Revenue Recognition - Summary of Revenue Recognition (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Schedule Of Revenue Recognition [Line Items]
Total net securities brokerage revenue	$ 1,829	$ 1,384	$ 3,352	$ 3,063
Debit card sponsorship income		644	646	1,351
Electronic banking fees	5,060	4,066	9,426	8,320
Mortgage banking income	7,830	7,531	12,094	8,807
Net gain (loss) on other real estate owned and other assets	4,014	(66)	4,189	103
Total Service Charges on Deposits [Member]
Schedule Of Revenue Recognition [Line Items]
Total trust fees/Total service charges on deposits	4,876	4,323	9,770	10,940
Trust Account fees [Member]
Schedule Of Revenue Recognition [Line Items]
Total trust fees/Total service charges on deposits	4,710	4,189	$ 10,024	9,046
Point of revenue recognition			Over time
WesMark Fees [Member]
Schedule Of Revenue Recognition [Line Items]
Total trust fees/Total service charges on deposits	2,438	2,013	$ 4,756	4,108
Point of revenue recognition			Over time
Total Trust Fees [Member]
Schedule Of Revenue Recognition [Line Items]
Total trust fees/Total service charges on deposits	7,148	6,202	$ 14,780	13,154
Commercial Banking Fees [Member]
Schedule Of Revenue Recognition [Line Items]
Total trust fees/Total service charges on deposits	601	586	$ 1,165	1,171
Point of revenue recognition			Over time
Personal Service Charges [Member]
Schedule Of Revenue Recognition [Line Items]
Total trust fees/Total service charges on deposits	4,275	3,737	$ 8,605	9,769
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	1,151	845	$ 2,067	1,883
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	57	94	$ 133	253
Point of revenue recognition			At a point in time
Managed Money [Member]
Schedule Of Revenue Recognition [Line Items]
Total net securities brokerage revenue	291	214	$ 574	449
Point of revenue recognition			Over time
Trail Commissions [Member]
Schedule Of Revenue Recognition [Line Items]
Total net securities brokerage revenue	330	131	$ 578	478
Point of revenue recognition			Over time
Payment Processing Fees [Member]
Schedule Of Revenue Recognition [Line Items]
Payment Processing Fees	$ 748	$ 784	$ 1,461	$ 1,464
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