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Loans Schedule of Loans Acquired from Business Combinations (Details) (USD $)
In Thousands, unless otherwise specified
Mar. 31, 2015
Mar. 31, 2014
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities [Abstract]    
Outstanding Balance $ 32,445us-gaap_CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesOutstandingBalance $ 0us-gaap_CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesOutstandingBalance
Carrying Amount Net, Accrual Status 23,909fibk_CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesCarryingAmountNetAccrualStatus 0fibk_CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesCarryingAmountNetAccrualStatus
Carrying Amount Net, Non Accrual Status 0fibk_CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesCarryingAmountNetNonAccrualStatus 0fibk_CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesCarryingAmountNetNonAccrualStatus
Total Carrying Value $ 23,909us-gaap_CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesCarryingAmountNet $ 0us-gaap_CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesCarryingAmountNet