Revenue Recognition - Summary of Revenue Recognition (Detail) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021
Schedule Of Revenue Recognition [Line Items]
Total net securities brokerage revenue	$ 2,491,000	$ 1,965,000	$ 6,969,000	$ 5,318,000
Debit card sponsorship income	0	0	0	646,000
Electronic banking fees	4,808,000	5,427,000	15,307,000	14,853,000
Mortgage banking income	1,257,000	4,563,000	4,508,000	16,656,000
Net gain (loss) on other real estate owned and other assets	2,040,000	785,000	(68,000)	4,974,000
Total Service Charges on Deposits [Member]
Schedule Of Revenue Recognition [Line Items]
Total trust fees/Total service charges on deposits	6,942,000	6,050,000	19,520,000	15,820,000
Trust Account fees [Member]
Schedule Of Revenue Recognition [Line Items]
Total trust fees/Total service charges on deposits	4,456,000	4,768,000	$ 14,413,000	14,792,000
Point of revenue recognition			Over time
WesMark Fees [Member]
Schedule Of Revenue Recognition [Line Items]
Total trust fees/Total service charges on deposits	2,061,000	2,521,000	$ 6,466,000	7,277,000
Point of revenue recognition			Over time
Total Trust Fees [Member]
Schedule Of Revenue Recognition [Line Items]
Total trust fees/Total service charges on deposits	6,517,000	7,289,000	$ 20,879,000	22,069,000
Commercial Banking Fees [Member]
Schedule Of Revenue Recognition [Line Items]
Total trust fees/Total service charges on deposits	606,000	464,000	$ 1,776,000	1,629,000
Point of revenue recognition			Over time
Personal Service Charges [Member]
Schedule Of Revenue Recognition [Line Items]
Total trust fees/Total service charges on deposits	6,336,000	5,586,000	$ 17,744,000	14,191,000
Point of revenue recognition			At a point in time and over time
Annuity Commissions [Member]
Schedule Of Revenue Recognition [Line Items]
Total net securities brokerage revenue	1,932,000	1,169,000	$ 5,193,000	3,237,000
Point of revenue recognition			At a point in time
Equity And Debt Security Trades [Member]
Schedule Of Revenue Recognition [Line Items]
Total net securities brokerage revenue	29,000	73,000	$ 94,000	206,000
Point of revenue recognition			At a point in time
Managed Money [Member]
Schedule Of Revenue Recognition [Line Items]
Total net securities brokerage revenue	290,000	311,000	$ 944,000	885,000
Point of revenue recognition			Over time
Trail Commissions [Member]
Schedule Of Revenue Recognition [Line Items]
Total net securities brokerage revenue	240,000	412,000	$ 738,000	990,000
Point of revenue recognition			Over time
Payment Processing Fees [Member]
Schedule Of Revenue Recognition [Line Items]
Payment Processing Fees	$ 818,000	$ 773,000	$ 2,436,000	$ 2,234,000
Point of revenue recognition			At a point in time and over time
Debit Card Sponsorship Income [Member]
Schedule Of Revenue Recognition [Line Items]
Point of revenue recognition			At a point in time and over time
Electronic Banking Fees [Member]
Schedule Of Revenue Recognition [Line Items]
Point of revenue recognition			At a point in time
Mortgage [Member]
Schedule Of Revenue Recognition [Line Items]
Point of revenue recognition			At a point in time
Other Real Estate Owned and Other Assets [Member]
Schedule Of Revenue Recognition [Line Items]
Point of revenue recognition			At a point in time and over time