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Regulatory Matters - Additional Information (Detail) - USD ($)
12 Months Ended
Dec. 31, 2026
Dec. 31, 2025
Dec. 31, 2024
Regulatory Matters [Line Items]      
Average reserve balances to be maintained by subsidiary banks   $ 2,036,744,000 $ 1,184,007,000
Average reserve balances required by subsidiary banks   $ 0 $ 0
Retained net profits available for distribution to United Bankshares, Inc. by its banking subsidiaries as dividends $ 339,113,000    
Maximum loan to parent company by subsidiaries as percentage it's of capital and surplus   10.00%  
Maximum amount of loan to parent company by subsidiaries   $ 425,053,000