Loans to Officers and Directors - Additional Information (Detail) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016
Receivables [Abstract]
Reduction due to change in reportable loans	$ (101,049)	$ (501,413)

Loans and leases receivable related parties reduction due to change in reportable loans.

No definition available.

Name:	umbf_LoansAndLeasesReceivableRelatedPartiesReductionDueToChangeInReportableLoans
Namespace Prefix:	umbf_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration