Credit Quality - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended	12 Months Ended
	Jun. 30, 2020	Jun. 30, 2020	Dec. 31, 2019
Minimum days for discontinue of accrual interest on commercial and consumer loan		90 days
Maximum days for discontinue of accrual interest on commercial and consumer loan		120 days
Troubled debt restructuring		$ 77,436	$ 58,369
Restructured loans on nonaccrual status	$ 59,916	$ 59,916	48,387
Minimum number of days required for special mention		30 days
Maximum number of days required for special mention		89 days
OREO	29,947	$ 29,947	15,515
Recorded investment of consumer mortgage loans	1,738	1,738	890
Troubled debt restructurings post modification additional funds recorded investment		$ 124
Description of Credit Risk Exposure		For United’s loans with a corporate credit exposure, United analyzes loans individually to classify the loans as to credit risk. Review and analysis of criticized (special mention-rated loans in the amount of $1,000 or greater) and classified (substandard-rated and worse in the amount of $500 and greater) loans is completed once per quarter. Review of notes with committed exposure of $2,000 or greater is completed at least annually.
Payments under funding commitments	38	$ 111
Loans Modification Explanation		As provided for under the CARES Act, these loan modifications are exempt by law from classification as a TDR as defined by GAAP, from the period beginning March 1, 2020 until the earlier of December 31, 2020 or the date that is 60 days after the date
Payment Deferral [Member] | Minimum [Member]
Loans Repayments Minimum Term		90 days
Loans Repayments Maximum Term		180 days
Financing Receivables, Equal to Greater than 90 Days Past Due [Member]
Restructured loans on nonaccrual status	$ 544	$ 544	$ 902