Fair Value Disclosures - Other Real Estate Owned (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended
Mar. 31, 2015	Mar. 31, 2014
Fair Value Disclosures [Abstract]
Carrying value of other real estate owned prior to remeasurement	$ 10
Write-downs included in gain (loss) on sale of other real estate owned	(10)
Fair value	$ 0ffin_OtherRealEstateOwnedFairValue	$ 0ffin_OtherRealEstateOwnedFairValue

Write downs included in gain loss on sale of other real estate owned.

No definition available.

Name:	ffin_WriteDownsIncludedInGainLossOnSaleOfOtherRealEstateOwned
Namespace Prefix:	ffin_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration