Dividends from Subsidiaries - Additional Information (Detail) (USD $)	Dec. 31, 2012
Equity [Line Items]
Amount available for the declaration of dividends by subsidiary banks without prior approval of regulatory agencies	$ 59,966,000

Amount Available For Dividend Distribution Without Approval From Regulatory Agencies

No definition available.

Name:	ffin_AmountAvailableForDividendDistributionWithoutApprovalFromRegulatoryAgencies
Namespace Prefix:	ffin_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant