Dividends from Subsidiaries	12 Months Ended
Dec. 31, 2023
Text Block [Abstract]
Dividends from Subsidiaries	15. DIVIDENDS FROM SUBSIDIARIES: At December 31, 2023, $387,325,000 was available for the declaration of dividends by the Company’s subsidiaries without the prior approval of regulatory agencies.

Amount available for the declaration of dividends by the Company's subsidiaries without the prior approval of regulatory agencies.

No definition available.

Name:	ffin_DividendsFromSubsidiariesDisclosureTextBlock
Namespace Prefix:	ffin_
Data Type:	dtr-types:textBlockItemType
Balance Type:	na
Period Type:	duration