Regulatory Matters - Additional Information (Detail) (USD $)	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012
Regulated Operations [Abstract]
Average reserve balances to be maintained by subsidiary banks	$ 245,566,000	$ 239,755,000
Average reserve balances required by subsidiary banks	438,761,000	89,439,000
Retained net profits available for distribution to United Bankshares, Inc. by its banking subsidiaries as dividends	35,547,000
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	$ 77,648,000