Allowance for Credit Losses, Credit Quality and Other - Summary of Most Recent Analysis Performed, Risk Category of Loans by Class of Loans and Writeoffs (Detail) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
Sep. 30, 2024	Dec. 31, 2023
Financing Receivable Allowance For Credit Losses [Line Items]
Year One	$ 1,557,221	$ 2,138,730
Year Two	2,239,000	3,341,500
Year Three	3,248,020	2,083,044
Year Four	1,679,539	1,132,926
Year Five	923,973	872,429
Prior	3,245,462	2,908,528
Revolving Loans Amortized Cost Basis	1,930,764	1,947,571
Total	14,823,979	14,424,728
Writeoffs, Year One	2,206	3,252
Writeoffs, Year Two	715	490
Writeoffs, Year Three	264	1,351
Writeoffs, Year Four	1,161	1,072
Writeoffs, Year Five	277	2,878
Writeoffs, Prior	1,199	6,357
Writeoffs, Revolving	3,255	655
Writeoffs, Total	9,077	16,055
Commercial real estate loans
Financing Receivable Allowance For Credit Losses [Line Items]
Year One	935,554	930,022
Year Two	1,127,650	2,146,390
Year Three	2,023,558	1,262,133
Year Four	1,041,573	626,807
Year Five	486,086	481,164
Prior	2,071,625	1,905,250
Revolving Loans Amortized Cost Basis	887,874	816,391
Total	8,573,920	8,168,157
Commercial real estate loans \| Non-farm/non-residential
Financing Receivable Allowance For Credit Losses [Line Items]
Year One	218,451	388,831
Year Two	481,457	1,150,598
Year Three	1,068,460	830,588
Year Four	836,245	491,298
Year Five	401,616	404,822
Prior	1,910,085	1,747,135
Revolving Loans Amortized Cost Basis	580,222	536,682
Total	5,496,536	5,549,954
Writeoffs, Year One	0	0
Writeoffs, Year Two	0	0
Writeoffs, Year Three	0	0
Writeoffs, Year Four	780	0
Writeoffs, Year Five	1	1,826
Writeoffs, Prior	383	502
Writeoffs, Revolving	0	0
Writeoffs, Total	1,164	2,328
Commercial real estate loans \| Construction/land development
Financing Receivable Allowance For Credit Losses [Line Items]
Year One	667,797	501,215
Year Two	601,615	926,208
Year Three	894,340	384,657
Year Four	166,388	88,901
Year Five	51,652	55,857
Prior	88,489	81,216
Revolving Loans Amortized Cost Basis	271,138	254,993
Total	2,741,419	2,293,047
Writeoffs, Year One	0	0
Writeoffs, Year Two	0	2
Writeoffs, Year Three	0	168
Writeoffs, Year Four	48	5
Writeoffs, Year Five	33	0
Writeoffs, Prior	0	88
Writeoffs, Revolving	0	0
Writeoffs, Total	81	263
Commercial real estate loans \| Agricultural
Financing Receivable Allowance For Credit Losses [Line Items]
Year One	49,306	39,976
Year Two	44,578	69,584
Year Three	60,758	46,888
Year Four	38,940	46,608
Year Five	32,818	20,485
Prior	73,051	76,899
Revolving Loans Amortized Cost Basis	36,514	24,716
Total	335,965	325,156
Writeoffs, Year One	0	0
Writeoffs, Year Two	0	0
Writeoffs, Year Three	0	0
Writeoffs, Year Four	0	0
Writeoffs, Year Five	0	1
Writeoffs, Prior	0	6
Writeoffs, Revolving	0	0
Writeoffs, Total	0	7
Residential real estate loans \| Residential 1-4 family
Financing Receivable Allowance For Credit Losses [Line Items]
Year One	187,704	261,784
Year Two	256,902	409,197
Year Three	422,537	300,563
Year Four	261,251	171,122
Year Five	156,691	111,327
Prior	449,644	403,729
Revolving Loans Amortized Cost Basis	197,623	186,538
Total	1,932,352	1,844,260
Writeoffs, Year One	0	0
Writeoffs, Year Two	1	29
Writeoffs, Year Three	100	28
Writeoffs, Year Four	1	73
Writeoffs, Year Five	26	13
Writeoffs, Prior	132	126
Writeoffs, Revolving	0	0
Writeoffs, Total	260	269
Residential real estate loans \| Multifamily residential
Financing Receivable Allowance For Credit Losses [Line Items]
Year One	1,876	3,983
Year Two	11,822	87,012
Year Three	185,829	107,301
Year Four	47,043	108,702
Year Five	111,781	39,815
Prior	97,878	74,564
Revolving Loans Amortized Cost Basis	26,419	14,359
Total	482,648	435,736
Total real estate
Financing Receivable Allowance For Credit Losses [Line Items]
Year One	1,125,134	1,195,789
Year Two	1,396,374	2,642,599
Year Three	2,631,924	1,669,997
Year Four	1,349,867	906,631
Year Five	754,558	632,306
Prior	2,619,147	2,383,543
Revolving Loans Amortized Cost Basis	1,111,916	1,017,288
Total	10,988,920	10,448,153
Writeoffs, Year One	0	0
Writeoffs, Year Two	1	31
Writeoffs, Year Three	100	196
Writeoffs, Year Four	829	78
Writeoffs, Year Five	60	1,840
Writeoffs, Prior	515	722
Writeoffs, Revolving	0	0
Writeoffs, Total	1,505	2,867
Consumer
Financing Receivable Allowance For Credit Losses [Line Items]
Year One	219,061	255,930
Year Two	226,131	257,588
Year Three	228,528	216,645
Year Four	184,366	109,981
Year Five	92,448	110,406
Prior	265,784	200,071
Revolving Loans Amortized Cost Basis	2,879	3,069
Total	1,219,197	1,153,690
Writeoffs, Year One	4	0
Writeoffs, Year Two	86	51
Writeoffs, Year Three	75	44
Writeoffs, Year Four	40	98
Writeoffs, Year Five	109	63
Writeoffs, Prior	485	263
Writeoffs, Revolving	0	25
Writeoffs, Total	799	544
Commercial and industrial
Financing Receivable Allowance For Credit Losses [Line Items]
Year One	133,512	619,371
Year Two	559,408	385,376
Year Three	339,418	156,919
Year Four	110,948	88,094
Year Five	51,754	114,522
Prior	311,045	276,677
Revolving Loans Amortized Cost Basis	578,582	684,032
Total	2,084,667	2,324,991
Writeoffs, Year One	0	0
Writeoffs, Year Two	557	407
Writeoffs, Year Three	89	1,110
Writeoffs, Year Four	292	894
Writeoffs, Year Five	108	911
Writeoffs, Prior	199	5,369
Writeoffs, Revolving	3,255	466
Writeoffs, Total	4,500	9,157
Agricultural & other
Financing Receivable Allowance For Credit Losses [Line Items]
Year One	79,514	67,640
Year Two	57,087	55,937
Year Three	48,150	39,483
Year Four	34,358	28,220
Year Five	25,213	15,195
Prior	49,486	48,237
Revolving Loans Amortized Cost Basis	237,387	243,182
Total	531,195	497,894
Writeoffs, Year One	2,202	3,252
Writeoffs, Year Two	71	1
Writeoffs, Year Three	0	1
Writeoffs, Year Four	0	2
Writeoffs, Year Five	0	64
Writeoffs, Prior	0	3
Writeoffs, Revolving	0	164
Writeoffs, Total	2,273	3,487
Risk rating 1 \| Commercial real estate loans \| Non-farm/non-residential
Financing Receivable Allowance For Credit Losses [Line Items]
Year One	0	0
Year Two	0	0
Year Three	0	0
Year Four	0	0
Year Five	0	232
Prior	331	116
Revolving Loans Amortized Cost Basis	74	55
Total	405	403
Risk rating 1 \| Commercial real estate loans \| Construction/land development
Financing Receivable Allowance For Credit Losses [Line Items]
Year One	0	0
Year Two	0	0
Year Three	0	10
Year Four	10	0
Year Five	0	0
Prior	0	0
Revolving Loans Amortized Cost Basis	0	0
Total	10	10
Risk rating 1 \| Commercial real estate loans \| Agricultural
Financing Receivable Allowance For Credit Losses [Line Items]
Year One	700	0
Year Two	0	1,605
Year Three	1,462	0
Year Four	0	0
Year Five	0	0
Prior	0	0
Revolving Loans Amortized Cost Basis	0	0
Total	2,162	1,605
Risk rating 1 \| Residential real estate loans \| Residential 1-4 family
Financing Receivable Allowance For Credit Losses [Line Items]
Year One	0	0
Year Two	0	0
Year Three	0	0
Year Four	0	0
Year Five	0	0
Prior	92	144
Revolving Loans Amortized Cost Basis	2	2
Total	94	146
Risk rating 1 \| Residential real estate loans \| Multifamily residential
Financing Receivable Allowance For Credit Losses [Line Items]
Year One	0	0
Year Two	0	0
Year Three	0	0
Year Four	0	0
Year Five	0	0
Prior	0	0
Revolving Loans Amortized Cost Basis	0	0
Total	0	0
Risk rating 1 \| Total real estate
Financing Receivable Allowance For Credit Losses [Line Items]
Year One		1,195,789
Year Two		2,642,599
Year Three		1,669,997
Year Four		906,631
Year Five		632,306
Prior		2,383,543
Revolving Loans Amortized Cost Basis		1,017,288
Total		10,448,153
Risk rating 1 \| Consumer
Financing Receivable Allowance For Credit Losses [Line Items]
Year One	4,480	5,195
Year Two	2,582	2,952
Year Three	1,667	2,002
Year Four	1,291	839
Year Five	642	355
Prior	1,064	1,114
Revolving Loans Amortized Cost Basis	1,506	1,580
Total	13,232	14,037
Risk rating 1 \| Commercial and industrial
Financing Receivable Allowance For Credit Losses [Line Items]
Year One	3,402	3,757
Year Two	1,207	918
Year Three	793	1,120
Year Four	651	236
Year Five	219	121
Prior	21,338	20,835
Revolving Loans Amortized Cost Basis	10,740	12,644
Total	38,350	39,631
Risk rating 1 \| Agricultural & other
Financing Receivable Allowance For Credit Losses [Line Items]
Year One	643	408
Year Two	378	131
Year Three	222	16
Year Four	16	105
Year Five	105	0
Prior	0	2
Revolving Loans Amortized Cost Basis	782	563
Total	2,146	1,225
Risk rating 2 \| Commercial real estate loans \| Non-farm/non-residential
Financing Receivable Allowance For Credit Losses [Line Items]
Year One	0	0
Year Two	0	0
Year Three	0	0
Year Four	0	0
Year Five	0	111
Prior	0	0
Revolving Loans Amortized Cost Basis	0	0
Total	0	111
Risk rating 2 \| Commercial real estate loans \| Construction/land development
Financing Receivable Allowance For Credit Losses [Line Items]
Year One	0	759
Year Two	136	0
Year Three	0	0
Year Four	0	0
Year Five	0	0
Prior	165	186
Revolving Loans Amortized Cost Basis	37	0
Total	338	945
Risk rating 2 \| Commercial real estate loans \| Agricultural
Financing Receivable Allowance For Credit Losses [Line Items]
Year One	278	247
Year Two	241	0
Year Three	0	1,936
Year Four	1,853	0
Year Five	0	0
Prior	0	0
Revolving Loans Amortized Cost Basis	0	0
Total	2,372	2,183
Risk rating 2 \| Residential real estate loans \| Residential 1-4 family
Financing Receivable Allowance For Credit Losses [Line Items]
Year One	0	259
Year Two	230	0
Year Three	0	0
Year Four	0	0
Year Five	0	0
Prior	11	20
Revolving Loans Amortized Cost Basis	5	1
Total	246	280
Risk rating 2 \| Residential real estate loans \| Multifamily residential
Financing Receivable Allowance For Credit Losses [Line Items]
Year One	0	0
Year Two	0	0
Year Three	0	0
Year Four	0	0
Year Five	0	0
Prior	0	0
Revolving Loans Amortized Cost Basis	0	0
Total	0	0
Risk rating 2 \| Consumer
Financing Receivable Allowance For Credit Losses [Line Items]
Year One	0	0
Year Two	0	0
Year Three	0	0
Year Four	0	0
Year Five	0	126
Prior	150	54
Revolving Loans Amortized Cost Basis	0	0
Total	150	180
Risk rating 2 \| Commercial and industrial
Financing Receivable Allowance For Credit Losses [Line Items]
Year One	48	174
Year Two	132	1,293
Year Three	1,074	220
Year Four	185	12
Year Five	5	164
Prior	19	218
Revolving Loans Amortized Cost Basis	2,142	963
Total	3,605	3,044
Risk rating 2 \| Agricultural & other
Financing Receivable Allowance For Credit Losses [Line Items]
Year One	537	396
Year Two	304	28
Year Three	28	1
Year Four	0	0
Year Five	0	1,181
Prior	0	100
Revolving Loans Amortized Cost Basis	2,447	693
Total	3,316	2,399
Risk rating 3 \| Commercial real estate loans \| Non-farm/non-residential
Financing Receivable Allowance For Credit Losses [Line Items]
Year One	163,941	305,742
Year Two	312,252	584,860
Year Three	601,970	568,413
Year Four	562,043	243,177
Year Five	230,931	216,746
Prior	1,021,405	934,111
Revolving Loans Amortized Cost Basis	256,875	440,414
Total	3,149,417	3,293,463
Risk rating 3 \| Commercial real estate loans \| Construction/land development
Financing Receivable Allowance For Credit Losses [Line Items]
Year One	535,815	300,941
Year Two	411,289	499,984
Year Three	424,306	130,342
Year Four	84,734	62,134
Year Five	41,633	22,656
Prior	62,671	56,180
Revolving Loans Amortized Cost Basis	65,049	44,603
Total	1,625,497	1,116,840
Risk rating 3 \| Commercial real estate loans \| Agricultural
Financing Receivable Allowance For Credit Losses [Line Items]
Year One	35,210	30,252
Year Two	34,159	43,291
Year Three	32,111	22,919
Year Four	15,598	25,992
Year Five	21,231	10,678
Prior	44,924	43,284
Revolving Loans Amortized Cost Basis	31,107	20,104
Total	214,340	196,520
Risk rating 3 \| Residential real estate loans \| Residential 1-4 family
Financing Receivable Allowance For Credit Losses [Line Items]
Year One	181,112	246,462
Year Two	232,086	366,149
Year Three	368,096	241,985
Year Four	232,800	145,339
Year Five	131,378	93,751
Prior	361,150	324,569
Revolving Loans Amortized Cost Basis	114,114	122,950
Total	1,620,736	1,541,205
Risk rating 3 \| Residential real estate loans \| Multifamily residential
Financing Receivable Allowance For Credit Losses [Line Items]
Year One	1,876	3,314
Year Two	11,133	9,827
Year Three	34,052	37,755
Year Four	36,223	44,407
Year Five	52,758	31,436
Prior	76,818	53,068
Revolving Loans Amortized Cost Basis	11,449	6,537
Total	224,309	186,344
Risk rating 3 \| Consumer
Financing Receivable Allowance For Credit Losses [Line Items]
Year One	210,168	240,897
Year Two	213,187	245,543
Year Three	217,177	211,312
Year Four	181,131	108,009
Year Five	90,901	108,063
Prior	252,855	191,220
Revolving Loans Amortized Cost Basis	1,124	1,264
