Loans, Allowance for Credit Losses - Loans, and Credit Quality - Summary of loans by loan risk categories (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Financing Receivable, Credit Quality Indicator [Line Items]
Origination Year - 2020	$ 589,200
Origination Year - 2019	469,044
Origination Year - 2018	334,235
Origination Year - 2017	292,819
Origination Year - 2016	185,993
Origination Year - Prior	602,753
Revolving	345,788
Revolving to Term	1,669
Total	$ 2,821,501	$ 2,573,751
Percent of total	100.00%	100.00%
Grades 1- 4
Financing Receivable, Credit Quality Indicator [Line Items]
Total	$ 2,687,636	$ 2,457,922
Percent of total	95.20%	95.50%
Grade 5
Financing Receivable, Credit Quality Indicator [Line Items]
Total	$ 75,378	$ 63,966
Percent of total	2.70%	2.50%
Grade 6
Financing Receivable, Credit Quality Indicator [Line Items]
Total	$ 16,701	$ 15,152
Percent of total	0.60%	0.60%
Grade 7
Financing Receivable, Credit Quality Indicator [Line Items]
Total	$ 41,786	$ 36,711
Percent of total	1.50%	1.40%
Retail & other
Financing Receivable, Credit Quality Indicator [Line Items]
Origination Year - 2020	$ 5,090
Origination Year - 2019	6,205
Origination Year - 2018	2,403
Origination Year - 2017	1,869
Origination Year - 2016	941
Origination Year - Prior	1,522
Revolving	11,782
Revolving to Term	0
Total	29,812	$ 30,211
Retail & other \| Grades 1- 4
Financing Receivable, Credit Quality Indicator [Line Items]
Origination Year - 2020	5,090
Origination Year - 2019	6,205
Origination Year - 2018	2,403
Origination Year - 2017	1,869
Origination Year - 2016	941
Origination Year - Prior	1,522
Revolving	11,782
Revolving to Term	0
Total	29,812	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	0
Revolving	0
Revolving to Term	0
Total	0	1
Commercial portfolio segment \| Commercial & industrial
Financing Receivable, Credit Quality Indicator [Line Items]
Origination Year - 2020	399,589
Origination Year - 2019	156,822
Origination Year - 2018	119,210
Origination Year - 2017	76,394
Origination Year - 2016	30,818
Origination Year - Prior	67,248
Revolving	208,340
Revolving to Term	0
Total	1,058,421
Commercial portfolio segment \| Commercial & industrial \| Grades 1- 4
Financing Receivable, Credit Quality Indicator [Line Items]
Origination Year - 2020	397,577
Origination Year - 2019	150,186
Origination Year - 2018	109,524
Origination Year - 2017	68,689
Origination Year - 2016	28,748
Origination Year - Prior	58,379
Revolving	183,671
Revolving to Term	0
Total	996,774
Commercial portfolio segment \| Commercial & industrial \| Grade 5
Financing Receivable, Credit Quality Indicator [Line Items]
Origination Year - 2020	229
Origination Year - 2019	5,398
Origination Year - 2018	7,778
Origination Year - 2017	625
Origination Year - 2016	1,524
Origination Year - Prior	2,777
Revolving	16,707
Revolving to Term	0
Total	35,038
Commercial portfolio segment \| Commercial & industrial \| Grade 6
Financing Receivable, Credit Quality Indicator [Line Items]
Origination Year - 2020	51
Origination Year - 2019	23
Origination Year - 2018	796
Origination Year - 2017	5,698
Origination Year - 2016	1
Origination Year - Prior	35
Revolving	4,136
Revolving to Term	0
Total	10,740
Commercial portfolio segment \| Commercial & industrial \| Grade 7
Financing Receivable, Credit Quality Indicator [Line Items]
Origination Year - 2020	1,732
Origination Year - 2019	1,215
Origination Year - 2018	1,112
Origination Year - 2017	1,382
Origination Year - 2016	545
Origination Year - Prior	6,057
Revolving	3,826
Revolving to Term	0
Total	15,869
Commercial portfolio segment \| Commercial & industrial
Financing Receivable, Credit Quality Indicator [Line Items]
Total	729,264	806,189
Commercial portfolio segment \| Commercial & industrial \| Grades 1- 4
Financing Receivable, Credit Quality Indicator [Line Items]
Total	667,617	765,073
Commercial portfolio segment \| Commercial & industrial \| Grade 5
Financing Receivable, Credit Quality Indicator [Line Items]
Total	35,038	20,199
Commercial portfolio segment \| Commercial & industrial \| Grade 6
Financing Receivable, Credit Quality Indicator [Line Items]
Total	10,740	7,663
Commercial portfolio segment \| Commercial & industrial \| Grade 7
