Loans and Allowance for Credit Losses - Loans by Credit Risk Rating, Segregated by Class of Loans (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Financing Receivable, Credit Quality Indicator [Line Items]
Total	$ 10,825,227	$ 12,900,897
Loans other than pass or current
Financing Receivable, Credit Quality Indicator [Line Items]
2021 (YTD)	1,607,033	3,682,340
2020	1,535,869	1,019,712
2019	681,439	922,657
2018	678,561	913,379
2017	794,502	658,250
2016 and Prior	971,256	612,237
Lines of Credit (“LOC”) Amortized Cost Basis	4,213,000	4,725,168
LOC Converted to Term Loans Amortized Cost Basis	343,567	367,154
Total	10,825,227	12,900,897
Consumer
Financing Receivable, Credit Quality Indicator [Line Items]
Total	358,376	391,224
Consumer | Credit cards
Financing Receivable, Credit Quality Indicator [Line Items]
Total	175,884	188,845
Consumer | Other consumer
Financing Receivable, Credit Quality Indicator [Line Items]
Total	182,492	202,379
Real Estate
Financing Receivable, Credit Quality Indicator [Line Items]
Total	8,079,343	9,223,791
Real Estate | Construction and development
Financing Receivable, Credit Quality Indicator [Line Items]
Total	1,229,740	1,596,255
Real Estate | Construction and development | Pass
Financing Receivable, Credit Quality Indicator [Line Items]
2021 (YTD)	47,644	165,990
2020	94,278	35,989
2019	33,487	31,279
2018	19,254	15,960
2017	12,848	9,233
2016 and Prior	10,030	4,807
Lines of Credit (“LOC”) Amortized Cost Basis	982,776	1,272,870
LOC Converted to Term Loans Amortized Cost Basis	21,429	23,251
Total	1,221,746	1,559,379
Real Estate | Construction and development | Special mention
Financing Receivable, Credit Quality Indicator [Line Items]
2021 (YTD)	0	2,728
2020	0	344
2019	279	259
2018	0	2,107
2017	0	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	279	15,070
Real Estate | Construction and development | Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
2021 (YTD)	1,801	294
2020	83	2,069
2019	146	404
2018	57	449
2017	328	342
2016 and Prior	674	320
Lines of Credit (“LOC”) Amortized Cost Basis	2,673	17,914
LOC Converted to Term Loans Amortized Cost Basis	1,953	14
Total	7,715	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)	49,445	169,012
2020	94,361	38,402
2019	33,912	31,942
2018	19,311	18,516
2017	13,176	9,594
2016 and Prior	10,704	5,127
Lines of Credit (“LOC”) Amortized Cost Basis	985,449	1,300,397
LOC Converted to Term Loans Amortized Cost Basis	23,382	23,265
Total	1,229,740	1,596,255
Real Estate | Single family residential
Financing Receivable, Credit Quality Indicator [Line Items]
Total	1,540,701	1,880,673
Real Estate | Other commercial
Financing Receivable, Credit Quality Indicator [Line Items]
Total	5,308,902	5,746,863
Real Estate | Other commercial | Pass
Financing Receivable, Credit Quality Indicator [Line Items]
2021 (YTD)	712,198	1,563,245
2020	825,416	525,750
2019	361,642	375,303
2018	305,381	518,534
2017	484,230	372,679
2016 and Prior	549,452	284,098
Lines of Credit (“LOC”) Amortized Cost Basis	1,410,186	1,445,428
LOC Converted to Term Loans Amortized Cost Basis	217,398	181,949
Total	4,865,903	5,266,986
Real Estate | Other commercial | Special mention
Financing Receivable, Credit Quality Indicator [Line Items]
2021 (YTD)	32,752	100,085
2020	57,067	4,346
2019	2,833	10,738
2018	7,666	19,943
2017	34,164	26,245
2016 and Prior	8,723	10,608
Lines of Credit (“LOC”) Amortized Cost Basis	91,572	63,305
LOC Converted to Term Loans Amortized Cost Basis	7,194	23,435
Total	241,971	258,705
Real Estate | Other commercial | Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
2021 (YTD)	33,001	66,737
2020	25,289	9,418
2019	6,172	24,380
2018	9,800	14,067
2017	33,130	3,744
2016 and Prior	22,630	11,158
Lines of Credit (“LOC”) Amortized Cost Basis	50,335	52,182
LOC Converted to Term Loans Amortized Cost Basis	20,671	39,486
Total	201,028	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)	777,951	1,730,067
2020	907,772	539,514
2019	370,647	410,421
2018	322,847	552,544
2017	551,524	402,668
2016 and Prior	580,805	305,864
Lines of Credit (“LOC”) Amortized Cost Basis	1,552,093	1,560,915
LOC Converted to Term Loans Amortized Cost Basis	245,263	244,870
Total	5,308,902	5,746,863
Commercial
Financing Receivable, Credit Quality Indicator [Line Items]
Total	2,038,640	2,750,291
Commercial | Commercial
Financing Receivable, Credit Quality Indicator [Line Items]
Total	1,821,905	2,574,386
Commercial | Commercial | Pass
Financing Receivable, Credit Quality Indicator [Line Items]
2021 (YTD)	419,739	1,168,085
2020	212,161	154,740
2019	91,328	110,383
2018	66,078	65,757
2017	30,687	35,198
2016 and Prior	44,298	45,568
Lines of Credit (“LOC”) Amortized Cost Basis	852,103	803,751
LOC Converted to Term Loans Amortized Cost Basis	46,186	56,648
Total	1,762,580	2,440,130
Commercial | Commercial | Special mention
Financing Receivable, Credit Quality Indicator [Line Items]
2021 (YTD)	0	5,707
2020	2,438	342
2019	569	465
2018	210	972
2017	252	54
2016 and Prior	384	0
Lines of Credit (“LOC”) Amortized Cost Basis	106	12,318
LOC Converted to Term Loans Amortized Cost Basis	11,016	22,546
Total	14,975	42,404
Commercial | Commercial | Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
2021 (YTD)	3,726	23,227
2020	18,934	4,495
2019	2,016	1,586
2018	1,512	730
2017	688	276
2016 and Prior	978	334
Lines of Credit (“LOC”) Amortized Cost Basis	10,048	53,682
LOC Converted to Term Loans Amortized Cost Basis	6,448	7,522
Total	44,350	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)	423,465	1,197,019
2020	233,533	159,577
2019	93,913	112,434
2018	67,800	67,459
2017	31,627	35,528
2016 and Prior	45,660	45,902
Lines of Credit (“LOC”) Amortized Cost Basis	862,257	869,751
LOC Converted to Term Loans Amortized Cost Basis	63,650	86,716
Total	1,821,905	2,574,386
Commercial | Agricultural
Financing Receivable, Credit Quality Indicator [Line Items]
Total	216,735	175,905
Commercial | Agricultural | Pass
Financing Receivable, Credit Quality Indicator [Line Items]
2021 (YTD)	27,000	36,128
2020	22,841	19,144
2019	11,726	10,014
2018	4,599	4,671
2017	2,688	1,916
2016 and Prior	655	340
Lines of Credit (“LOC”) Amortized Cost Basis	144,909	101,238
LOC Converted to Term Loans Amortized Cost Basis	1,447	1,560
Total	215,865	175,011
Commercial | Agricultural | Special mention
Financing Receivable, Credit Quality Indicator [Line Items]
2021 (YTD)	0	0
2020	0	79
2019	0	13
2018	9	299
2017	0	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	9	431
Commercial | Agricultural | Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
2021 (YTD)	192	86
2020	70	101
2019	99	64
2018	254	47
2017	68	12
2016 and Prior	9	10
Lines of Credit (“LOC”) Amortized Cost Basis	99	68
LOC Converted to Term Loans Amortized Cost Basis	70	75
Total	861	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)	27,192	36,214
2020	22,911	19,324
2019	11,825	10,091
2018	4,862	5,017
2017	2,756	1,928
2016 and Prior	664	356
Lines of Credit (“LOC”) Amortized Cost Basis	145,008	101,340
LOC Converted to Term Loans Amortized Cost Basis	1,517	1,635
Total	216,735	175,905
Other
Financing Receivable, Credit Quality Indicator [Line Items]
Total	348,868	535,591
Current
Financing Receivable, Credit Quality Indicator [Line Items]
Total	10,781,761	12,826,637
Current | Consumer
Financing Receivable, Credit Quality Indicator [Line Items]
Total	356,357	387,187
Current | 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	174,880	187,881
LOC Converted to Term Loans Amortized Cost Basis	0	0
Total	174,880	187,881
Current | Consumer | Other consumer
Financing Receivable, Credit Quality Indicator [Line Items]
2021 (YTD)	105,415	69,334
2020	26,334	44,215
2019	15,158	27,525
2018	8,396	21,995
2017	7,051	19,023
2016 and Prior	5,138	2,530
Lines of Credit (“LOC”) Amortized Cost Basis	13,985	14,684
LOC Converted to Term Loans Amortized Cost Basis	0	0
Total	181,477	199,306
Current | Real Estate
Financing Receivable, Credit Quality Indicator [Line Items]
Total	8,047,271	9,169,016
Current | Real Estate | Construction and development
Financing Receivable, Credit Quality Indicator [Line Items]
Total	1,226,281	1,591,791
Current | Real Estate | Single family residential
Financing Receivable, Credit Quality Indicator [Line Items]
2021 (YTD)	223,243	473,340
2020	245,410	209,810
2019	152,838	297,308
2018	229,241	235,429
2017	179,874	183,229
2016 and Prior	318,019	236,395
Lines of Credit (“LOC”) Amortized Cost Basis	169,693	196,505
LOC Converted to Term Loans Amortized Cost Basis	9,683	10,592
Total	1,528,001	1,842,608
Current | Real Estate | Other commercial
Financing Receivable, Credit Quality Indicator [Line Items]
Total	5,292,989	5,734,617
Current | Commercial
Financing Receivable, Credit Quality Indicator [Line Items]
Total	2,029,272	2,734,935
Current | Commercial | Commercial
Financing Receivable, Credit Quality Indicator [Line Items]
Total	1,813,136	2,559,443
Current | Commercial | Agricultural
Financing Receivable, Credit Quality Indicator [Line Items]
Total	216,136	175,492
Current | Other
Financing Receivable, Credit Quality Indicator [Line Items]
2021 (YTD)	58	125
2020	4,789	4,260
2019	1,287	27,256
2018	24,108	6,489
2017	5,483	2,628
2016 and Prior	6,111	6,065
Lines of Credit (“LOC”) Amortized Cost Basis	307,025	488,676
LOC Converted to Term Loans Amortized Cost Basis	0	0
Total	348,861	535,499
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	751	708
LOC Converted to Term Loans Amortized Cost Basis	0	0
Total	751	708
30-89 days past due | Consumer | Other consumer
Financing Receivable, Credit Quality Indicator [Line Items]
2021 (YTD)	197	234
2020	148	441
2019	113	327
2018	142	658
2017	184	689
2016 and Prior	129	84
Lines of Credit (“LOC”) Amortized Cost Basis	12	338
LOC Converted to Term Loans Amortized Cost Basis	0	0
Total	925	2,771
30-89 days past due | Real Estate | Single family residential
Financing Receivable, Credit Quality Indicator [Line Items]
2021 (YTD)	0	6,300
2020	217	2,258
2019	1,124	2,593
2018	704	2,610
2017	1,279	2,058
2016 and Prior	2,215	6,050
Lines of Credit (“LOC”) Amortized Cost Basis	1,007	1,781
LOC Converted to Term Loans Amortized Cost Basis	0	76
Total	6,546	23,726
30-89 days past due | Other
Financing Receivable, Credit Quality Indicator [Line Items]
2021 (YTD)	0	59
2020	0	0
2019	0	0
2018	0	0
2017	0	33
2016 and Prior	7	0
Lines of Credit (“LOC”) Amortized Cost Basis	0	0
LOC Converted to Term Loans Amortized Cost Basis	0	0
Total	7	92
90+ days past due
Financing Receivable, Credit Quality Indicator [Line Items]
Total	27,820	35,188
90+ days past due | Consumer
Financing Receivable, Credit Quality Indicator [Line Items]
Total	343	558
90+ 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	253	256
LOC Converted to Term Loans Amortized Cost Basis	0	0
Total	253	256
90+ days past due | Consumer | Other consumer
Financing Receivable, Credit Quality Indicator [Line Items]
2021 (YTD)	0	79
2020	14	58
2019	27	25
2018	9	80
2017	20	40
2016 and Prior	19	12
Lines of Credit (“LOC”) Amortized Cost Basis	1	8
LOC Converted to Term Loans Amortized Cost Basis	0	0
Total	90	302
90+ days past due | Real Estate
Financing Receivable, Credit Quality Indicator [Line Items]
Total	20,379	27,014
90+ days past due | Real Estate | Construction and development
Financing Receivable, Credit Quality Indicator [Line Items]
Total	605	3,089
90+ days past due | Real Estate | Single family residential
Financing Receivable, Credit Quality Indicator [Line Items]
2021 (YTD)	67	557
2020	380	1,853
2019	595	2,735
2018	1,141	2,582
2017	1,528	832
2016 and Prior	1,785	3,852
Lines of Credit (“LOC”) Amortized Cost Basis	586	1,928
LOC Converted to Term Loans Amortized Cost Basis	72	0
Total	6,154	14,339
90+ days past due | Real Estate | Other commercial
Financing Receivable, Credit Quality Indicator [Line Items]
Total	13,620	9,586
90+ days past due | Commercial
Financing Receivable, Credit Quality Indicator [Line Items]
Total	7,098	7,616
90+ days past due | Commercial | Commercial
Financing Receivable, Credit Quality Indicator [Line Items]
Total	6,639	7,429
90+ days past due | Commercial | Agricultural
Financing Receivable, Credit Quality Indicator [Line Items]
Total	459	187
90+ days past due | Other
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
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	175,884	188,845
LOC Converted to Term Loans Amortized Cost Basis	0	0
Total	175,884	188,845
30 + days past due | Consumer | Other consumer
Financing Receivable, Credit Quality Indicator [Line Items]
2021 (YTD)	105,612	69,647
2020	26,496	44,714
2019	15,298	27,877
2018	8,547	22,733
2017	7,255	19,752
2016 and Prior	5,286	2,626
Lines of Credit (“LOC”) Amortized Cost Basis	13,998	15,030
LOC Converted to Term Loans Amortized Cost Basis	0	0
Total	182,492	202,379
30 + days past due | Real Estate | Single family residential
Financing Receivable, Credit Quality Indicator [Line Items]
2021 (YTD)	223,310	480,197
2020	246,007	213,921
2019	154,557	302,636
2018	231,086	240,621
2017	182,681	186,119
2016 and Prior	322,019	246,297
Lines of Credit (“LOC”) Amortized Cost Basis	171,286	200,214
LOC Converted to Term Loans Amortized Cost Basis	9,755	10,668
Total	1,540,701	1,880,673
30 + days past due | Other
Financing Receivable, Credit Quality Indicator [Line Items]
2021 (YTD)	58	184
2020	4,789	4,260
2019	1,287	27,256
2018	24,108	6,489
2017	5,483	2,661
2016 and Prior	6,118	6,065
Lines of Credit (“LOC”) Amortized Cost Basis	307,025	488,676
LOC Converted to Term Loans Amortized Cost Basis	0	0
Total	$ 348,868	$ 535,591