Significant Accounting Policies Newly Adopted and Pending Accounting Pronouncements (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
Mar. 31, 2018	Dec. 31, 2017
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Interchange fees related to transaction card processing revenue	$ 9.5
Increase of reported right of use assets and liabilities		$ 100.0
Increase of reported right of use assets and liabilities maximum		$ 150.0

Interchange fees related to transaction card processing revenue

No definition available.

Name:	bokf_Interchangefeesrelatedtotransactioncardprocessingrevenue
Namespace Prefix:	bokf_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration