Loans and Allowance for Credit Losses - Loans by Credit Risk Rating, Segregated by Class of Loans (Details) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020
Financing Receivable, Credit Quality Indicator [Line Items]
Total	$ 11,386,352	$ 12,900,897
Loans other than pass or current
Financing Receivable, Credit Quality Indicator [Line Items]
2021 (YTD)	61,384	206,034
2020	118,739	25,804
2019	15,111	43,589
2018	31,537	44,544
2017	80,056	34,311
2016 and Prior	64,418	32,434
Lines of Credit (“LOC”) Amortized Cost Basis	222,021	214,137
LOC Converted to Term Loans Amortized Cost Basis	60,010	93,154
Total	653,276	694,007
Consumer
Financing Receivable, Credit Quality Indicator [Line Items]
Total	359,346	391,224
Consumer | Credit cards
Financing Receivable, Credit Quality Indicator [Line Items]
Total	177,634	188,845
Consumer | Other consumer
Financing Receivable, Credit Quality Indicator [Line Items]
Total	181,712	202,379
Real Estate
Financing Receivable, Credit Quality Indicator [Line Items]
Total	8,368,848	9,223,791
Real Estate | Construction and development
Financing Receivable, Credit Quality Indicator [Line Items]
Total	1,428,165	1,596,255
Real Estate | Construction and development | Special mention
Financing Receivable, Credit Quality Indicator [Line Items]
2021 (YTD)	0	2,728
2020	0	344
2019	292	259
2018	0	2,107
2017	1,360	19
2016 and Prior	0	0
Lines of Credit (“LOC”) Amortized Cost Basis	0	9,613
LOC Converted to Term Loans Amortized Cost Basis	0	0
Total	1,652	15,070
Real Estate | Construction and development | Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
2021 (YTD)	1,740	294
2020	42	2,069
2019	547	404
2018	401	449
2017	333	342
2016 and Prior	733	320
Lines of Credit (“LOC”) Amortized Cost Basis	10,513	17,914
LOC Converted to Term Loans Amortized Cost Basis	1,954	14
Total	16,263	21,806
Real Estate | Construction and development | Doubtful and loss
Financing Receivable, Credit Quality Indicator [Line Items]
2021 (YTD)	0	0
2020	0	0
2019	0	0
2018	0	0
2017	0	0
2016 and Prior	0	0
Lines of Credit (“LOC”) Amortized Cost Basis	0	0
LOC Converted to Term Loans Amortized Cost Basis	0	0
Total	0	0
Real Estate | Construction and development | Risk rate 5, 6, and 7
Financing Receivable, Credit Quality Indicator [Line Items]
2021 (YTD)	1,740	3,022
2020	42	2,413
2019	839	663
2018	401	2,556
2017	1,693	361
2016 and Prior	733	320
Lines of Credit (“LOC”) Amortized Cost Basis	10,513	27,527
LOC Converted to Term Loans Amortized Cost Basis	1,954	14
Total	17,915	36,876
Real Estate | Single family residential
Financing Receivable, Credit Quality Indicator [Line Items]
Total	1,608,028	1,880,673
Real Estate | Other commercial
Financing Receivable, Credit Quality Indicator [Line Items]
Total	5,332,655	5,746,863
Real Estate | Other commercial | Special mention
Financing Receivable, Credit Quality Indicator [Line Items]
2021 (YTD)	30,225	100,085
2020	69,187	4,346
2019	1,818	10,738
2018	8,584	19,943
2017	40,531	26,245
2016 and Prior	34,225	10,608
Lines of Credit (“LOC”) Amortized Cost Basis	127,273	63,305
LOC Converted to Term Loans Amortized Cost Basis	18,393	23,435
Total	330,236	258,705
Real Estate | Other commercial | Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
2021 (YTD)	25,532	66,737
2020	25,865	9,418
2019	6,477	24,380
2018	15,304	14,067
2017	33,640	3,744
2016 and Prior	23,723	11,158
Lines of Credit (“LOC”) Amortized Cost Basis	50,734	52,182
LOC Converted to Term Loans Amortized Cost Basis	20,480	39,486
Total	201,755	221,172
Real Estate | Other commercial | Doubtful and loss
Financing Receivable, Credit Quality Indicator [Line Items]
2021 (YTD)	0	0
2020	0	0
2019	0	0
2018	0	0
2017	0	0
2016 and Prior	0	0
Lines of Credit (“LOC”) Amortized Cost Basis	0	0
LOC Converted to Term Loans Amortized Cost Basis	0	0
Total	0	0
Real Estate | Other commercial | Risk rate 5, 6, and 7
Financing Receivable, Credit Quality Indicator [Line Items]
2021 (YTD)	55,757	166,822
2020	95,052	13,764
2019	8,295	35,118
2018	23,888	34,010
2017	74,171	29,989
2016 and Prior	57,948	21,766
Lines of Credit (“LOC”) Amortized Cost Basis	178,007	115,487
LOC Converted to Term Loans Amortized Cost Basis	38,873	62,921
Total	531,991	479,877
Commercial
Financing Receivable, Credit Quality Indicator [Line Items]
Total	2,268,191	2,750,291
Commercial | Commercial
Financing Receivable, Credit Quality Indicator [Line Items]
Total	2,074,729	2,574,386
Commercial | Commercial | Special mention
Financing Receivable, Credit Quality Indicator [Line Items]
2021 (YTD)	0	5,707
2020	1,247	342
2019	354	465
2018	523	972
2017	392	54
2016 and Prior	752	0
Lines of Credit (“LOC”) Amortized Cost Basis	5,380	12,318
LOC Converted to Term Loans Amortized Cost Basis	12,438	22,546
Total	21,086	42,404
Commercial | Commercial | Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
2021 (YTD)	3,627	23,227
2020	21,024	4,495
2019	3,616	1,586
2018	2,035	730
2017	796	276
2016 and Prior	799	334
Lines of Credit (“LOC”) Amortized Cost Basis	25,859	53,682
LOC Converted to Term Loans Amortized Cost Basis	6,601	7,522
Total	64,357	91,852
Commercial | Commercial | Doubtful and loss
Financing Receivable, Credit Quality Indicator [Line Items]
2021 (YTD)	0	0
2020	0	0
2019	0	0
2018	0	0
2017	0	0
2016 and Prior	0	0
Lines of Credit (“LOC”) Amortized Cost Basis	0	0
LOC Converted to Term Loans Amortized Cost Basis	0	0
Total	0	0
Commercial | Commercial | Risk rate 5, 6, and 7
Financing Receivable, Credit Quality Indicator [Line Items]
2021 (YTD)	3,627	28,934
2020	22,271	4,837
2019	3,970	2,051
2018	2,558	1,702
2017	1,188	330
2016 and Prior	1,551	334
Lines of Credit (“LOC”) Amortized Cost Basis	31,239	66,000
LOC Converted to Term Loans Amortized Cost Basis	19,039	30,068
Total	85,443	134,256
Commercial | Agricultural
Financing Receivable, Credit Quality Indicator [Line Items]
Total	193,462	175,905
Commercial | Agricultural | Special mention
Financing Receivable, Credit Quality Indicator [Line Items]
2021 (YTD)	0	0
2020	0	79
2019	6	13
2018	10	299
2017	15	0
2016 and Prior	0	6
Lines of Credit (“LOC”) Amortized Cost Basis	0	34
LOC Converted to Term Loans Amortized Cost Basis	0	0
Total	31	431
Commercial | Agricultural | Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
2021 (YTD)	105	86
2020	65	101
2019	121	64
2018	294	47
2017	64	12
2016 and Prior	20	10
Lines of Credit (“LOC”) Amortized Cost Basis	229	68
LOC Converted to Term Loans Amortized Cost Basis	72	75
Total	970	463
Commercial | Agricultural | Doubtful and loss
Financing Receivable, Credit Quality Indicator [Line Items]
2021 (YTD)	0	0
2020	0	0
2019	0	0
2018	0	0
2017	0	0
2016 and Prior	0	0
Lines of Credit (“LOC”) Amortized Cost Basis	0	0
LOC Converted to Term Loans Amortized Cost Basis	0	0
Total	0	0
Commercial | Agricultural | Risk rate 5, 6, and 7
Financing Receivable, Credit Quality Indicator [Line Items]
2021 (YTD)	105	86
2020	65	180
2019	127	77
2018	304	346
2017	79	12
2016 and Prior	20	16
Lines of Credit (“LOC”) Amortized Cost Basis	229	102
LOC Converted to Term Loans Amortized Cost Basis	72	75
Total	1,001	894
Other
Financing Receivable, Credit Quality Indicator [Line Items]
Total	389,967	535,591
30-89 days past due | Consumer | Credit cards
Financing Receivable, Credit Quality Indicator [Line Items]
2021 (YTD)	0	0
2020	0	0
2019	0	0
2018	0	0
2017	0	0
2016 and Prior	0	0
Lines of Credit (“LOC”) Amortized Cost Basis	644	708
LOC Converted to Term Loans Amortized Cost Basis	0	0
Total	644	708
30-89 days past due | Consumer | Other consumer
Financing Receivable, Credit Quality Indicator [Line Items]
2021 (YTD)	44	234
2020	193	441
2019	81	327
2018	174	658
2017	178	689
2016 and Prior	208	84
Lines of Credit (“LOC”) Amortized Cost Basis	66	339
LOC Converted to Term Loans Amortized Cost Basis	0	0
Total	944	2,772
30-89 days past due | Real Estate | Single family residential
Financing Receivable, Credit Quality Indicator [Line Items]
2021 (YTD)	111	6,300
2020	1,034	2,258
2019	540	2,593
2018	2,033	2,610
2017	844	2,058
2016 and Prior	1,744	6,050
Lines of Credit (“LOC”) Amortized Cost Basis	505	1,782
LOC Converted to Term Loans Amortized Cost Basis	72	76
Total	6,883	23,727
30-89 days past due | Other
Financing Receivable, Credit Quality Indicator [Line Items]
2021 (YTD)	0
2020	0
2019	0
2018	0
2017	0
2016 and Prior	0
Lines of Credit (“LOC”) Amortized Cost Basis	0
LOC Converted to Term Loans Amortized Cost Basis	0
Total	0
90 Days or More Past Due
Financing Receivable, Credit Quality Indicator [Line Items]
Total	34,812	35,188
90 Days or More Past Due | Consumer
Financing Receivable, Credit Quality Indicator [Line Items]
Total	394	558
90 Days or More Past Due | Consumer | Credit cards
Financing Receivable, Credit Quality Indicator [Line Items]
2021 (YTD)	0	0
2020	0	0
2019	0	0
2018	0	0
2017	0	0
2016 and Prior	0	0
Lines of Credit (“LOC”) Amortized Cost Basis	273	256
LOC Converted to Term Loans Amortized Cost Basis	0	0
Total	273	256
90 Days or More Past Due | Consumer | Other consumer
Financing Receivable, Credit Quality Indicator [Line Items]
2021 (YTD)	0	79
2020	13	58
2019	56	25
2018	2	80
2017	33	40
2016 and Prior	17	12
Lines of Credit (“LOC”) Amortized Cost Basis	0	8
LOC Converted to Term Loans Amortized Cost Basis	0	0
Total	121	302
90 Days or More Past Due | Real Estate
Financing Receivable, Credit Quality Indicator [Line Items]
Total	24,898	27,014
90 Days or More Past Due | Real Estate | Construction and development
Financing Receivable, Credit Quality Indicator [Line Items]
Total	1,595	3,089
90 Days or More Past Due | Real Estate | Single family residential
Financing Receivable, Credit Quality Indicator [Line Items]
2021 (YTD)	0	557
2020	69	1,853
2019	1,203	2,735
2018	2,177	2,582
2017	1,870	832
2016 and Prior	2,197	3,852
Lines of Credit (“LOC”) Amortized Cost Basis	545	1,928
LOC Converted to Term Loans Amortized Cost Basis	0	0
Total	8,061	14,339
90 Days or More Past Due | Real Estate | Other commercial
Financing Receivable, Credit Quality Indicator [Line Items]
Total	15,242	9,586
90 Days or More Past Due | Commercial
Financing Receivable, Credit Quality Indicator [Line Items]
Total	9,520	7,616
90 Days or More Past Due | Commercial | Commercial
Financing Receivable, Credit Quality Indicator [Line Items]
Total	9,167	7,429
90 Days or More Past Due | Commercial | Agricultural
Financing Receivable, Credit Quality Indicator [Line Items]
Total	353	187
90 Days or More Past Due | Other
Financing Receivable, Credit Quality Indicator [Line Items]
2021 (YTD)	0
2020	0
2019	0
2018	0
2017	0
2016 and Prior	0
Lines of Credit (“LOC”) Amortized Cost Basis	0
LOC Converted to Term Loans Amortized Cost Basis	0
Total	0	0
30 + days past due | Consumer | Credit cards
Financing Receivable, Credit Quality Indicator [Line Items]
2021 (YTD)	0	0
2020	0	0
2019	0	0
2018	0	0
2017	0	0
2016 and Prior	0	0
Lines of Credit (“LOC”) Amortized Cost Basis	917	964
LOC Converted to Term Loans Amortized Cost Basis	0	0
Total	917	964
30 + days past due | Consumer | Other consumer
Financing Receivable, Credit Quality Indicator [Line Items]
2021 (YTD)	44	313
2020	206	499
2019	137	352
2018	176	738
2017	211	729
2016 and Prior	225	96
Lines of Credit (“LOC”) Amortized Cost Basis	66	347
LOC Converted to Term Loans Amortized Cost Basis	0	0
Total	1,065	3,074
30 + days past due | Real Estate | Single family residential
Financing Receivable, Credit Quality Indicator [Line Items]
2021 (YTD)	111	6,857
2020	1,103	4,111
2019	1,743	5,328
2018	4,210	5,192
2017	2,714	2,890
2016 and Prior	3,941	9,902
Lines of Credit (“LOC”) Amortized Cost Basis	1,050	3,710
LOC Converted to Term Loans Amortized Cost Basis	72	76
Total	14,944	$ 38,066
30 + days past due | Other
Financing Receivable, Credit Quality Indicator [Line Items]
2021 (YTD)	0
2020	0
2019	0
2018	0
2017	0
2016 and Prior	0
Lines of Credit (“LOC”) Amortized Cost Basis	0
LOC Converted to Term Loans Amortized Cost Basis	0
Total	$ 0