Loans and Allowance for Credit Losses - Allowance for Credit Losses (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021	Dec. 31, 2021
Accounts Receivable, Allowance for Credit Loss [Roll Forward]
Beginning Balance	$ 92,522	$ 101,309
Charge-offs	(1,623)	(3,765)
Recoveries	489	495
Provision for credit losses	(200)	(1,276)
Ending Balance	91,188	96,763	$ 92,522
Ending balance: individually evaluated for impaired	351	3,107
Ending balance: collectively evaluated for impaired	90,837	93,656
Loans and Leases Receivable, Net of Deferred Income	(6,952,112)	(6,736,894)	(6,839,230)
Ending balance: individually evaluated for impaired	40,695	38,459
Ending balance: collectively evaluated for impaired	6,911,417	6,698,435
Provision for credit losses	1,964	(4,390)
Commercial, financial, agricultural and other [Member]
Accounts Receivable, Allowance for Credit Loss [Roll Forward]
Beginning Balance	18,093	17,187
Charge-offs	(475)	(569)
Recoveries	80	90
Provision for credit losses	3,023	5,093
Ending Balance	20,721	21,801	18,093
Ending balance: individually evaluated for impaired	272	2,506
Ending balance: collectively evaluated for impaired	20,449	19,295
Loans and Leases Receivable, Net of Deferred Income	(1,123,690)	(1,555,671)	(1,173,452)
Ending balance: individually evaluated for impaired	3,179	9,991
Ending balance: collectively evaluated for impaired	1,120,511	1,545,680
Commercial, financial, agricultural and other [Member] | Time and Demand Loans
Accounts Receivable, Allowance for Credit Loss [Roll Forward]
Beginning Balance	15,283	16,838
Charge-offs	(144)	(460)
Recoveries	53	89
Provision for credit losses	3,715	4,960
Ending Balance	18,907	21,427	15,283
Ending balance: individually evaluated for impaired	272	2,506
Ending balance: collectively evaluated for impaired	18,635	18,921
Loans and Leases Receivable, Net of Deferred Income	(992,477)	(1,541,280)	(1,159,524)
Ending balance: individually evaluated for impaired	3,179	9,991
Ending balance: collectively evaluated for impaired	989,298	1,531,289
Commercial, financial, agricultural and other [Member] | Commercial Credit Cards
Accounts Receivable, Allowance for Credit Loss [Roll Forward]
Beginning Balance	247	349
Charge-offs	(19)	(109)
Recoveries	1	1
Provision for credit losses	113	133
Ending Balance	342	374	247
Ending balance: individually evaluated for impaired	0	0
Ending balance: collectively evaluated for impaired	342	374
Loans and Leases Receivable, Net of Deferred Income	(13,675)	(14,391)	(13,928)
Ending balance: individually evaluated for impaired	0	0
Ending balance: collectively evaluated for impaired	13,675	14,391
Commercial, financial, agricultural and other [Member] | Time and Demand Loans Other
Accounts Receivable, Allowance for Credit Loss [Roll Forward]
Beginning Balance	2,563
Charge-offs	(312)
Recoveries	26
Provision for credit losses	(836)
Ending Balance	1,441		2,563
Ending balance: individually evaluated for impaired	0
Ending balance: collectively evaluated for impaired	1,441
Loans and Leases Receivable, Net of Deferred Income	(115,033)
Ending balance: individually evaluated for impaired	0
Ending balance: collectively evaluated for impaired	115,033
Commercial, financial, agricultural and other [Member] | Equipment Finance
Accounts Receivable, Allowance for Credit Loss [Roll Forward]
Beginning Balance	0
Charge-offs	0
Recoveries	0
Provision for credit losses	31
Ending Balance	31		0
Ending balance: individually evaluated for impaired	0
Ending balance: collectively evaluated for impaired	31
Loans and Leases Receivable, Net of Deferred Income	(2,505)
Ending balance: individually evaluated for impaired	0
Ending balance: collectively evaluated for impaired	2,505
Residential real estate [Member]
Accounts Receivable, Allowance for Credit Loss [Roll Forward]
Beginning Balance	12,625	14,358
Charge-offs	(139)	(105)
Recoveries	29	37
Provision for credit losses	4,213	(1,461)
Ending Balance	16,728	12,829	12,625
