Loans and Allowance for Credit Losses - Loans by Credit Risk Rating, Segregated by Class of Loans (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	$ 12,900,897	$ 14,425,704
Total		14,425,704
Risk Rate 1-4
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total		14,113,275
Risk Rate 5
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total		102,618
Risk Rate 6
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total		209,421
Risk Rate 7
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total		173
Risk Rate 8
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total		217
Loans other than pass or current
Accounts, Notes, Loans and Financing Receivable [Line Items]
2020	206,034
2019	25,804
2018	43,589
2017	44,544
2016	34,311
2015 and Prior	32,434
Lines of Credit (“LOC”) Amortized Cost Basis	214,137
LOC Converted to Term Loans Amortized Cost Basis	93,154
Total loans	694,007
Consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	391,224	454,496
Consumer | Loans, Excluding Acquired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total		454,496
Consumer | Risk Rate 1-4 | Loans, Excluding Acquired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total		451,829
Consumer | Risk Rate 5 | Loans, Excluding Acquired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total		0
Consumer | Risk Rate 6 | Loans, Excluding Acquired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total		2,667
Consumer | Risk Rate 7 | Loans, Excluding Acquired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total		0
Consumer | Risk Rate 8 | Loans, Excluding Acquired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total		0
Consumer | Credit cards
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	180,354	204,802
Consumer | Credit cards | Loans, Excluding Acquired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total		204,802
Consumer | Credit cards | Risk Rate 1-4 | Loans, Excluding Acquired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total		204,161
Consumer | Credit cards | Risk Rate 5 | Loans, Excluding Acquired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total		0
Consumer | Credit cards | Risk Rate 6 | Loans, Excluding Acquired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total		641
Consumer | Credit cards | Risk Rate 7 | Loans, Excluding Acquired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total		0
Consumer | Credit cards | Risk Rate 8 | Loans, Excluding Acquired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total		0
Consumer | Other consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	210,870	249,694
Consumer | Other consumer | Loans, Excluding Acquired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total		249,694
Consumer | Other consumer | Risk Rate 1-4 | Loans, Excluding Acquired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total		247,668
Consumer | Other consumer | Risk Rate 5 | Loans, Excluding Acquired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total		0
Consumer | Other consumer | Risk Rate 6 | Loans, Excluding Acquired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total		2,026
Consumer | Other consumer | Risk Rate 7 | Loans, Excluding Acquired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total		0
Consumer | Other consumer | Risk Rate 8 | Loans, Excluding Acquired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total		0
Real Estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	9,223,791	10,884,524
Real Estate | Loans, Excluding Acquired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total		10,884,524
Real Estate | Risk Rate 1-4 | Loans, Excluding Acquired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total		10,691,728
Real Estate | Risk Rate 5 | Loans, Excluding Acquired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total		75,864
Real Estate | Risk Rate 6 | Loans, Excluding Acquired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total		116,765
Real Estate | Risk Rate 7 | Loans, Excluding Acquired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total		130
Real Estate | Risk Rate 8 | Loans, Excluding Acquired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total		37
Real Estate | Construction and development
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	1,596,255	2,236,861
Real Estate | Construction and development | Loans, Excluding Acquired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total		2,236,861
Real Estate | Construction and development | Risk Rate 1-4 | Loans, Excluding Acquired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total		2,229,019
Real Estate | Construction and development | Risk Rate 5
Accounts, Notes, Loans and Financing Receivable [Line Items]
2020	2,728
2019	344
2018	259
2017	2,107
2016	19
2015 and Prior	0
Lines of Credit (“LOC”) Amortized Cost Basis	9,613
LOC Converted to Term Loans Amortized Cost Basis	0
Total loans	15,070
Real Estate | Construction and development | Risk Rate 5 | Loans, Excluding Acquired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total		70
Real Estate | Construction and development | Risk Rate 6
Accounts, Notes, Loans and Financing Receivable [Line Items]
2020	294
2019	2,069
2018	404
2017	449
2016	342
2015 and Prior	320
Lines of Credit (“LOC”) Amortized Cost Basis	17,914
LOC Converted to Term Loans Amortized Cost Basis	14
Total loans	21,806
Real Estate | Construction and development | Risk Rate 6 | Loans, Excluding Acquired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total		7,735
Real Estate | Construction and development | Risk Rate 7
Accounts, Notes, Loans and Financing Receivable [Line Items]
2020	0
2019	0
2018	0
2017	0
2016	0
2015 and Prior	0
Lines of Credit (“LOC”) Amortized Cost Basis	0
LOC Converted to Term Loans Amortized Cost Basis	0
Total loans	0
Real Estate | Construction and development | Risk Rate 7 | Loans, Excluding Acquired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total		0
Real Estate | Construction and development | Risk Rate 8 | Loans, Excluding Acquired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total		37
Real Estate | Construction and development | Risk rate 5, 6, and 7
Accounts, Notes, Loans and Financing Receivable [Line Items]
2020	3,022
2019	2,413
2018	663
2017	2,556
2016	361
2015 and Prior	320
Lines of Credit (“LOC”) Amortized Cost Basis	27,527
LOC Converted to Term Loans Amortized Cost Basis	14
Total loans	36,876
Real Estate | Single family residential
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	1,880,673	2,442,064
Real Estate | Single family residential | Loans, Excluding Acquired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total		2,442,064
Real Estate | Single family residential | Risk Rate 1-4 | Loans, Excluding Acquired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total		2,394,284
Real Estate | Single family residential | Risk Rate 5 | Loans, Excluding Acquired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total		6,049
Real Estate | Single family residential | Risk Rate 6 | Loans, Excluding Acquired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total		41,601
Real Estate | Single family residential | Risk Rate 7 | Loans, Excluding Acquired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total		130
Real Estate | Single family residential | Risk Rate 8 | Loans, Excluding Acquired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total		0
Real Estate | Other commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	5,746,863	6,205,599
Real Estate | Other commercial | Loans, Excluding Acquired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total		6,205,599
Real Estate | Other commercial | Risk Rate 1-4 | Loans, Excluding Acquired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total		6,068,425
Real Estate | Other commercial | Risk Rate 5
Accounts, Notes, Loans and Financing Receivable [Line Items]
2020	100,085
2019	4,346
2018	10,738
2017	19,943
2016	26,245
2015 and Prior	10,608
Lines of Credit (“LOC”) Amortized Cost Basis	63,305
LOC Converted to Term Loans Amortized Cost Basis	23,435
Total loans	258,705
Real Estate | Other commercial | Risk Rate 5 | Loans, Excluding Acquired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total		69,745
Real Estate | Other commercial | Risk Rate 6
Accounts, Notes, Loans and Financing Receivable [Line Items]
2020	66,737
2019	9,418
2018	24,380
2017	14,067
2016	3,744
2015 and Prior	11,158
Lines of Credit (“LOC”) Amortized Cost Basis	52,182
LOC Converted to Term Loans Amortized Cost Basis	39,486
Total loans	221,172
Real Estate | Other commercial | Risk Rate 6 | Loans, Excluding Acquired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total		67,429
Real Estate | Other commercial | Risk Rate 7
Accounts, Notes, Loans and Financing Receivable [Line Items]
2020	0
2019	0
2018	0
2017	0
2016	0
2015 and Prior	0
Lines of Credit (“LOC”) Amortized Cost Basis	0
LOC Converted to Term Loans Amortized Cost Basis	0
Total loans	0
Real Estate | Other commercial | Risk Rate 7 | Loans, Excluding Acquired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total		0
Real Estate | Other commercial | Risk Rate 8 | Loans, Excluding Acquired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total		0
Real Estate | Other commercial | Risk rate 5, 6, and 7
Accounts, Notes, Loans and Financing Receivable [Line Items]
2020	166,822
2019	13,764
2018	35,118
2017	34,010
2016	29,989
2015 and Prior	21,766
Lines of Credit (“LOC”) Amortized Cost Basis	115,487
LOC Converted to Term Loans Amortized Cost Basis	62,921
Total loans	479,877
Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	2,750,291	2,810,970
Commercial | Loans, Excluding Acquired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total		2,810,970
Commercial | Risk Rate 1-4 | Loans, Excluding Acquired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total		2,694,004
Commercial | Risk Rate 5 | Loans, Excluding Acquired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total		26,754
Commercial | Risk Rate 6 | Loans, Excluding Acquired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total		89,989
Commercial | Risk Rate 7 | Loans, Excluding Acquired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total		43
Commercial | Risk Rate 8 | Loans, Excluding Acquired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total		180
Commercial | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	2,574,386	2,495,516
Commercial | Commercial | Loans, Excluding Acquired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total		2,495,516
Commercial | Commercial | Risk Rate 1-4 | Loans, Excluding Acquired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total		2,384,263
Commercial | Commercial | Risk Rate 5
Accounts, Notes, Loans and Financing Receivable [Line Items]
2020	5,707
2019	342
2018	465
2017	972
2016	54
2015 and Prior	0
Lines of Credit (“LOC”) Amortized Cost Basis	12,318
LOC Converted to Term Loans Amortized Cost Basis	22,546
Total loans	42,404
Commercial | Commercial | Risk Rate 5 | Loans, Excluding Acquired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total		26,713
Commercial | Commercial | Risk Rate 6
Accounts, Notes, Loans and Financing Receivable [Line Items]
2020	23,227
2019	4,495
2018	1,586
2017	730
2016	276
2015 and Prior	334
Lines of Credit (“LOC”) Amortized Cost Basis	53,682
LOC Converted to Term Loans Amortized Cost Basis	7,522
Total loans	91,852
Commercial | Commercial | Risk Rate 6 | Loans, Excluding Acquired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total		84,317
Commercial | Commercial | Risk Rate 7
Accounts, Notes, Loans and Financing Receivable [Line Items]
2020	0
2019	0
2018	0
2017	0
2016	0
2015 and Prior	0
Lines of Credit (“LOC”) Amortized Cost Basis	0
LOC Converted to Term Loans Amortized Cost Basis	0
Total loans	0
Commercial | Commercial | Risk Rate 7 | Loans, Excluding Acquired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total		43
Commercial | Commercial | Risk Rate 8 | Loans, Excluding Acquired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total		180
Commercial | Commercial | Risk rate 5, 6, and 7
Accounts, Notes, Loans and Financing Receivable [Line Items]
2020	28,934
2019	4,837
2018	2,051
2017	1,702
2016	330
2015 and Prior	334
Lines of Credit (“LOC”) Amortized Cost Basis	66,000
LOC Converted to Term Loans Amortized Cost Basis	30,068
Total loans	134,256
Commercial | Agricultural
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	175,905	315,454
Commercial | Agricultural | Loans, Excluding Acquired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total		315,454
Commercial | Agricultural | Risk Rate 1-4 | Loans, Excluding Acquired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total		309,741
Commercial | Agricultural | Risk Rate 5
Accounts, Notes, Loans and Financing Receivable [Line Items]
2020	0
2019	79
2018	13
2017	299
2016	0
2015 and Prior	6
Lines of Credit (“LOC”) Amortized Cost Basis	34
LOC Converted to Term Loans Amortized Cost Basis	0
Total loans	431
Commercial | Agricultural | Risk Rate 5 | Loans, Excluding Acquired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total		41
Commercial | Agricultural | Risk Rate 6
Accounts, Notes, Loans and Financing Receivable [Line Items]
2020	86
2019	101
2018	64
2017	47
2016	12
2015 and Prior	10
Lines of Credit (“LOC”) Amortized Cost Basis	68
LOC Converted to Term Loans Amortized Cost Basis	75
Total loans	463
Commercial | Agricultural | Risk Rate 6 | Loans, Excluding Acquired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total		5,672
Commercial | Agricultural | Risk Rate 7
Accounts, Notes, Loans and Financing Receivable [Line Items]
2020	0
2019	0
2018	0
2017	0
2016	0
2015 and Prior	0
Lines of Credit (“LOC”) Amortized Cost Basis	0
LOC Converted to Term Loans Amortized Cost Basis	0
Total loans	0
Commercial | Agricultural | Risk Rate 7 | Loans, Excluding Acquired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total		0
Commercial | Agricultural | Risk Rate 8 | Loans, Excluding Acquired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total		0
Commercial | Agricultural | Risk rate 5, 6, and 7
Accounts, Notes, Loans and Financing Receivable [Line Items]
2020	86
2019	180
2018	77
2017	346
2016	12
2015 and Prior	16
Lines of Credit (“LOC”) Amortized Cost Basis	102
LOC Converted to Term Loans Amortized Cost Basis	75
Total loans	894
Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	535,591	275,714
Other | Loans, Excluding Acquired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total		275,714
Other | Risk Rate 1-4 | Loans, Excluding Acquired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total		275,714
Other | Risk Rate 5 | Loans, Excluding Acquired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total		0
Other | Risk Rate 6 | Loans, Excluding Acquired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total		0
Other | Risk Rate 7 | Loans, Excluding Acquired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total		0
Other | Risk Rate 8 | Loans, Excluding Acquired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total		$ 0
30-89 days past due | Consumer | Credit cards
Accounts, Notes, Loans and Financing Receivable [Line Items]
2020	0
2019	0
2018	0
2017	0
2016	0
2015 and Prior	0
Lines of Credit (“LOC”) Amortized Cost Basis	708
LOC Converted to Term Loans Amortized Cost Basis	0
Total loans	708
30-89 days past due | Consumer | Other consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
2020	234
2019	441
2018	327
2017	658
2016	689
2015 and Prior	84
Lines of Credit (“LOC”) Amortized Cost Basis	339
LOC Converted to Term Loans Amortized Cost Basis	0
Total loans	2,772
30-89 days past due | Real Estate | Single family residential
Accounts, Notes, Loans and Financing Receivable [Line Items]
2020	6,300
2019	2,258
2018	2,593
2017	2,610
2016	2,058
2015 and Prior	6,050
Lines of Credit (“LOC”) Amortized Cost Basis	1,782
LOC Converted to Term Loans Amortized Cost Basis	76
Total loans	23,727
90 Days or More Past Due | Consumer | Credit cards
Accounts, Notes, Loans and Financing Receivable [Line Items]
2020	0
2019	0
2018	0
2017	0
2016	0
2015 and Prior	0
Lines of Credit (“LOC”) Amortized Cost Basis	256
LOC Converted to Term Loans Amortized Cost Basis	0
Total loans	256
90 Days or More Past Due | Consumer | Other consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
2020	79
2019	58
2018	25
2017	80
2016	40
2015 and Prior	12
Lines of Credit (“LOC”) Amortized Cost Basis	8
LOC Converted to Term Loans Amortized Cost Basis	0
Total loans	302
90 Days or More Past Due | Real Estate | Single family residential
Accounts, Notes, Loans and Financing Receivable [Line Items]
2020	557
2019	1,853
2018	2,735
2017	2,582
2016	832
2015 and Prior	3,852
Lines of Credit (“LOC”) Amortized Cost Basis	1,928
LOC Converted to Term Loans Amortized Cost Basis	0
Total loans	14,339
30 + days past due | Consumer | Credit cards
Accounts, Notes, Loans and Financing Receivable [Line Items]
2020	0
2019	0
2018	0
2017	0
2016	0
2015 and Prior	0
Lines of Credit (“LOC”) Amortized Cost Basis	964
LOC Converted to Term Loans Amortized Cost Basis	0
Total loans	964
30 + days past due | Consumer | Other consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
2020	313
2019	499
2018	352
2017	738
2016	729
2015 and Prior	96
Lines of Credit (“LOC”) Amortized Cost Basis	347
LOC Converted to Term Loans Amortized Cost Basis	0
Total loans	3,074
30 + days past due | Real Estate | Single family residential
Accounts, Notes, Loans and Financing Receivable [Line Items]
2020	6,857
2019	4,111
2018	5,328
2017	5,192
2016	2,890
2015 and Prior	9,902
Lines of Credit (“LOC”) Amortized Cost Basis	3,710
LOC Converted to Term Loans Amortized Cost Basis	76
Total loans	$ 38,066