Revenue Recognition - Summary of Revenue Recognition (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Schedule Of Revenue Recognition [Line Items]
Total net securities brokerage revenue	$ 1,524	$ 1,679
Debit card sponsorship income	646	708
Electronic banking fees	4,365	4,254
Mortgage banking income	4,264	1,276
Net gain on other real estate owned and other assets	175	169
Total Service Charges on Deposits [Member]
Schedule Of Revenue Recognition [Line Items]
Total trust fees/Total service charges on deposits	4,894	6,617
Trust Account fees [Member]
Schedule Of Revenue Recognition [Line Items]
Total trust fees/Total service charges on deposits	$ 5,313	4,857
Point of revenue recognition	Over time
WesMark Fees [Member]
Schedule Of Revenue Recognition [Line Items]
Total trust fees/Total service charges on deposits	$ 2,318	2,095
Point of revenue recognition	Over time
Total Trust Fees [Member]
Schedule Of Revenue Recognition [Line Items]
Total trust fees/Total service charges on deposits	$ 7,631	6,952
Commercial Banking Fees [Member]
Schedule Of Revenue Recognition [Line Items]
Total trust fees/Total service charges on deposits	$ 564	585
Point of revenue recognition	Over time
Personal Service Charges [Member]
Schedule Of Revenue Recognition [Line Items]
Total trust fees/Total service charges on deposits	$ 4,330	6,032
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	$ 917	1,038
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	$ 76	159
Point of revenue recognition	At a point in time
Managed Money [Member]
Schedule Of Revenue Recognition [Line Items]
Total net securities brokerage revenue	$ 283	235
Point of revenue recognition	Over time
Trail Commissions [Member]
Schedule Of Revenue Recognition [Line Items]
Total net securities brokerage revenue	$ 248	247
Point of revenue recognition	Over time
Payment Processing Fees [Member]
Schedule Of Revenue Recognition [Line Items]
Payment Processing Fees	$ 713	$ 680
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