Financing Receivable, Credit Quality Indicator [Line Items]
Total	15,869	13,254
Commercial portfolio segment \| Owner-occupied commercial real estate (“CRE”)
Financing Receivable, Credit Quality Indicator [Line Items]
Origination Year - 2020	36,065
Origination Year - 2019	68,336
Origination Year - 2018	84,287
Origination Year - 2017	73,477
Origination Year - 2016	51,215
Origination Year - Prior	180,355
Revolving	1,987
Revolving to Term	0
Total	495,722	496,372
Commercial portfolio segment \| Owner-occupied commercial real estate (“CRE”) \| Grades 1- 4
Financing Receivable, Credit Quality Indicator [Line Items]
Origination Year - 2020	36,065
Origination Year - 2019	67,425
Origination Year - 2018	82,360
Origination Year - 2017	62,980
Origination Year - 2016	49,060
Origination Year - Prior	164,982
Revolving	1,499
Revolving to Term	0
Total	464,371	464,661
Commercial portfolio segment \| Owner-occupied commercial real estate (“CRE”) \| Grade 5
Financing Receivable, Credit Quality Indicator [Line Items]
Origination Year - 2020	0
Origination Year - 2019	574
Origination Year - 2018	1,646
Origination Year - 2017	6,572
Origination Year - 2016	379
Origination Year - Prior	7,086
Revolving	488
Revolving to Term	0
Total	16,745	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	1,736
Origination Year - 2016	0
Origination Year - Prior	734
Revolving	0
Revolving to Term	0
Total	2,470	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	337
Origination Year - 2018	281
Origination Year - 2017	2,189
Origination Year - 2016	1,776
Origination Year - Prior	7,553
Revolving	0
Revolving to Term	0
Total	12,136	9,903
Commercial portfolio segment \| Agricultural
Financing Receivable, Credit Quality Indicator [Line Items]
Origination Year - 2020	8,786
Origination Year - 2019	5,859
Origination Year - 2018	7,336
Origination Year - 2017	10,713
Origination Year - 2016	4,521
Origination Year - Prior	40,318
Revolving	21,487
Revolving to Term	0
Total	99,020	95,450
Commercial portfolio segment \| Agricultural \| Grades 1- 4
Financing Receivable, Credit Quality Indicator [Line Items]
Origination Year - 2020	8,766
Origination Year - 2019	5,484
Origination Year - 2018	7,266
Origination Year - 2017	9,697
Origination Year - 2016	2,240
Origination Year - Prior	29,722
Revolving	20,775
Revolving to Term	0
Total	83,950	77,082
Commercial portfolio segment \| Agricultural \| Grade 5
Financing Receivable, Credit Quality Indicator [Line Items]
Origination Year - 2020	20
Origination Year - 2019	375
Origination Year - 2018	36
Origination Year - 2017	573
Origination Year - 2016	689
Origination Year - Prior	4,772
Revolving	633
Revolving to Term	0
Total	7,098	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	34
Origination Year - 2017	115
Origination Year - 2016	1,200
Origination Year - Prior	5,824
Revolving	79
Revolving to Term	0
Total	7,252	8,308
Commercial portfolio segment \| PPP loans
Financing Receivable, Credit Quality Indicator [Line Items]
Total	329,157	0
Commercial portfolio segment \| PPP loans \| Grades 1- 4
Financing Receivable, Credit Quality Indicator [Line Items]
Total	329,157
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	42,819
Origination Year - 2019	76,792
Origination Year - 2018	41,687
Origination Year - 2017	71,399
Origination Year - 2016	41,052
Origination Year - Prior	167,803
Revolving	6,348
Revolving to Term	0
Total	447,900	443,218
Commercial real estate portfolio segment \| CRE investment \| Grades 1- 4
Financing Receivable, Credit Quality Indicator [Line Items]
Origination Year - 2020	42,819
Origination Year - 2019	76,688
Origination Year - 2018	41,581
Origination Year - 2017	69,179
Origination Year - 2016	39,866
Origination Year - Prior	158,663
Revolving	6,303
Revolving to Term	0
Total	435,099	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	106
Origination Year - 2017	1,307
Origination Year - 2016	388
Origination Year - Prior	6,396
Revolving	45
Revolving to Term	0
Total	8,242	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	913
Origination Year - 2016	654
Origination Year - Prior	0
Revolving	0
Revolving to Term	0
Total	1,671	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	144
Origination Year - Prior	2,744
Revolving	0
Revolving to Term	0
Total	2,888	1,761
Commercial real estate portfolio segment \| Construction & land development
Financing Receivable, Credit Quality Indicator [Line Items]
Origination Year - 2020	25,720
Origination Year - 2019	41,766
Origination Year - 2018	22,029
Origination Year - 2017	3,487
Origination Year - 2016	2,261
Origination Year - Prior	10,215
Revolving	1,799
Revolving to Term	0
Total	107,277	92,970
Commercial real estate portfolio segment \| Construction & land development \| Grades 1- 4
Financing Receivable, Credit Quality Indicator [Line Items]
Origination Year - 2020	25,720
Origination Year - 2019	40,447
Origination Year - 2018	19,330
Origination Year - 2017	3,442
Origination Year - 2016	2,261
Origination Year - Prior	9,282
Revolving	1,799
Revolving to Term	0
Total	102,281	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	219
Origination Year - 2018	2,699
Origination Year - 2017	45
Origination Year - 2016	0
Origination Year - Prior	26
Revolving	0
Revolving to Term	0
Total	2,989	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	1,100
Origination Year - 2018	0
Origination Year - 2017	0
Origination Year - 2016	0
Origination Year - Prior	0
Revolving	0
Revolving to Term	0
Total	1,100	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	907
Revolving	0
Revolving to Term	0
Total	907	219
Residential \| Residential construction
Financing Receivable, Credit Quality Indicator [Line Items]
Origination Year - 2020	14,455
Origination Year - 2019	34,859
Origination Year - 2018	1,459
Origination Year - 2017	407
Origination Year - 2016	19
Origination Year - Prior	133
Revolving	0
Revolving to Term	0
Total	51,332	54,403
Residential \| Residential construction \| Grades 1- 4
Financing Receivable, Credit Quality Indicator [Line Items]
Origination Year - 2020	14,455
Origination Year - 2019	34,545
Origination Year - 2018	1,459
Origination Year - 2017	351
Origination Year - 2016	19
Origination Year - Prior	133
Revolving	0
Revolving to Term	0
Total	50,962	53,286
Residential \| Residential construction \| Grade 5
Financing Receivable, Credit Quality Indicator [Line Items]
Origination Year - 2020	0
Origination Year - 2019	314
Origination Year - 2018	0
Origination Year - 2017	56
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	54,206
Origination Year - 2019	73,144
Origination Year - 2018	51,025
Origination Year - 2017	53,403
Origination Year - 2016	53,413
Origination Year - Prior	131,584
Revolving	919
Revolving to Term	0
Total	417,694	432,167
Residential \| Residential first mortgage \| Grades 1- 4
Financing Receivable, Credit Quality Indicator [Line Items]
Origination Year - 2020	54,206
Origination Year - 2019	71,663
Origination Year - 2018	49,497
Origination Year - 2017	53,126
Origination Year - 2016	52,588
Origination Year - Prior	128,667
Revolving	919
Revolving to Term	0
Total	410,666	424,044
Residential \| Residential first mortgage \| Grade 5
Financing Receivable, Credit Quality Indicator [Line Items]
Origination Year - 2020	0
Origination Year - 2019	825
Origination Year - 2018	1,331
Origination Year - 2017	258
Origination Year - 2016	760
Origination Year - Prior	1,689
Revolving	0
Revolving to Term	0
Total	4,863	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	0
Origination Year - 2017	0
Origination Year - 2016	0
Origination Year - Prior	0
Revolving	0
Revolving to Term	0
Total	0	668
Residential \| Residential first mortgage \| Grade 7
Financing Receivable, Credit Quality Indicator [Line Items]
Origination Year - 2020	0
Origination Year - 2019	656
Origination Year - 2018	197
Origination Year - 2017	19
Origination Year - 2016	65
Origination Year - Prior	1,228
Revolving	0
Revolving to Term	0
Total	2,165	2,778
Residential \| Residential junior mortgage
Financing Receivable, Credit Quality Indicator [Line Items]
Origination Year - 2020	2,470

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

Jun. 30, 2020

Dec. 31, 2019

Financing Receivable, Credit Quality Indicator [Line Items]

Origination Year - 2020

$ 589,200

Origination Year - 2019

469,044

Origination Year - 2018

334,235

Origination Year - 2017

292,819