Stock - Based Compensation - Summary of Accumulated Stock Units (Detail) - $ / shares	Jun. 30, 2018	Dec. 31, 2017
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Accumulated stock units	139,114	138,768
Average price	$ 23.87	$ 22.84

Deferred compensation arrangement with individual accumulated stock units For deferred board fees.

No definition available.

Name:	banf_DeferredCompensationArrangementWithIndividualAccumulatedStockUnitsForDeferredBoardFees
Namespace Prefix:	banf_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant