Loans, Allowance for Credit Losses - Loans, and Credit Quality - Summary of loans by loan risk categories (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Financing Receivable, Credit Quality Indicator [Line Items]
Origination Year - 2020	$ 746,014
Origination Year - 2019	442,066
Origination Year - 2018	323,551
Origination Year - 2017	288,238
Origination Year - 2016	172,428
Origination Year - Prior	584,886
Revolving	350,132
Revolving to Term	1,478
Total	$ 2,908,793	$ 2,573,751
Percent of total	100.00%	100.00%
Grades 1- 4
Financing Receivable, Credit Quality Indicator [Line Items]
Total	$ 2,785,676	$ 2,457,922
Percent of total	95.80%	95.50%
Grade 5
Financing Receivable, Credit Quality Indicator [Line Items]
Total	$ 69,848	$ 63,966
Percent of total	2.40%	2.50%
Grade 6
Financing Receivable, Credit Quality Indicator [Line Items]
Total	$ 15,192	$ 15,152
Percent of total	0.50%	0.60%
Grade 7
Financing Receivable, Credit Quality Indicator [Line Items]
Total	$ 38,077	$ 36,711
Percent of total	1.30%	1.40%
Retail & other
Financing Receivable, Credit Quality Indicator [Line Items]
Origination Year - 2020	$ 7,693
Origination Year - 2019	6,027
Origination Year - 2018	2,208
Origination Year - 2017	1,808
Origination Year - 2016	876
Origination Year - Prior	1,565
Revolving	12,839
Revolving to Term	0
Total	33,016	$ 30,211
Retail & other \| Grades 1- 4
Financing Receivable, Credit Quality Indicator [Line Items]
Origination Year - 2020	7,693
Origination Year - 2019	6,027
Origination Year - 2018	2,208
Origination Year - 2017	1,808
Origination Year - 2016	876
Origination Year - Prior	1,514
Revolving	12,839
Revolving to Term	0
Total	32,965	30,210
Retail & other \| Grade 5
Financing Receivable, Credit Quality Indicator [Line Items]
Origination Year - 2020	0
Origination Year - 2019	0
Origination Year - 2018	0
Origination Year - 2017	0
Origination Year - 2016	0
Origination Year - Prior	0
Revolving	0
Revolving to Term	0
Total	0	0
Retail & other \| Grade 6
Financing Receivable, Credit Quality Indicator [Line Items]
Origination Year - 2020	0
Origination Year - 2019	0
Origination Year - 2018	0
Origination Year - 2017	0
Origination Year - 2016	0
Origination Year - Prior	0
Revolving	0
Revolving to Term	0
Total	0	0
Retail & other \| Grade 7
Financing Receivable, Credit Quality Indicator [Line Items]
Origination Year - 2020	0
Origination Year - 2019	0
Origination Year - 2018	0
Origination Year - 2017	0
Origination Year - 2016	0
Origination Year - Prior	51
Revolving	0
Revolving to Term	0
Total	51	1
Commercial portfolio segment \| Commercial & industrial
Financing Receivable, Credit Quality Indicator [Line Items]
Origination Year - 2020	432,199
Origination Year - 2019	140,013
Origination Year - 2018	113,623
Origination Year - 2017	85,111
Origination Year - 2016	28,272
Origination Year - Prior	62,598
Revolving	208,951
Revolving to Term	0
Total	1,070,767
Commercial portfolio segment \| Commercial & industrial \| Grades 1- 4
Financing Receivable, Credit Quality Indicator [Line Items]
Origination Year - 2020	429,518
Origination Year - 2019	135,539
Origination Year - 2018	107,712
Origination Year - 2017	78,205
Origination Year - 2016	26,209
Origination Year - Prior	55,141
Revolving	188,738
Revolving to Term	0
Total	1,021,062
Commercial portfolio segment \| Commercial & industrial \| Grade 5
Financing Receivable, Credit Quality Indicator [Line Items]
Origination Year - 2020	649
Origination Year - 2019	3,300
Origination Year - 2018	3,584
Origination Year - 2017	588
Origination Year - 2016	1,427
Origination Year - Prior	2,483
Revolving	15,098
Revolving to Term	0
Total	27,129
Commercial portfolio segment \| Commercial & industrial \| Grade 6
Financing Receivable, Credit Quality Indicator [Line Items]
Origination Year - 2020	73
Origination Year - 2019	21
Origination Year - 2018	765
Origination Year - 2017	5,604
Origination Year - 2016	176
Origination Year - Prior	33
Revolving	2,405
Revolving to Term	0
Total	9,077
Commercial portfolio segment \| Commercial & industrial \| Grade 7
Financing Receivable, Credit Quality Indicator [Line Items]
Origination Year - 2020	1,959
Origination Year - 2019	1,153
Origination Year - 2018	1,562
Origination Year - 2017	714
Origination Year - 2016	460
Origination Year - Prior	4,941
Revolving	2,710
Revolving to Term	0
Total	13,499
Commercial portfolio segment \| Commercial & industrial
Financing Receivable, Credit Quality Indicator [Line Items]
Total	735,531	806,189
Commercial portfolio segment \| Commercial & industrial \| Grades 1- 4
Financing Receivable, Credit Quality Indicator [Line Items]
Total	685,826	765,073
Commercial portfolio segment \| Commercial & industrial \| Grade 5
Financing Receivable, Credit Quality Indicator [Line Items]
Total	27,129	20,199
Commercial portfolio segment \| Commercial & industrial \| Grade 6
Financing Receivable, Credit Quality Indicator [Line Items]
Total	9,077	7,663
Commercial portfolio segment \| Commercial & industrial \| Grade 7
Financing Receivable, Credit Quality Indicator [Line Items]
Total	13,499	13,254
Commercial portfolio segment \| Owner-occupied commercial real estate (“CRE”)
Financing Receivable, Credit Quality Indicator [Line Items]
Origination Year - 2020	52,667
Origination Year - 2019	68,881
Origination Year - 2018	84,073
Origination Year - 2017	67,567
Origination Year - 2016	49,375
Origination Year - Prior	174,757
Revolving	2,285
Revolving to Term	0
Total	499,605	496,372
Commercial portfolio segment \| Owner-occupied commercial real estate (“CRE”) \| Grades 1- 4
Financing Receivable, Credit Quality Indicator [Line Items]
Origination Year - 2020	52,625
Origination Year - 2019	67,705
Origination Year - 2018	82,734
Origination Year - 2017	56,258
Origination Year - 2016	47,267
Origination Year - Prior	160,406
Revolving	1,796
Revolving to Term	0
Total	468,791	464,661
Commercial portfolio segment \| Owner-occupied commercial real estate (“CRE”) \| Grade 5
Financing Receivable, Credit Quality Indicator [Line Items]
Origination Year - 2020	42
Origination Year - 2019	842
Origination Year - 2018	1,060
Origination Year - 2017	7,416
Origination Year - 2016	361
Origination Year - Prior	6,883
Revolving	489
Revolving to Term	0
Total	17,093	20,855
Commercial portfolio segment \| Owner-occupied commercial real estate (“CRE”) \| Grade 6
Financing Receivable, Credit Quality Indicator [Line Items]
Origination Year - 2020	0
Origination Year - 2019	0
Origination Year - 2018	0
Origination Year - 2017	1,723
Origination Year - 2016	0
Origination Year - Prior	729
Revolving	0
Revolving to Term	0
Total	2,452	953
Commercial portfolio segment \| Owner-occupied commercial real estate (“CRE”) \| Grade 7
Financing Receivable, Credit Quality Indicator [Line Items]
Origination Year - 2020	0
Origination Year - 2019	334
Origination Year - 2018	279
Origination Year - 2017	2,170
Origination Year - 2016	1,747
Origination Year - Prior	6,739
Revolving	0
Revolving to Term	0
Total	11,269	9,903
Commercial portfolio segment \| Agricultural
Financing Receivable, Credit Quality Indicator [Line Items]
Origination Year - 2020	11,987
Origination Year - 2019	6,513
Origination Year - 2018	8,845
Origination Year - 2017	10,337
Origination Year - 2016	5,244
Origination Year - Prior	44,537
Revolving	23,559
Revolving to Term	0
Total	111,022	95,450
Commercial portfolio segment \| Agricultural \| Grades 1- 4
Financing Receivable, Credit Quality Indicator [Line Items]
Origination Year - 2020	11,683
Origination Year - 2019	6,138
Origination Year - 2018	8,095
Origination Year - 2017	9,328
Origination Year - 2016	3,046
Origination Year - Prior	33,620
Revolving	22,828
Revolving to Term	0
Total	94,738	77,082
Commercial portfolio segment \| Agricultural \| Grade 5
Financing Receivable, Credit Quality Indicator [Line Items]
Origination Year - 2020	304
Origination Year - 2019	375
Origination Year - 2018	717
Origination Year - 2017	570
Origination Year - 2016	667
Origination Year - Prior	5,374
Revolving	683
Revolving to Term	0
Total	8,690	6,785
Commercial portfolio segment \| Agricultural \| Grade 6
Financing Receivable, Credit Quality Indicator [Line Items]
Origination Year - 2020	0
Origination Year - 2019	0
Origination Year - 2018	0
Origination Year - 2017	328
Origination Year - 2016	392
Origination Year - Prior	0
Revolving	0
Revolving to Term	0
Total	720	3,275
Commercial portfolio segment \| Agricultural \| Grade 7
Financing Receivable, Credit Quality Indicator [Line Items]
Origination Year - 2020	0
Origination Year - 2019	0
Origination Year - 2018	33
Origination Year - 2017	111
Origination Year - 2016	1,139
Origination Year - Prior	5,543
Revolving	48
Revolving to Term	0
Total	6,874	8,308
Commercial portfolio segment \| PPP loans
Financing Receivable, Credit Quality Indicator [Line Items]
Total	335,236	0
Commercial portfolio segment \| PPP loans \| Grades 1- 4
Financing Receivable, Credit Quality Indicator [Line Items]
Total	335,236
Commercial portfolio segment \| PPP loans \| Grade 5
Financing Receivable, Credit Quality Indicator [Line Items]
Total	0
Commercial portfolio segment \| PPP loans \| Grade 6
Financing Receivable, Credit Quality Indicator [Line Items]
Total	0
Commercial portfolio segment \| PPP loans \| Grade 7
Financing Receivable, Credit Quality Indicator [Line Items]
Total	0
Commercial real estate portfolio segment \| CRE investment
Financing Receivable, Credit Quality Indicator [Line Items]
Origination Year - 2020	67,988
Origination Year - 2019	81,913
Origination Year - 2018	44,148
Origination Year - 2017	71,784
Origination Year - 2016	36,966
Origination Year - Prior	165,509
Revolving	6,742
Revolving to Term	0
Total	475,050	443,218
Commercial real estate portfolio segment \| CRE investment \| Grades 1- 4
Financing Receivable, Credit Quality Indicator [Line Items]
Origination Year - 2020	67,988
Origination Year - 2019	81,809
Origination Year - 2018	44,047
Origination Year - 2017	69,685
Origination Year - 2016	35,332
Origination Year - Prior	156,073
Revolving	6,742
Revolving to Term	0
Total	461,676	430,794
Commercial real estate portfolio segment \| CRE investment \| Grade 5
Financing Receivable, Credit Quality Indicator [Line Items]
Origination Year - 2020	0
Origination Year - 2019	0
Origination Year - 2018	101
Origination Year - 2017	1,295
Origination Year - 2016	840
Origination Year - Prior	5,636
Revolving	0
Revolving to Term	0
Total	7,872	8,085
Commercial real estate portfolio segment \| CRE investment \| Grade 6
Financing Receivable, Credit Quality Indicator [Line Items]
Origination Year - 2020	0
Origination Year - 2019	104
Origination Year - 2018	0
Origination Year - 2017	804
Origination Year - 2016	652
Origination Year - Prior	1,122
Revolving	0
Revolving to Term	0
Total	2,682	2,578
Commercial real estate portfolio segment \| CRE investment \| Grade 7
Financing Receivable, Credit Quality Indicator [Line Items]
Origination Year - 2020	0
Origination Year - 2019	0
Origination Year - 2018	0
Origination Year - 2017	0
Origination Year - 2016	142
Origination Year - Prior	2,678
Revolving	0
Revolving to Term	0
Total	2,820	1,761
Commercial real estate portfolio segment \| Construction & land development
Financing Receivable, Credit Quality Indicator [Line Items]
Origination Year - 2020	46,088
Origination Year - 2019	36,977
Origination Year - 2018	18,256
Origination Year - 2017	3,612
Origination Year - 2016	2,192
Origination Year - Prior	9,854
Revolving	4,668
Revolving to Term	0
Total	121,647	92,970
Commercial real estate portfolio segment \| Construction & land development \| Grades 1- 4
Financing Receivable, Credit Quality Indicator [Line Items]
Origination Year - 2020	46,088
Origination Year - 2019	36,507
Origination Year - 2018	15,573
Origination Year - 2017	3,067
Origination Year - 2016	2,192
Origination Year - Prior	8,930
Revolving	4,211
Revolving to Term	0
Total	116,568	90,523
Commercial real estate portfolio segment \| Construction & land development \| Grade 5
Financing Receivable, Credit Quality Indicator [Line Items]
Origination Year - 2020	0
Origination Year - 2019	470
Origination Year - 2018	2,683
Origination Year - 2017	545
Origination Year - 2016	0
Origination Year - Prior	24
Revolving	457
Revolving to Term	0
Total	4,179	2,213
Commercial real estate portfolio segment \| Construction & land development \| Grade 6
Financing Receivable, Credit Quality Indicator [Line Items]
Origination Year - 2020	0
Origination Year - 2019	0
Origination Year - 2018	0
Origination Year - 2017	0
Origination Year - 2016	0
Origination Year - Prior	0
Revolving	0
Revolving to Term	0
Total	0	15
Commercial real estate portfolio segment \| Construction & land development \| Grade 7
Financing Receivable, Credit Quality Indicator [Line Items]
Origination Year - 2020	0
Origination Year - 2019	0
Origination Year - 2018	0
Origination Year - 2017	0
Origination Year - 2016	0
Origination Year - Prior	900
Revolving	0
Revolving to Term	0
Total	900	219
Residential \| Residential construction
Financing Receivable, Credit Quality Indicator [Line Items]
Origination Year - 2020	29,372
Origination Year - 2019	26,354
Origination Year - 2018	1,216
Origination Year - 2017	504
Origination Year - 2016	0
Origination Year - Prior	50
Revolving	0
Revolving to Term	0
Total	57,496	54,403
Residential \| Residential construction \| Grades 1- 4
Financing Receivable, Credit Quality Indicator [Line Items]
Origination Year - 2020	29,372
Origination Year - 2019	26,039
Origination Year - 2018	1,216
Origination Year - 2017	449
Origination Year - 2016	0
Origination Year - Prior	50
Revolving	0
Revolving to Term	0
Total	57,126	53,286
Residential \| Residential construction \| Grade 5
Financing Receivable, Credit Quality Indicator [Line Items]
Origination Year - 2020	0
Origination Year - 2019	315
Origination Year - 2018	0
Origination Year - 2017	55
Origination Year - 2016	0
Origination Year - Prior	0
Revolving	0
Revolving to Term	0
Total	370	1,117
Residential \| Residential construction \| Grade 6
Financing Receivable, Credit Quality Indicator [Line Items]
Origination Year - 2020	0
Origination Year - 2019	0
Origination Year - 2018	0
Origination Year - 2017	0
Origination Year - 2016	0
Origination Year - Prior	0
Revolving	0
Revolving to Term	0
Total	0	0
Residential \| Residential construction \| Grade 7
Financing Receivable, Credit Quality Indicator [Line Items]
Origination Year - 2020	0
Origination Year - 2019	0
Origination Year - 2018	0
Origination Year - 2017	0
Origination Year - 2016	0
Origination Year - Prior	0
Revolving	0
Revolving to Term	0
Total	0	0
Residential \| Residential first mortgage
Financing Receivable, Credit Quality Indicator [Line Items]
Origination Year - 2020	94,370
Origination Year - 2019	70,775
Origination Year - 2018	46,792
Origination Year - 2017	46,012
Origination Year - 2016	47,773
Origination Year - Prior	121,931
Revolving	364
Revolving to Term	0
Total	428,017	432,167
Residential \| Residential first mortgage \| Grades 1- 4
Financing Receivable, Credit Quality Indicator [Line Items]
Origination Year - 2020	94,370
Origination Year - 2019	69,301
Origination Year - 2018	45,425
Origination Year - 2017	45,798
Origination Year - 2016	47,449
Origination Year - Prior	118,317
Revolving	364
Revolving to Term	0
Total	421,024	424,044
Residential \| Residential first mortgage \| Grade 5
Financing Receivable, Credit Quality Indicator [Line Items]
Origination Year - 2020	0
Origination Year - 2019	821
Origination Year - 2018	908
Origination Year - 2017	197
Origination Year - 2016	324
Origination Year - Prior	2,232
Revolving	0
Revolving to Term	0
Total	4,482	4,677
Residential \| Residential first mortgage \| Grade 6
Financing Receivable, Credit Quality Indicator [Line Items]
Origination Year - 2020	0
Origination Year - 2019	0
Origination Year - 2018	261
Origination Year - 2017	0
Origination Year - 2016	0
Origination Year - Prior	0
Revolving	0
Revolving to Term	0
Total	261	668
Residential \| Residential first mortgage \| Grade 7
Financing Receivable, Credit Quality Indicator [Line Items]
Origination Year - 2020	0
Origination Year - 2019	653
Origination Year - 2018	198
Origination Year - 2017	17
Origination Year - 2016	0
Origination Year - Prior	1,382
Revolving	0
Revolving to Term	0
Total	2,250	2,778
Residential \| Residential junior mortgage
Financing Receivable, Credit Quality Indicator [Line Items]
Origination Year - 2020	3,650

Loans, Allowance for Credit Losses - Loans, and Credit Quality - Summary of loans by loan risk categories (Details) - USD ($)
$ in Thousands

Sep. 30, 2020

Dec. 31, 2019

Financing Receivable, Credit Quality Indicator [Line Items]

Origination Year - 2020

$ 746,014

Origination Year - 2019

442,066

Origination Year - 2018

323,551

Origination Year - 2017

288,238