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Net Income Per Common Share - Average Exercise Prices of Options Excluded from Computation of Diluted Net Income Per Common Share (Detail) (USD $)
3 Months Ended
Mar. 31, 2015
Mar. 31, 2014
Schedule Of Antidilutive Securities Excluded From Computation Of Earnings Per Share [Abstract]    
Shares 128,667us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount 65,000us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount
Average Exercise Price $ 57.68banf_AverageExercisePricesOfOptionsExcludedFromComputationOfDilutedNetIncomePerCommonShare $ 54.01banf_AverageExercisePricesOfOptionsExcludedFromComputationOfDilutedNetIncomePerCommonShare