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Income Taxes - Additional Information (Detail) (Minimum [Member])
Dec. 31, 2014
Minimum [Member]
  
Income Taxes [Line Items]  
Tax position measured if more-likely-than-not threshold is exceeded, percentage 50.00%ffin_PercentageOfCumulativeTaxPosition
/ us-gaap_RangeAxis
= us-gaap_MinimumMember