Business Segments - Financial Information by Business Segment (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2025	Jun. 30, 2024	Jun. 30, 2025	Jun. 30, 2024
Segment Reporting Information [Line Items]
Interest and dividend income	$ 336,382	$ 202,993	$ 589,614	$ 398,327
Less: Interest expense	119,613	86,400	214,326	167,767
NET INTEREST INCOME	216,769	116,593	375,288	230,560
Less: Provision for credit losses	3,218	10,541	72,101	14,555
Net interest income after provision for credit losses	213,551	106,052	303,187	216,005
Non-interest income:
Trust fees	9,657	7,303	18,355	15,385
Service charges on deposits	10,484	7,111	19,070	13,895
Digital banking income	7,325	5,040	12,730	9,745
Net swap fee and valuation income	746	1,776	1,706	3,339
Net securities brokerage revenue	3,348	2,601	6,049	5,149
Bank-owned life insurance	3,450	2,791	6,878	4,859
Net securities gains	1,410	135	1,092	672
Net gain on other real estate owned and other assets	111	34	71	188
Mortgage banking income	2,364	1,069	3,504	1,762
Other income	5,062	3,495	9,167	6,990
Less :
Salaries and wages	60,153	43,991	108,730	86,988
Employee benefits	18,857	10,579	31,827	22,763
Net occupancy	8,119	6,309	15,897	12,932
Equipment and software	17,140	10,457	30,190	20,465
Marketing	1,864	2,371	4,246	4,256
FDIC insurance	5,479	3,523	9,666	6,971
Merger-related and restructuring	41,056	3,777	61,066	3,777
Amortization of intangibles	9,204	2,072	13,427	4,164
Segment profit (loss) before provision for income taxes	70,973	35,015	61,309	78,404
Provision for income taxes	13,558	6,099	12,886	13,795
Net income	57,415	28,916	48,423	64,609
Reconciliation of segment (loss) profit
Preferred stock dividends	(2,531)	(2,531)	(5,063)	(5,063)
Net income available to common shareholders	54,884	26,385	43,360	59,546
Operating Segments [Member]
Non-interest income:
Total revenues	257,508	137,407	381,809	277,989
Less :
Net income	57,415	28,916	48,423	64,609
Reconciliation of segment (loss) profit
Preferred stock dividends	(2,531)	(2,531)	(5,063)	(5,063)
Net income available to common shareholders	54,884	26,385	43,360	59,546
Community Banking [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Interest and dividend income	336,382	202,993	589,614	398,327
Less: Interest expense	112,804	81,311	202,453	157,575
NET INTEREST INCOME	223,578	121,682	387,161	240,752
Less: Provision for credit losses	3,218	10,541	72,101	14,555
Net interest income after provision for credit losses	220,360	111,141	315,060	226,197
Non-interest income:
Service charges on deposits	10,484	7,111	19,070	13,895
Digital banking income	7,325	5,040	12,730	9,745
Net swap fee and valuation income	746	1,776	1,706	3,339
Net securities brokerage revenue	3,348	2,601	6,049	5,149
Net insurance services revenue	1,115	980	2,070	1,924
Bank-owned life insurance	3,450	2,791	6,878	4,859
Payment processing fees	805	905	1,696	1,734
Net securities gains	1,410	135	1,092	672
Net gain on other real estate owned and other assets	111	34	71	188
Mortgage banking income	2,364	1,069	3,504	1,762
Other income	2,374	1,610	4,624	3,332
Total revenues	253,892	135,193	374,550	272,796
Less :
Salaries and wages	57,983	42,197	104,598	83,342
Employee benefits	18,307	10,118	30,797	21,818
Net occupancy	8,049	6,257	15,770	12,828
Equipment and software	17,063	10,449	30,056	20,450
Miscellaneous taxes	5,059	3,077	9,292	6,236
Professional services	4,637	2,002	8,407	5,667
Marketing	1,834	2,364	4,196	4,234
FDIC insurance	5,479	3,523	9,666	6,971
Supplies	2,037	1,608	3,722	2,904
Telecommunications	1,541	1,309	2,751	2,572
General administration	2,247	1,564	3,617	2,924
Merger-related and restructuring	40,301	3,777	53,992	3,777
Amortization of intangibles	8,816	2,024	12,999	4,068
Other segment items	4,673	5,671	9,558	9,897
Segment profit (loss) before provision for income taxes	75,866	39,253	75,129	85,108
Provision for income taxes	15,705	6,772	15,815	15,196
Net income	60,161	32,481	59,314	69,912
Trust and Investment Services [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Less: Interest expense	1,500	1,045	2,435	2,073
NET INTEREST INCOME	(1,500)	(1,045)	(2,435)	(2,073)
Net interest income after provision for credit losses	(1,500)	(1,045)	(2,435)	(2,073)
Non-interest income:
Trust fees	7,698	5,305	14,372	11,405
WesMark fees	1,959	1,998	3,983	3,980
Other income	760		760
Total revenues	8,917	6,258	16,680	13,312
Less :
Salaries and wages	2,170	1,794	4,132	3,646
Employee benefits	550	461	1,030	945
Net occupancy	70	52	127	104
Equipment and software	77	8	134	15
Miscellaneous taxes	2	0	3	3
Professional services	166	82	304	158
Marketing	30	7	50	22
Supplies	41	26	94	68
General administration	54	40	82	73
Amortization of intangibles	388	48	428	96
Corporate overhead expenses	2,021	1,376	3,601	2,899
Other segment items	50	50	81	110
Segment profit (loss) before provision for income taxes	3,298	2,314	6,614	5,173
Provision for income taxes	693	486	1,389	1,086
Net income	2,605	1,828	5,225	4,087
Corporate Other [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Less: Interest expense	5,309	4,044	9,438	8,119
NET INTEREST INCOME	(5,309)	(4,044)	(9,438)	(8,119)
Net interest income after provision for credit losses	(5,309)	(4,044)	(9,438)	(8,119)
Non-interest income:
Other income	8		17
Total revenues	(5,301)	(4,044)	(9,421)	(8,119)
Less :
Professional services	1,832	2,509	3,542	3,770
General administration	287	43	417	68
Merger-related and restructuring	755		7,074
Other segment items	16	(44)	(20)	(80)
Segment profit (loss) before provision for income taxes	(8,191)	(6,552)	(20,434)	(11,877)
Provision for income taxes	(2,840)	(1,159)	(4,318)	(2,487)
Net income	$ (5,351)	$ (5,393)	$ (16,116)	$ (9,390)