Loans Receivable and the Allowance for Credit Losses - Loans by Credit Quality Indicator (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Financing Receivable, Recorded Investment
2020	$ 1,314,105
2019	520,076
2018	323,639
2017	328,382
2016	219,013
Prior	443,293
Revolving Loans	448,531
Loans, gross	3,597,039	$ 3,451,266
Performing
Financing Receivable, Recorded Investment
2020	88,039
2019	93,071
2018	82,938
2017	62,272
2016	51,517
Prior	99,730
Revolving Loans	123,134
Loans, gross	600,701
Nonperforming
Financing Receivable, Recorded Investment
2020	17
2019	105
2018	637
2017	1,148
2016	1,194
Prior	3,063
Revolving Loans	71
Loans, gross	6,235
Pass
Financing Receivable, Recorded Investment
2020	1,089,802
2019	382,156
2018	217,711
2017	247,987
2016	157,122
Prior	316,755
Revolving Loans	289,119
Loans, gross	2,700,652	3,246,524
Special mention / watch
Financing Receivable, Recorded Investment
2020	103,489
2019	33,508
2018	10,964
2017	12,835
2016	7,372
Prior	10,901
Revolving Loans	25,373
Loans, gross	204,442	121,709
Substandard
Financing Receivable, Recorded Investment
2020	32,758
2019	11,236
2018	11,389
2017	4,140
2016	1,808
Prior	12,844
Revolving Loans	10,834
Loans, gross	85,009	82,813
Doubtful
Financing Receivable, Recorded Investment
2020	0
Loans, gross	0	184
Loss
Financing Receivable, Recorded Investment
Loans, gross		36
Agricultural
Financing Receivable, Recorded Investment
2020	28,011
2019	14,004
2018	5,025
2017	3,210
2016	3,484
Prior	4,547
Revolving Loans	82,556
Loans, gross	140,837	140,446
Agricultural | Pass
Financing Receivable, Recorded Investment
2020	21,013
2019	11,300
2018	4,898
2017	2,906
2016	2,753
Prior	3,067
Revolving Loans	71,689
Loans, gross	117,626	117,374
Agricultural | Special mention / watch
Financing Receivable, Recorded Investment
2020	5,905
2019	1,422
2018	125
2017	113
2016	600
Prior	1,253
Revolving Loans	6,206
Loans, gross	15,624	13,292
Agricultural | Substandard
Financing Receivable, Recorded Investment
2020	1,093
2019	1,282
2018	2
2017	191
2016	131
Prior	227
Revolving Loans	4,661
Loans, gross	7,587	9,780
Agricultural | Doubtful
Financing Receivable, Recorded Investment
2020	0
Loans, gross	0	0
Agricultural | Loss
Financing Receivable, Recorded Investment
Loans, gross		0
Commercial and industrial
Financing Receivable, Recorded Investment
2020	494,683
2019	118,194
2018	72,788
2017	82,376
2016	45,618
Prior	122,207
Revolving Loans	148,661
Loans, gross	1,084,527	835,236
Commercial and industrial | Pass
Financing Receivable, Recorded Investment
2020	486,629
2019	114,316
2018	70,083
2017	77,159
2016	44,088
Prior	114,435
Revolving Loans	125,003
Loans, gross	1,031,713	794,526
Commercial and industrial | Special mention / watch
Financing Receivable, Recorded Investment
2020	5,018
2019	1,309
2018	1,953
2017	4,243
2016	906
Prior	3,356
Revolving Loans	18,615
Loans, gross	35,400	19,038
Commercial and industrial | Substandard
Financing Receivable, Recorded Investment
2020	3,036
2019	2,569
2018	752
2017	974
2016	624
Prior	4,416
Revolving Loans	5,043
Loans, gross	17,414	21,635
Commercial and industrial | Doubtful
Financing Receivable, Recorded Investment
2020	0
Loans, gross	0	1
Commercial and industrial | Loss
Financing Receivable, Recorded Investment
Loans, gross		36
Commercial real estate
Financing Receivable, Recorded Investment
Loans, gross	1,764,739	1,814,859
Commercial real estate | Pass
Financing Receivable, Recorded Investment
Loans, gross		1,687,570
Commercial real estate | Special mention / watch
Financing Receivable, Recorded Investment
Loans, gross		83,511
Commercial real estate | Substandard
Financing Receivable, Recorded Investment
Loans, gross		43,778
Commercial real estate | Doubtful
Financing Receivable, Recorded Investment
Loans, gross		0
Commercial real estate | Loss
Financing Receivable, Recorded Investment
Loans, gross		0
Commercial real estate | Construction & development
Financing Receivable, Recorded Investment
2020	54,942
2019	80,303
2018	26,219
2017	8,655
2016	1,946
Prior	1,391
Revolving Loans	26,494
Loans, gross	199,950	298,077
