Loans, Allowance for Credit Losses - Loans, and Credit Quality - Summary of loans by loan risk categories (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Financing Receivable, Credit Quality Indicator [Line Items]
Origination Year - 2020	$ 139,886
Origination Year - 2019	492,152
Origination Year - 2018	362,840
Origination Year - 2017	304,129
Origination Year - 2016	206,190
Origination Year - Prior	641,639
Revolving	456,615
Revolving to Term	3,973
Total	$ 2,607,424	$ 2,573,751
Percent of total	100.00%	100.00%
Grades 1- 4
Financing Receivable, Credit Quality Indicator [Line Items]
Total	$ 2,487,144	$ 2,457,922
Percent of total	95.40%	95.50%
Grade 5
Financing Receivable, Credit Quality Indicator [Line Items]
Total	$ 60,858	$ 63,966
Percent of total	2.30%	2.50%
Grade 6
Financing Receivable, Credit Quality Indicator [Line Items]
Total	$ 10,087	$ 15,152
Percent of total	0.40%	0.60%
Grade 7
Financing Receivable, Credit Quality Indicator [Line Items]
Total	$ 49,335	$ 36,711
Percent of total	1.90%	1.40%
Retail & other
Financing Receivable, Credit Quality Indicator [Line Items]
Origination Year - 2020	$ 2,438
Origination Year - 2019	5,605
Origination Year - 2018	2,658
Origination Year - 2017	1,161
Origination Year - 2016	827
Origination Year - Prior	1,156
Revolving	15,637
Revolving to Term	0
Total	29,482	$ 30,211
Retail & other | Grades 1- 4
Financing Receivable, Credit Quality Indicator [Line Items]
Origination Year - 2020	2,438
Origination Year - 2019	5,605
Origination Year - 2018	2,658
Origination Year - 2017	1,161
Origination Year - 2016	827
Origination Year - Prior	1,156
Revolving	15,637
Revolving to Term	0
Total	29,482	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	45,750
Origination Year - 2019	156,650
Origination Year - 2018	127,555
Origination Year - 2017	79,674
Origination Year - 2016	34,579
Origination Year - Prior	74,878
Revolving	312,171
Revolving to Term	0
Total	831,257	806,189
Commercial portfolio segment | Commercial & industrial | Grades 1- 4
Financing Receivable, Credit Quality Indicator [Line Items]
Origination Year - 2020	45,598
Origination Year - 2019	151,079
Origination Year - 2018	118,171
Origination Year - 2017	77,690
Origination Year - 2016	31,727
Origination Year - Prior	64,618
Revolving	291,990
Revolving to Term	0
Total	780,873	765,073
Commercial portfolio segment | Commercial & industrial | Grade 5
Financing Receivable, Credit Quality Indicator [Line Items]
Origination Year - 2020	39
Origination Year - 2019	3,470
Origination Year - 2018	7,446
Origination Year - 2017	576
Origination Year - 2016	1,479
Origination Year - Prior	2,830
Revolving	7,845
Revolving to Term	0
Total	23,685	20,199
Commercial portfolio segment | Commercial & industrial | Grade 6
Financing Receivable, Credit Quality Indicator [Line Items]
Origination Year - 2020	0
Origination Year - 2019	23
Origination Year - 2018	823
Origination Year - 2017	4
Origination Year - 2016	1
Origination Year - Prior	37
Revolving	4,946
Revolving to Term	0
Total	5,834	7,663
Commercial portfolio segment | Commercial & industrial | Grade 7
Financing Receivable, Credit Quality Indicator [Line Items]
Origination Year - 2020	113
Origination Year - 2019	2,078
Origination Year - 2018	1,115
Origination Year - 2017	1,404
Origination Year - 2016	1,372
Origination Year - Prior	7,393
Revolving	7,390
Revolving to Term	0
Total	20,865	13,254
Commercial portfolio segment | Owner-occupied CRE
Financing Receivable, Credit Quality Indicator [Line Items]
Origination Year - 2020	21,337
Origination Year - 2019	69,269
Origination Year - 2018	86,972
Origination Year - 2017	76,342
Origination Year - 2016	52,595
Origination Year - Prior	190,362
Revolving	2,828
Revolving to Term	0
Total	499,705	496,372
Commercial portfolio segment | Owner-occupied CRE | Grades 1- 4
Financing Receivable, Credit Quality Indicator [Line Items]
Origination Year - 2020	21,337
Origination Year - 2019	68,525
Origination Year - 2018	84,981
Origination Year - 2017	64,514
Origination Year - 2016	50,402
Origination Year - Prior	175,204
Revolving	2,340
Revolving to Term	0
Total	467,303	464,661
Commercial portfolio segment | Owner-occupied CRE | Grade 5
Financing Receivable, Credit Quality Indicator [Line Items]
Origination Year - 2020	0
Origination Year - 2019	576
Origination Year - 2018	1,706
Origination Year - 2017	7,882
Origination Year - 2016	396
Origination Year - Prior	6,676
Revolving	488
Revolving to Term	0
Total	17,724	20,855
Commercial portfolio segment | Owner-occupied 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	1,749
Origination Year - 2016	0
Origination Year - Prior	56
Revolving	0
Revolving to Term	0
Total	1,805	953
Commercial portfolio segment | Owner-occupied CRE | Grade 7
Financing Receivable, Credit Quality Indicator [Line Items]
Origination Year - 2020	0
Origination Year - 2019	168
Origination Year - 2018	285
Origination Year - 2017	2,197
Origination Year - 2016	1,797
Origination Year - Prior	8,426
Revolving	0
Revolving to Term	0
Total	12,873	9,903
Commercial portfolio segment | Agricultural
Financing Receivable, Credit Quality Indicator [Line Items]
Origination Year - 2020	4,321
Origination Year - 2019	7,982
Origination Year - 2018	7,700
Origination Year - 2017	11,418
Origination Year - 2016	6,475
Origination Year - Prior	36,678
Revolving	21,417
Revolving to Term	0
Total	95,991	95,450
Commercial portfolio segment | Agricultural | Grades 1- 4
Financing Receivable, Credit Quality Indicator [Line Items]
Origination Year - 2020	4,321
Origination Year - 2019	7,982
Origination Year - 2018	7,604
Origination Year - 2017	10,793
Origination Year - 2016	3,998
Origination Year - Prior	26,721
Revolving	20,468
Revolving to Term	0
Total	81,887	77,082
Commercial portfolio segment | Agricultural | Grade 5
Financing Receivable, Credit Quality Indicator [Line Items]
Origination Year - 2020	0
Origination Year - 2019	0
Origination Year - 2018	38
Origination Year - 2017	179
Origination Year - 2016	710
Origination Year - Prior	4,064
Revolving	89
Revolving to Term	0
Total	5,080	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	329
Origination Year - 2016	392
Origination Year - Prior	0
Revolving	49
Revolving to Term	0
Total	770	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	58
Origination Year - 2017	117
Origination Year - 2016	1,375
Origination Year - Prior	5,893
Revolving	811
Revolving to Term	0
Total	8,254	8,308
Commercial real estate portfolio segment | CRE investment
Financing Receivable, Credit Quality Indicator [Line Items]
Origination Year - 2020	29,442
Origination Year - 2019	72,706
Origination Year - 2018	45,072
Origination Year - 2017	72,285
Origination Year - 2016	45,409
Origination Year - Prior	177,606
Revolving	6,238
Revolving to Term	0
Total	448,758	443,218
Commercial real estate portfolio segment | CRE investment | Grades 1- 4
Financing Receivable, Credit Quality Indicator [Line Items]
Origination Year - 2020	29,442
Origination Year - 2019	72,601
Origination Year - 2018	45,017
Origination Year - 2017	71,370
Origination Year - 2016	44,213
Origination Year - Prior	168,170
Revolving	6,238
Revolving to Term	0
Total	437,051	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	55
Origination Year - 2017	0
Origination Year - 2016	394
Origination Year - Prior	6,629
Revolving	0
Revolving to Term	0
Total	7,078	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	105
Origination Year - 2018	0
Origination Year - 2017	915
Origination Year - 2016	656
Origination Year - Prior	0
Revolving	0
Revolving to Term	0
Total	1,676	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	146
Origination Year - Prior	2,807
Revolving	0
Revolving to Term	0
Total	2,953	1,761
Commercial real estate portfolio segment | Construction & land development
Financing Receivable, Credit Quality Indicator [Line Items]
Origination Year - 2020	7,276
Origination Year - 2019	47,011
Origination Year - 2018	22,875
Origination Year - 2017	3,764
Origination Year - 2016	2,683
Origination Year - Prior	10,768
Revolving	1,678
Revolving to Term	0
Total	96,055	92,970
Commercial real estate portfolio segment | Construction & land development | Grades 1- 4
Financing Receivable, Credit Quality Indicator [Line Items]
Origination Year - 2020	7,276
Origination Year - 2019	46,643
Origination Year - 2018	20,176
Origination Year - 2017	3,719
Origination Year - 2016	2,683
Origination Year - Prior	9,827
Revolving	1,678
Revolving to Term	0
Total	92,002	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	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	149
Origination Year - 2018	0
Origination Year - 2017	0
Origination Year - 2016	0
Origination Year - Prior	915
Revolving	0
Revolving to Term	0
Total	1,064	219
Residential | Residential first mortgage
Financing Receivable, Credit Quality Indicator [Line Items]
Origination Year - 2020	24,900
Origination Year - 2019	81,070
Origination Year - 2018	60,145
Origination Year - 2017	57,077
Origination Year - 2016	61,572
Origination Year - Prior	145,823
Revolving	1,538
Revolving to Term	1
Total	432,126	432,167
Residential | Residential first mortgage | Grades 1- 4
Financing Receivable, Credit Quality Indicator [Line Items]
Origination Year - 2020	24,900
Origination Year - 2019	79,077
Origination Year - 2018	59,651
Origination Year - 2017	56,748
Origination Year - 2016	60,809
Origination Year - Prior	142,975
Revolving	1,538
Revolving to Term	1
Total	425,699	424,044
Residential | Residential first mortgage | Grade 5
Financing Receivable, Credit Quality Indicator [Line Items]
Origination Year - 2020	0
Origination Year - 2019	1,215
Origination Year - 2018	296
Origination Year - 2017	309
Origination Year - 2016	697
Origination Year - Prior	1,153
Revolving	0
Revolving to Term	0
Total	3,670	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	2
Revolving	0
Revolving to Term	0
Total	2	668
Residential | Residential first mortgage | Grade 7
Financing Receivable, Credit Quality Indicator [Line Items]
Origination Year - 2020	0
Origination Year - 2019	778
Origination Year - 2018	198
Origination Year - 2017	20
Origination Year - 2016	66
Origination Year - Prior	1,693
Revolving	0
Revolving to Term	0
Total	2,755	2,778
Residential | Residential junior mortgage
Financing Receivable, Credit Quality Indicator [Line Items]
Origination Year - 2020	927
Origination Year - 2019	7,017
Origination Year - 2018	5,941
Origination Year - 2017	1,886
Origination Year - 2016	2,021
Origination Year - Prior	4,233
Revolving	95,108
Revolving to Term	3,972
Total	121,105	122,771
Residential | Residential junior mortgage | Grades 1- 4
Financing Receivable, Credit Quality Indicator [Line Items]
Origination Year - 2020	927
Origination Year - 2019	7,017
Origination Year - 2018	5,941
Origination Year - 2017	1,856
Origination Year - 2016	2,021
Origination Year - Prior	3,844
Revolving	95,033
Revolving to Term	3,861
Total	120,500	122,249
Residential | Residential junior mortgage | 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	34
Revolving	0
Revolving to Term	0
Total	34	35
Residential | Residential junior 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	0
Residential | Residential junior mortgage | Grade 7
Financing Receivable, Credit Quality Indicator [Line Items]
Origination Year - 2020	0
Origination Year - 2019	0
Origination Year - 2018	0
Origination Year - 2017	30
Origination Year - 2016	0
Origination Year - Prior	355
Revolving	75
Revolving to Term	111
Total	571	487
Residential | Residential construction
Financing Receivable, Credit Quality Indicator [Line Items]
Origination Year - 2020	3,495
Origination Year - 2019	44,842
Origination Year - 2018	3,922
Origination Year - 2017	522
Origination Year - 2016	29
Origination Year - Prior	135
Revolving	0
Revolving to Term	0
Total	52,945	54,403
Residential | Residential construction | Grades 1- 4
Financing Receivable, Credit Quality Indicator [Line Items]
Origination Year - 2020	3,495
Origination Year - 2019	44,300
Origination Year - 2018	3,922
Origination Year - 2017	466
Origination Year - 2016	29
Origination Year - Prior	135
Revolving	0
Revolving to Term	0
Total	52,347	53,286
Residential | Residential construction | Grade 5
Financing Receivable, Credit Quality Indicator [Line Items]
Origination Year - 2020	0
Origination Year - 2019	542
Origination Year - 2018	0
Origination Year - 2017	56
Origination Year - 2016	0
Origination Year - Prior	0
Revolving	0
Revolving to Term	0
Total	598	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