable, Recorded Investment [Line Items]
Total	48,740	46,248
Commercial real estate portfolio segment | AG real estate | Grade 5
Financing Receivable, Recorded Investment [Line Items]
Total	4,077	3,246
Commercial real estate portfolio segment | AG real estate | Grade 6
Financing Receivable, Recorded Investment [Line Items]
Total	2,344	2,983
Commercial real estate portfolio segment | AG real estate | Grade 7
Financing Receivable, Recorded Investment [Line Items]
Total	3,430	967
Commercial real estate portfolio segment | AG real estate | Grade 8
Financing Receivable, Recorded Investment [Line Items]
Total	0	0
Commercial real estate portfolio segment | AG real estate | Grade 9
Financing Receivable, Recorded Investment [Line Items]
Total	0	0
Commercial real estate portfolio segment | CRE investment
Financing Receivable, Recorded Investment [Line Items]
Total	336,442	343,652
Commercial real estate portfolio segment | CRE investment | Grades 1- 4
Financing Receivable, Recorded Investment [Line Items]
Total	332,078	334,080
Commercial real estate portfolio segment | CRE investment | Grade 5
Financing Receivable, Recorded Investment [Line Items]
Total	2,345	6,792
Commercial real estate portfolio segment | CRE investment | Grade 6
Financing Receivable, Recorded Investment [Line Items]
Total	908	0
Commercial real estate portfolio segment | CRE investment | Grade 7
Financing Receivable, Recorded Investment [Line Items]
Total	1,111	2,780
Commercial real estate portfolio segment | CRE investment | Grade 8
Financing Receivable, Recorded Investment [Line Items]
Total	0	0
Commercial real estate portfolio segment | CRE investment | Grade 9
Financing Receivable, Recorded Investment [Line Items]
Total	0	0
Commercial real estate portfolio segment | Construction & land development
Financing Receivable, Recorded Investment [Line Items]
Total	61,810	80,599
Commercial real estate portfolio segment | Construction & land development | Grades 1- 4
Financing Receivable, Recorded Investment [Line Items]
Total	61,794	75,365
Commercial real estate portfolio segment | Construction & land development | Grade 5
Financing Receivable, Recorded Investment [Line Items]
Total	0	5,138
Commercial real estate portfolio segment | Construction & land development | Grade 6
Financing Receivable, Recorded Investment [Line Items]
Total	16	16
Commercial real estate portfolio segment | Construction & land development | Grade 7
Financing Receivable, Recorded Investment [Line Items]
Total	0	80
Commercial real estate portfolio segment | Construction & land development | Grade 8
Financing Receivable, Recorded Investment [Line Items]
Total	0	0
Commercial real estate portfolio segment | Construction & land development | Grade 9
Financing Receivable, Recorded Investment [Line Items]
Total	0	0
Residential | Residential first mortgage
Financing Receivable, Recorded Investment [Line Items]
Total	343,400	357,841
Residential | Residential first mortgage | Grades 1- 4
Financing Receivable, Recorded Investment [Line Items]
Total	338,627	353,239
Residential | Residential first mortgage | Grade 5
Financing Receivable, Recorded Investment [Line Items]
Total	1,664	1,406
Residential | Residential first mortgage | Grade 6
Financing Receivable, Recorded Investment [Line Items]
Total	1,193	510
Residential | Residential first mortgage | Grade 7
Financing Receivable, Recorded Investment [Line Items]
Total	1,916	2,686
Residential | Residential first mortgage | Grade 8
Financing Receivable, Recorded Investment [Line Items]
Total	0	0
Residential | Residential first mortgage | Grade 9
Financing Receivable, Recorded Investment [Line Items]
Total	0	0
Residential | Residential junior mortgage
Financing Receivable, Recorded Investment [Line Items]
Total	116,179	111,328
Residential | Residential junior mortgage | Grades 1- 4
Financing Receivable, Recorded Investment [Line Items]
Total	115,595	111,037
Residential | Residential junior mortgage | Grade 5
Financing Receivable, Recorded Investment [Line Items]
Total	0	17
Residential | Residential junior mortgage | Grade 6
Financing Receivable, Recorded Investment [Line Items]
Total	0	0
Residential | Residential junior mortgage | Grade 7
Financing Receivable, Recorded Investment [Line Items]
Total	584	274
Residential | Residential junior mortgage | Grade 8
Financing Receivable, Recorded Investment [Line Items]
Total	0	0
Residential | Residential junior mortgage | Grade 9
Financing Receivable, Recorded Investment [Line Items]
Total	0	0
Residential | Residential construction
Financing Receivable, Recorded Investment [Line Items]
Total	41,496	30,926
Residential | Residential construction | Grades 1- 4
Financing Receivable, Recorded Investment [Line Items]
Total	41,496	30,926
Residential | Residential construction | Grade 5
Financing Receivable, Recorded Investment [Line Items]
Total	0	0
Residential | Residential construction | Grade 6
Financing Receivable, Recorded Investment [Line Items]
Total	0	0
Residential | Residential construction | Grade 7
Financing Receivable, Recorded Investment [Line Items]
Total	0	0
Residential | Residential construction | Grade 8
Financing Receivable, Recorded Investment [Line Items]
Total	0	0
Residential | Residential construction | Grade 9
Financing Receivable, Recorded Investment [Line Items]
Total	$ 0	$ 0