Commercial real estate | Construction & development | Pass
Financing Receivable, Recorded Investment
2020	50,048
2019	76,696
2018	25,444
2017	8,655
2016	1,932
Prior	1,308
Revolving Loans	26,494
Loans, gross	190,577	283,921
Commercial real estate | Construction & development | Special mention / watch
Financing Receivable, Recorded Investment
2020	4,159
2019	1,688
2018	775
2016	14
Prior	34
Loans, gross	6,670	11,423
Commercial real estate | Construction & development | Substandard
Financing Receivable, Recorded Investment
2020	735
2019	1,919
Prior	49
Loans, gross	2,703	2,733
Commercial real estate | Construction & development | Doubtful
Financing Receivable, Recorded Investment
2020	0
Loans, gross	0	0
Commercial real estate | Construction & development | Loss
Financing Receivable, Recorded Investment
Loans, gross		0
Commercial real estate | Farmland
Financing Receivable, Recorded Investment
2020	42,116
2019	40,443
2018	19,944
2017	18,705
2016	12,276
Prior	24,809
Revolving Loans	3,604
Loans, gross	161,897	181,885
Commercial real estate | Farmland | Pass
Financing Receivable, Recorded Investment
2020	37,140
2019	32,227
2018	14,315
2017	15,023
2016	10,590
Prior	18,171
Revolving Loans	2,257
Loans, gross	129,723	141,107
Commercial real estate | Farmland | Special mention / watch
Financing Receivable, Recorded Investment
2020	2,244
2019	4,584
2018	1,290
2017	1,953
2016	1,237
Prior	587
Revolving Loans	353
Loans, gross	12,248	21,307
Commercial real estate | Farmland | Substandard
Financing Receivable, Recorded Investment
2020	2,732
2019	3,632
2018	4,339
2017	1,729
2016	449
Prior	6,051
Revolving Loans	994
Loans, gross	19,926	19,471
Commercial real estate | Farmland | Doubtful
Financing Receivable, Recorded Investment
2020	0
Loans, gross	0	0
Commercial real estate | Farmland | Loss
Financing Receivable, Recorded Investment
Loans, gross		0
Commercial real estate | Multifamily
Financing Receivable, Recorded Investment
2020	110,701
2019	18,302
2018	18,346
2017	37,740
2016	16,800
Prior	32,726
Revolving Loans	12,788
Loans, gross	247,403	227,407
Commercial real estate | Multifamily | Pass
Financing Receivable, Recorded Investment
2020	109,637
2019	17,948
2018	18,346
2017	37,740
2016	16,722
Prior	32,726
Revolving Loans	12,788
Loans, gross	245,907	226,124
Commercial real estate | Multifamily | Special mention / watch
Financing Receivable, Recorded Investment
2020	348
2016	78
Loans, gross	426	90
Commercial real estate | Multifamily | Substandard
Financing Receivable, Recorded Investment
2020	716
2019	354
Loans, gross	1,070	1,193
Commercial real estate | Multifamily | Doubtful
Financing Receivable, Recorded Investment
2020	0
Loans, gross	0	0
Commercial real estate | Multifamily | Loss
Financing Receivable, Recorded Investment
Loans, gross		0
Commercial real estate | Commercial real estate-other
Financing Receivable, Recorded Investment
2020	495,596
2019	155,654
2018	97,742
2017	114,276
2016	86,178
Prior	154,820
Revolving Loans	51,223
Loans, gross	1,155,489	1,107,490
Commercial real estate | Commercial real estate-other | Pass
Financing Receivable, Recorded Investment
2020	385,335
2019	129,669
2018	84,625
2017	106,504
2016	81,037
Prior	147,048
Revolving Loans	50,888
Loans, gross	985,106	1,036,418
Commercial real estate | Commercial real estate-other | Special mention / watch
Financing Receivable, Recorded Investment
2020	85,815
2019	24,505
2018	6,821
2017	6,526
2016	4,537
Prior	5,671
Revolving Loans	199
Loans, gross	134,074	50,691
Commercial real estate | Commercial real estate-other | Substandard
Financing Receivable, Recorded Investment
2020	24,446
2019	1,480
2018	6,296
2017	1,246
2016	604
Prior	2,101
Revolving Loans	136
Loans, gross	36,309	20,381
Commercial real estate | Commercial real estate-other | Doubtful
Financing Receivable, Recorded Investment
2020	0
Loans, gross	0	0
Commercial real estate | Commercial real estate-other | Loss
Financing Receivable, Recorded Investment
Loans, gross		0
Residential real estate
Financing Receivable, Recorded Investment
Loans, gross	532,914	577,799
Residential real estate | Pass
Financing Receivable, Recorded Investment
Loans, gross		564,404
Residential real estate | Special mention / watch
Financing Receivable, Recorded Investment
Loans, gross		5,829
Residential real estate | Substandard
Financing Receivable, Recorded Investment
Loans, gross		7,402
Residential real estate | Doubtful
Financing Receivable, Recorded Investment
Loans, gross		164
Residential real estate | Loss
Financing Receivable, Recorded Investment
Loans, gross		0
Residential real estate | One- to four- family first liens
Financing Receivable, Recorded Investment
2020	71,436
2019	61,247
2018	52,818
2017	48,300
2016	44,497
Prior	88,756
Revolving Loans	10,046
Loans, gross	377,100	407,418
Residential real estate | One- to four- family first liens | Performing
Financing Receivable, Recorded Investment
2020	71,419
2019	61,180
2018	52,230
2017	47,208
2016	43,567
Prior	85,959
Revolving Loans	10,046
Loans, gross	371,609
Residential real estate | One- to four- family first liens | Nonperforming
Financing Receivable, Recorded Investment
2020	17
2019	67
2018	588
2017	1,092
2016	930
Prior	2,797
Revolving Loans	0
Loans, gross	5,491
Residential real estate | One- to four- family first liens | Pass
Financing Receivable, Recorded Investment
Loans, gross		396,175
Residential real estate | One- to four- family first liens | Special mention / watch
Financing Receivable, Recorded Investment
Loans, gross		4,547
Residential real estate | One- to four- family first liens | Substandard
Financing Receivable, Recorded Investment
Loans, gross		6,532
Residential real estate | One- to four- family first liens | Doubtful
Financing Receivable, Recorded Investment
Loans, gross		164
Residential real estate | One- to four- family first liens | Loss
Financing Receivable, Recorded Investment
Loans, gross		0
Residential real estate | One- to four- family junior liens
Financing Receivable, Recorded Investment
2020	3,687
2019	12,453
2018	16,629
2017	8,239
2016	4,593
Prior	7,797
Revolving Loans	102,416
Loans, gross	155,814	170,381
Residential real estate | One- to four- family junior liens | Performing
Financing Receivable, Recorded Investment
2020	3,687
2019	12,453
2018	16,629
2017	8,207
2016	4,343
Prior	7,568
Revolving Loans	102,345
Loans, gross	155,232
Residential real estate | One- to four- family junior liens | Nonperforming
Financing Receivable, Recorded Investment
2020	0
2019	0
2018	0
2017	32
2016	250
Prior	229
Revolving Loans	71
Loans, gross	582
Residential real estate | One- to four- family junior liens | Pass
Financing Receivable, Recorded Investment
Loans, gross		168,229
Residential real estate | One- to four- family junior liens | Special mention / watch
Financing Receivable, Recorded Investment
Loans, gross		1,282
Residential real estate | One- to four- family junior liens | Substandard
Financing Receivable, Recorded Investment
Loans, gross		870
Residential real estate | One- to four- family junior liens | Doubtful
Financing Receivable, Recorded Investment
Loans, gross		0
Residential real estate | One- to four- family junior liens | Loss
Financing Receivable, Recorded Investment
Loans, gross		0
Consumer
Financing Receivable, Recorded Investment
2020	12,933
2019	19,476
2018	14,128
2017	6,881
2016	3,621
Prior	6,240
Revolving Loans	10,743
Loans, gross	74,022	82,926
Consumer | Performing
Financing Receivable, Recorded Investment
2020	12,933
2019	19,438
2018	14,079
2017	6,857
2016	3,607
Prior	6,203
Revolving Loans	10,743
Loans, gross	73,860
Consumer | Nonperforming
Financing Receivable, Recorded Investment
2020	0
2019	38
2018	49
2017	24
2016	14
Prior	37
Revolving Loans	0
Loans, gross	$ 162
Consumer | Pass
Financing Receivable, Recorded Investment
Loans, gross		82,650
Consumer | Special mention / watch
Financing Receivable, Recorded Investment
Loans, gross		39
Consumer | Substandard
Financing Receivable, Recorded Investment
Loans, gross		218
Consumer | Doubtful
Financing Receivable, Recorded Investment
Loans, gross		19
Consumer | Loss
Financing Receivable, Recorded Investment
Loans, gross		$ 0