Total	1,166,543	1,106,308
Risk rating 3 \| Commercial and industrial
Financing Receivable Allowance For Credit Losses [Line Items]
Year One	72,780	487,896
Year Two	511,791	272,608
Year Three	239,265	78,507
Year Four	62,304	50,340
Year Five	42,767	77,761
Prior	210,038	170,610
Revolving Loans Amortized Cost Basis	205,363	227,043
Total	1,344,308	1,364,765
Risk rating 3 \| Agricultural & other
Financing Receivable Allowance For Credit Losses [Line Items]
Year One	45,944	52,758
Year Two	51,932	45,796
Year Three	39,142	31,378
Year Four	27,332	26,918
Year Five	24,600	3,059
Prior	32,955	43,984
Revolving Loans Amortized Cost Basis	106,271	145,419
Total	328,176	349,312
Risk rating 4 \| Commercial real estate loans \| Non-farm/non-residential
Financing Receivable Allowance For Credit Losses [Line Items]
Year One	54,483	83,089
Year Two	169,205	557,540
Year Three	457,070	242,217
Year Four	268,482	224,378
Year Five	145,758	149,258
Prior	665,513	590,864
Revolving Loans Amortized Cost Basis	322,795	95,360
Total	2,083,306	1,942,706
Risk rating 4 \| Commercial real estate loans \| Construction/land development
Financing Receivable Allowance For Credit Losses [Line Items]
Year One	131,982	198,874
Year Two	189,494	417,244
Year Three	466,044	252,602
Year Four	79,663	22,713
Year Five	9,720	32,342
Prior	24,720	24,527
Revolving Loans Amortized Cost Basis	205,071	209,063
Total	1,106,694	1,157,365
Risk rating 4 \| Commercial real estate loans \| Agricultural
Financing Receivable Allowance For Credit Losses [Line Items]
Year One	13,118	9,477
Year Two	10,178	24,688
Year Three	27,185	20,358
Year Four	19,868	19,532
Year Five	10,503	7,873
Prior	26,221	32,692
Revolving Loans Amortized Cost Basis	5,214	4,612
Total	112,287	119,232
Risk rating 4 \| Residential real estate loans \| Residential 1-4 family
Financing Receivable Allowance For Credit Losses [Line Items]
Year One	6,592	14,992
Year Two	22,038	37,444
Year Three	44,936	55,406
Year Four	24,590	21,240
Year Five	20,640	13,313
Prior	72,339	67,084
Revolving Loans Amortized Cost Basis	82,201	62,356
Total	273,336	271,835
Risk rating 4 \| Residential real estate loans \| Multifamily residential
Financing Receivable Allowance For Credit Losses [Line Items]
Year One	0	669
Year Two	689	77,185
Year Three	130,725	69,546
Year Four	10,228	64,295
Year Five	59,023	8,116
Prior	20,830	18,490
Revolving Loans Amortized Cost Basis	14,970	7,822
Total	236,465	246,123
Risk rating 4 \| Consumer
Financing Receivable Allowance For Credit Losses [Line Items]
Year One	4,342	9,597
Year Two	4,633	7,534
Year Three	5,151	2,479
Year Four	1,381	69
Year Five	166	109
Prior	5,688	6,073
Revolving Loans Amortized Cost Basis	184	214
Total	21,545	26,075
Risk rating 4 \| Commercial and industrial
Financing Receivable Allowance For Credit Losses [Line Items]
Year One	57,244	115,025
Year Two	34,109	34,474
Year Three	29,322	55,812
Year Four	29,917	33,000
Year Five	8,695	27,189
Prior	66,115	71,854

Allowance for Credit Losses, Credit Quality and Other - Summary of Most Recent Analysis Performed, Risk Category of Loans by Class of Loans and Writeoffs (Detail) - USD ($)
$ in Thousands