Ending balance: individually evaluated for impaired	0	0
Ending balance: collectively evaluated for impaired	16,728	12,829
Loans and Leases Receivable, Net of Deferred Income	(2,006,221)	(1,756,615)	(1,920,250)
Ending balance: individually evaluated for impaired	253	1,055
Ending balance: collectively evaluated for impaired	2,005,968	1,755,560
Residential real estate [Member] | Senior Lien
Accounts Receivable, Allowance for Credit Loss [Roll Forward]
Beginning Balance	7,459	7,919
Charge-offs	(40)	(23)
Recoveries	23	23
Provision for credit losses	3,683	(692)
Ending Balance	11,125	7,227	7,459
Ending balance: individually evaluated for impaired	0	0
Ending balance: collectively evaluated for impaired	11,125	7,227
Loans and Leases Receivable, Net of Deferred Income	(1,381,742)	(1,152,314)	(1,299,534)
Ending balance: individually evaluated for impaired	0	512
Ending balance: collectively evaluated for impaired	1,381,742	1,151,802
Residential real estate [Member] | Junior Lien
Accounts Receivable, Allowance for Credit Loss [Roll Forward]
Beginning Balance	5,166	6,439
Charge-offs	(99)	(82)
Recoveries	6	14
Provision for credit losses	530	(769)
Ending Balance	5,603	5,602	5,166
Ending balance: individually evaluated for impaired	0	0
Ending balance: collectively evaluated for impaired	5,603	5,602
Loans and Leases Receivable, Net of Deferred Income	(624,479)	(604,301)	(620,716)
Ending balance: individually evaluated for impaired	253	543
Ending balance: collectively evaluated for impaired	624,226	603,758
Commercial Real Estate [Member]
Accounts Receivable, Allowance for Credit Loss [Roll Forward]
Beginning Balance	33,376	41,953
Charge-offs	0	(1,550)
Recoveries	14	39
Provision for credit losses	314	(2,774)
Ending Balance	33,704	37,668	33,376
Ending balance: individually evaluated for impaired	79	601
Ending balance: collectively evaluated for impaired	33,625	37,067
Loans and Leases Receivable, Net of Deferred Income	(2,344,281)	(2,167,506)	(2,251,097)
Ending balance: individually evaluated for impaired	37,263	27,413
Ending balance: collectively evaluated for impaired	2,307,018	2,140,093
Commercial Real Estate [Member] | Multifamily
Accounts Receivable, Allowance for Credit Loss [Roll Forward]
Beginning Balance	3,561	6,240
Charge-offs	0	(1)
Recoveries	0	0
Provision for credit losses	49	(1,988)
Ending Balance	3,610	4,251	3,561
Ending balance: individually evaluated for impaired	79	115
Ending balance: collectively evaluated for impaired	3,531	4,136
Loans and Leases Receivable, Net of Deferred Income	(401,581)	(363,604)	(385,432)
Ending balance: individually evaluated for impaired	14,909	459
Ending balance: collectively evaluated for impaired	386,672	363,145
Commercial Real Estate [Member] | Nonowner Occupied Commercial Real Estate
Accounts Receivable, Allowance for Credit Loss [Roll Forward]
Beginning Balance	24,838	28,414
Charge-offs	0	(1,549)
Recoveries	5	39
Provision for credit losses	(1,576)	985
Ending Balance	23,267	27,889	24,838
Ending balance: individually evaluated for impaired	0	459
Ending balance: collectively evaluated for impaired	23,267	27,430
Loans and Leases Receivable, Net of Deferred Income	(1,516,518)	(1,393,968)	(1,465,247)
Ending balance: individually evaluated for impaired	21,425	24,883
Ending balance: collectively evaluated for impaired	1,495,093	1,369,085
Commercial Real Estate [Member] | Owner Occupied Commercial Real Estate
Accounts Receivable, Allowance for Credit Loss [Roll Forward]
Beginning Balance	4,977	7,299
Charge-offs	0	0
Recoveries	9	0
Provision for credit losses	1,841	(1,771)
Ending Balance	6,827	5,528	4,977
Ending balance: individually evaluated for impaired	0	27
Ending balance: collectively evaluated for impaired	6,827	5,501
Loans and Leases Receivable, Net of Deferred Income	(426,182)	(409,934)	(400,418)
Ending balance: individually evaluated for impaired	929	2,071
Ending balance: collectively evaluated for impaired	425,253	407,863
Loans to individuals [Member]
Accounts Receivable, Allowance for Credit Loss [Roll Forward]
Beginning Balance	24,208	19,845
Charge-offs	(1,009)	(1,541)
Recoveries	366	329
Provision for credit losses	(8,460)	1,811
Ending Balance	15,105	20,444	24,208
Ending balance: individually evaluated for impaired	0	0
Ending balance: collectively evaluated for impaired	15,105	20,444
Loans and Leases Receivable, Net of Deferred Income	(1,078,932)	(852,522)	(999,975)
Ending balance: individually evaluated for impaired	0	0
Ending balance: collectively evaluated for impaired	1,078,932	852,522
Loans to individuals [Member] | Automobiles
Accounts Receivable, Allowance for Credit Loss [Roll Forward]
Beginning Balance	21,392	16,133
Charge-offs	(552)	(680)
Recoveries	255	181
Provision for credit losses	(8,460)	1,254
Ending Balance	12,635	16,888	21,392
Ending balance: individually evaluated for impaired	0	0
Ending balance: collectively evaluated for impaired	12,635	16,888
Loans and Leases Receivable, Net of Deferred Income	(984,001)	(759,061)	(901,280)
Ending balance: individually evaluated for impaired	0	0
Ending balance: collectively evaluated for impaired	984,001	759,061
Loans to individuals [Member] | Consumer Credit Cards
Accounts Receivable, Allowance for Credit Loss [Roll Forward]
Beginning Balance	496	635
Charge-offs	(109)	(168)
Recoveries	24	17
Provision for credit losses	(29)	205
Ending Balance	382	689	496
Ending balance: individually evaluated for impaired	0	0
Ending balance: collectively evaluated for impaired	382	689
Loans and Leases Receivable, Net of Deferred Income	(10,675)	(10,901)	(11,151)
Ending balance: individually evaluated for impaired	0	0
Ending balance: collectively evaluated for impaired	10,675	10,901
Loans to individuals [Member] | Other Consumer Loans
Accounts Receivable, Allowance for Credit Loss [Roll Forward]
Beginning Balance	2,320	3,077
Charge-offs	(348)	(693)
Recoveries	87	131
Provision for credit losses	29	352
Ending Balance	2,088	2,867	2,320
Ending balance: individually evaluated for impaired	0	0
Ending balance: collectively evaluated for impaired	2,088	2,867
Loans and Leases Receivable, Net of Deferred Income	(84,256)	(82,560)	(87,544)
Ending balance: individually evaluated for impaired	0	0
Ending balance: collectively evaluated for impaired	84,256	82,560
Real estate construction [Member]
Accounts Receivable, Allowance for Credit Loss [Roll Forward]
Beginning Balance	4,220	7,966
Charge-offs	0	0
Recoveries	0	0
Provision for credit losses	710	(3,945)
Ending Balance	4,930	4,021	4,220
Ending balance: individually evaluated for impaired	0	0
Ending balance: collectively evaluated for impaired	4,930	4,021
Loans and Leases Receivable, Net of Deferred Income	(398,988)	(404,580)	(494,456)
Ending balance: individually evaluated for impaired	0	0
Ending balance: collectively evaluated for impaired	398,988	$ 404,580
Real estate construction [Member] | Construction Residential
Accounts Receivable, Allowance for Credit Loss [Roll Forward]
Beginning Balance	942
Charge-offs	0
Recoveries	0
Provision for credit losses	813
Ending Balance	1,755		942
Ending balance: individually evaluated for impaired	0
Ending balance: collectively evaluated for impaired	1,755
Loans and Leases Receivable, Net of Deferred Income	(91,577)
Ending balance: individually evaluated for impaired	0
Ending balance: collectively evaluated for impaired	91,577
Real estate construction [Member] | Construction Other
Accounts Receivable, Allowance for Credit Loss [Roll Forward]
Beginning Balance	3,278
Charge-offs	0
Recoveries	0
Provision for credit losses	(103)
Ending Balance	3,175		$ 3,278
Ending balance: individually evaluated for impaired	0
Ending balance: collectively evaluated for impaired	3,175
Loans and Leases Receivable, Net of Deferred Income	(307,411)
Ending balance: individually evaluated for impaired	0
Ending balance: collectively evaluated for impaired	$ 307,411