Loans - Schedule of Loans Renegotiated in Troubled Debt Restructurings (Details) (USD $) In Thousands, unless otherwise specified
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12 Months Ended |
Dec. 31, 2014
notes
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Dec. 31, 2013
notes
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Dec. 31, 2012
notes
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Loans and Leases Receivable, Troubled Debt Restructuring |
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Financing Receivables, Impaired, Troubled Debt Restructuring, Write-down |
$ 0us-gaap_FinancingReceivablesImpairedTroubledDebtRestructuringWriteDown |
$ 0us-gaap_FinancingReceivablesImpairedTroubledDebtRestructuringWriteDown |
$ 0us-gaap_FinancingReceivablesImpairedTroubledDebtRestructuringWriteDown |
Loans renegotiated in troubled debt restructurings |
44,227us-gaap_FinancingReceivableModificationsRecordedInvestment |
59,792us-gaap_FinancingReceivableModificationsRecordedInvestment |
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Loans renegotiated in troubled debt restructurings, non-accrual loans |
23,275fibk_FinancingReceivableModificationsRecordedInvestmentNonAccrual |
38,011fibk_FinancingReceivableModificationsRecordedInvestmentNonAccrual |
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Loans tenegotiated in troubled debt restructurings, accrual loans |
20,952fibk_FinancingReceivableModificationsRecordedInvestmentAccrualMethod |
21,781fibk_FinancingReceivableModificationsRecordedInvestmentAccrualMethod |
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Financing receivable, modifications, subsequent default, number of contracts, during period |
20us-gaap_FinancingReceivableModificationsNumberOfContracts2 |
43us-gaap_FinancingReceivableModificationsNumberOfContracts2 |
38us-gaap_FinancingReceivableModificationsNumberOfContracts2 |
Financing Receivable, Modifications, Pre-Modification Recorded Investment |
7,190us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2 |
28,403us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2 |
22,760us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2 |
Interest only period |
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Loans and Leases Receivable, Troubled Debt Restructuring |
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Financing Receivable, Modifications, Pre-Modification Recorded Investment |
5,229us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2 / fibk_FinancingReceivableTroubledDebtRestructuringConcessionTypeAxis = fibk_InterestOnlyPeriodConcessionMember |
1,684us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2 / fibk_FinancingReceivableTroubledDebtRestructuringConcessionTypeAxis = fibk_InterestOnlyPeriodConcessionMember |
955us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2 / fibk_FinancingReceivableTroubledDebtRestructuringConcessionTypeAxis = fibk_InterestOnlyPeriodConcessionMember |
Extension of terms or maturity |
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Loans and Leases Receivable, Troubled Debt Restructuring |
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Financing Receivable, Modifications, Pre-Modification Recorded Investment |
785us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2 / fibk_FinancingReceivableTroubledDebtRestructuringConcessionTypeAxis = fibk_ExtensionOfTermsOrMaturityConcessionMember |
9,980us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2 / fibk_FinancingReceivableTroubledDebtRestructuringConcessionTypeAxis = fibk_ExtensionOfTermsOrMaturityConcessionMember |
2,704us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2 / fibk_FinancingReceivableTroubledDebtRestructuringConcessionTypeAxis = fibk_ExtensionOfTermsOrMaturityConcessionMember |
Interest rate adjustment |
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Loans and Leases Receivable, Troubled Debt Restructuring |
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Financing Receivable, Modifications, Pre-Modification Recorded Investment |
84us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2 / fibk_FinancingReceivableTroubledDebtRestructuringConcessionTypeAxis = fibk_InterestRateAdjustmentConcessionMember |
14,263us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2 / fibk_FinancingReceivableTroubledDebtRestructuringConcessionTypeAxis = fibk_InterestRateAdjustmentConcessionMember |
6,494us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2 / fibk_FinancingReceivableTroubledDebtRestructuringConcessionTypeAxis = fibk_InterestRateAdjustmentConcessionMember |
Other |
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Loans and Leases Receivable, Troubled Debt Restructuring |
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Financing Receivable, Modifications, Pre-Modification Recorded Investment |
1,092us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2 / fibk_FinancingReceivableTroubledDebtRestructuringConcessionTypeAxis = fibk_OtherConcessionMember |
2,476us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2 / fibk_FinancingReceivableTroubledDebtRestructuringConcessionTypeAxis = fibk_OtherConcessionMember |
12,607us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2 / fibk_FinancingReceivableTroubledDebtRestructuringConcessionTypeAxis = fibk_OtherConcessionMember |
Commercial real estate |
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Loans and Leases Receivable, Troubled Debt Restructuring |
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Financing receivable, modifications, subsequent default, number of contracts, during period |
13us-gaap_FinancingReceivableModificationsNumberOfContracts2 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialRealEstateOtherReceivableMember |
19us-gaap_FinancingReceivableModificationsNumberOfContracts2 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialRealEstateOtherReceivableMember |
16us-gaap_FinancingReceivableModificationsNumberOfContracts2 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialRealEstateOtherReceivableMember |
Financing Receivable, Modifications, Pre-Modification Recorded Investment |
6,556us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialRealEstateOtherReceivableMember |
15,651us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialRealEstateOtherReceivableMember |
14,074us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialRealEstateOtherReceivableMember |
Commercial real estate | Interest only period |
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Loans and Leases Receivable, Troubled Debt Restructuring |
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Financing Receivable, Modifications, Pre-Modification Recorded Investment |
4,753us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialRealEstateOtherReceivableMember / fibk_FinancingReceivableTroubledDebtRestructuringConcessionTypeAxis = fibk_InterestOnlyPeriodConcessionMember |
543us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialRealEstateOtherReceivableMember / fibk_FinancingReceivableTroubledDebtRestructuringConcessionTypeAxis = fibk_InterestOnlyPeriodConcessionMember |
0us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialRealEstateOtherReceivableMember / fibk_FinancingReceivableTroubledDebtRestructuringConcessionTypeAxis = fibk_InterestOnlyPeriodConcessionMember |
Commercial real estate | Extension of terms or maturity |
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Loans and Leases Receivable, Troubled Debt Restructuring |
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Financing Receivable, Modifications, Pre-Modification Recorded Investment |
672us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialRealEstateOtherReceivableMember / fibk_FinancingReceivableTroubledDebtRestructuringConcessionTypeAxis = fibk_ExtensionOfTermsOrMaturityConcessionMember |
1,378us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialRealEstateOtherReceivableMember / fibk_FinancingReceivableTroubledDebtRestructuringConcessionTypeAxis = fibk_ExtensionOfTermsOrMaturityConcessionMember |
959us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialRealEstateOtherReceivableMember / fibk_FinancingReceivableTroubledDebtRestructuringConcessionTypeAxis = fibk_ExtensionOfTermsOrMaturityConcessionMember |
Commercial real estate | Interest rate adjustment |
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Loans and Leases Receivable, Troubled Debt Restructuring |
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Financing Receivable, Modifications, Pre-Modification Recorded Investment |
84us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialRealEstateOtherReceivableMember / fibk_FinancingReceivableTroubledDebtRestructuringConcessionTypeAxis = fibk_InterestRateAdjustmentConcessionMember |
11,420us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialRealEstateOtherReceivableMember / fibk_FinancingReceivableTroubledDebtRestructuringConcessionTypeAxis = fibk_InterestRateAdjustmentConcessionMember |
4,504us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialRealEstateOtherReceivableMember / fibk_FinancingReceivableTroubledDebtRestructuringConcessionTypeAxis = fibk_InterestRateAdjustmentConcessionMember |
Commercial real estate | Other |
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Loans and Leases Receivable, Troubled Debt Restructuring |
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Financing Receivable, Modifications, Pre-Modification Recorded Investment |
1,047us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialRealEstateOtherReceivableMember / fibk_FinancingReceivableTroubledDebtRestructuringConcessionTypeAxis = fibk_OtherConcessionMember |
2,310us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialRealEstateOtherReceivableMember / fibk_FinancingReceivableTroubledDebtRestructuringConcessionTypeAxis = fibk_OtherConcessionMember |
8,611us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialRealEstateOtherReceivableMember / fibk_FinancingReceivableTroubledDebtRestructuringConcessionTypeAxis = fibk_OtherConcessionMember |
Commercial construction real estate |
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Loans and Leases Receivable, Troubled Debt Restructuring |
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Financing receivable, modifications, subsequent default, number of contracts, during period |
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1us-gaap_FinancingReceivableModificationsNumberOfContracts2 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialRealEstateConstructionFinancingReceivableMember |
Financing Receivable, Modifications, Pre-Modification Recorded Investment |
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3,155us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialRealEstateConstructionFinancingReceivableMember |
Commercial construction real estate | Interest only period |
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Loans and Leases Receivable, Troubled Debt Restructuring |
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Financing Receivable, Modifications, Pre-Modification Recorded Investment |
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0us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialRealEstateConstructionFinancingReceivableMember / fibk_FinancingReceivableTroubledDebtRestructuringConcessionTypeAxis = fibk_InterestOnlyPeriodConcessionMember |
Commercial construction real estate | Extension of terms or maturity |
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Loans and Leases Receivable, Troubled Debt Restructuring |
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Financing Receivable, Modifications, Pre-Modification Recorded Investment |
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0us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialRealEstateConstructionFinancingReceivableMember / fibk_FinancingReceivableTroubledDebtRestructuringConcessionTypeAxis = fibk_ExtensionOfTermsOrMaturityConcessionMember |
Commercial construction real estate | Interest rate adjustment |
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Loans and Leases Receivable, Troubled Debt Restructuring |
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Financing Receivable, Modifications, Pre-Modification Recorded Investment |
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0us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialRealEstateConstructionFinancingReceivableMember / fibk_FinancingReceivableTroubledDebtRestructuringConcessionTypeAxis = fibk_InterestRateAdjustmentConcessionMember |
Commercial construction real estate | Other |
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Loans and Leases Receivable, Troubled Debt Restructuring |
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Financing Receivable, Modifications, Pre-Modification Recorded Investment |
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3,155us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialRealEstateConstructionFinancingReceivableMember / fibk_FinancingReceivableTroubledDebtRestructuringConcessionTypeAxis = fibk_OtherConcessionMember |
Land acquisition & development construction real estate |
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Loans and Leases Receivable, Troubled Debt Restructuring |
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Financing receivable, modifications, subsequent default, number of contracts, during period |
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8us-gaap_FinancingReceivableModificationsNumberOfContracts2 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fibk_LandAcquisitionDevelopmentConstructionFinancingReceivableMember |
5us-gaap_FinancingReceivableModificationsNumberOfContracts2 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fibk_LandAcquisitionDevelopmentConstructionFinancingReceivableMember |
Financing Receivable, Modifications, Pre-Modification Recorded Investment |
|
9,788us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fibk_LandAcquisitionDevelopmentConstructionFinancingReceivableMember |
3,380us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fibk_LandAcquisitionDevelopmentConstructionFinancingReceivableMember |
Land acquisition & development construction real estate | Interest only period |
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Loans and Leases Receivable, Troubled Debt Restructuring |
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Financing Receivable, Modifications, Pre-Modification Recorded Investment |
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528us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fibk_LandAcquisitionDevelopmentConstructionFinancingReceivableMember / fibk_FinancingReceivableTroubledDebtRestructuringConcessionTypeAxis = fibk_InterestOnlyPeriodConcessionMember |
0us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fibk_LandAcquisitionDevelopmentConstructionFinancingReceivableMember / fibk_FinancingReceivableTroubledDebtRestructuringConcessionTypeAxis = fibk_InterestOnlyPeriodConcessionMember |
Land acquisition & development construction real estate | Extension of terms or maturity |
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Loans and Leases Receivable, Troubled Debt Restructuring |
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Financing Receivable, Modifications, Pre-Modification Recorded Investment |
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7,308us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fibk_LandAcquisitionDevelopmentConstructionFinancingReceivableMember / fibk_FinancingReceivableTroubledDebtRestructuringConcessionTypeAxis = fibk_ExtensionOfTermsOrMaturityConcessionMember |
1,000us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fibk_LandAcquisitionDevelopmentConstructionFinancingReceivableMember / fibk_FinancingReceivableTroubledDebtRestructuringConcessionTypeAxis = fibk_ExtensionOfTermsOrMaturityConcessionMember |
Land acquisition & development construction real estate | Interest rate adjustment |
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Loans and Leases Receivable, Troubled Debt Restructuring |
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Financing Receivable, Modifications, Pre-Modification Recorded Investment |
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1,952us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fibk_LandAcquisitionDevelopmentConstructionFinancingReceivableMember / fibk_FinancingReceivableTroubledDebtRestructuringConcessionTypeAxis = fibk_InterestRateAdjustmentConcessionMember |
1,757us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fibk_LandAcquisitionDevelopmentConstructionFinancingReceivableMember / fibk_FinancingReceivableTroubledDebtRestructuringConcessionTypeAxis = fibk_InterestRateAdjustmentConcessionMember |
Land acquisition & development construction real estate | Other |
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Loans and Leases Receivable, Troubled Debt Restructuring |
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Financing Receivable, Modifications, Pre-Modification Recorded Investment |
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0us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fibk_LandAcquisitionDevelopmentConstructionFinancingReceivableMember / fibk_FinancingReceivableTroubledDebtRestructuringConcessionTypeAxis = fibk_OtherConcessionMember |
623us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fibk_LandAcquisitionDevelopmentConstructionFinancingReceivableMember / fibk_FinancingReceivableTroubledDebtRestructuringConcessionTypeAxis = fibk_OtherConcessionMember |
Residential construction real estate |
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Loans and Leases Receivable, Troubled Debt Restructuring |
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Financing receivable, modifications, subsequent default, number of contracts, during period |
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3us-gaap_FinancingReceivableModificationsNumberOfContracts2 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fibk_ResidentialConstructionRealEstateMember |
2us-gaap_FinancingReceivableModificationsNumberOfContracts2 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fibk_ResidentialConstructionRealEstateMember |
Financing Receivable, Modifications, Pre-Modification Recorded Investment |
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819us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fibk_ResidentialConstructionRealEstateMember |
513us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fibk_ResidentialConstructionRealEstateMember |
Residential construction real estate | Interest only period |
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Loans and Leases Receivable, Troubled Debt Restructuring |
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Financing Receivable, Modifications, Pre-Modification Recorded Investment |
|
0us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fibk_ResidentialConstructionRealEstateMember / fibk_FinancingReceivableTroubledDebtRestructuringConcessionTypeAxis = fibk_InterestOnlyPeriodConcessionMember |
0us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fibk_ResidentialConstructionRealEstateMember / fibk_FinancingReceivableTroubledDebtRestructuringConcessionTypeAxis = fibk_InterestOnlyPeriodConcessionMember |
Residential construction real estate | Extension of terms or maturity |
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Loans and Leases Receivable, Troubled Debt Restructuring |
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Financing Receivable, Modifications, Pre-Modification Recorded Investment |
|
408us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fibk_ResidentialConstructionRealEstateMember / fibk_FinancingReceivableTroubledDebtRestructuringConcessionTypeAxis = fibk_ExtensionOfTermsOrMaturityConcessionMember |
280us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fibk_ResidentialConstructionRealEstateMember / fibk_FinancingReceivableTroubledDebtRestructuringConcessionTypeAxis = fibk_ExtensionOfTermsOrMaturityConcessionMember |
Residential construction real estate | Interest rate adjustment |
|
|
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Loans and Leases Receivable, Troubled Debt Restructuring |
|
|
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Financing Receivable, Modifications, Pre-Modification Recorded Investment |
|
411us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fibk_ResidentialConstructionRealEstateMember / fibk_FinancingReceivableTroubledDebtRestructuringConcessionTypeAxis = fibk_InterestRateAdjustmentConcessionMember |
233us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fibk_ResidentialConstructionRealEstateMember / fibk_FinancingReceivableTroubledDebtRestructuringConcessionTypeAxis = fibk_InterestRateAdjustmentConcessionMember |
Residential construction real estate | Other |
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Loans and Leases Receivable, Troubled Debt Restructuring |
|
|
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Financing Receivable, Modifications, Pre-Modification Recorded Investment |
|
0us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fibk_ResidentialConstructionRealEstateMember / fibk_FinancingReceivableTroubledDebtRestructuringConcessionTypeAxis = fibk_OtherConcessionMember |
0us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fibk_ResidentialConstructionRealEstateMember / fibk_FinancingReceivableTroubledDebtRestructuringConcessionTypeAxis = fibk_OtherConcessionMember |
Total construction loans |
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Loans and Leases Receivable, Troubled Debt Restructuring |
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Financing receivable, modifications, subsequent default, number of contracts, during period |
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11us-gaap_FinancingReceivableModificationsNumberOfContracts2 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fibk_RealEstateConstructionFinancingReceivableMember |
8us-gaap_FinancingReceivableModificationsNumberOfContracts2 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fibk_RealEstateConstructionFinancingReceivableMember |
Financing Receivable, Modifications, Pre-Modification Recorded Investment |
|
10,607us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fibk_RealEstateConstructionFinancingReceivableMember |
7,048us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fibk_RealEstateConstructionFinancingReceivableMember |
Total construction loans | Interest only period |
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Loans and Leases Receivable, Troubled Debt Restructuring |
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|
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Financing Receivable, Modifications, Pre-Modification Recorded Investment |
|
528us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fibk_RealEstateConstructionFinancingReceivableMember / fibk_FinancingReceivableTroubledDebtRestructuringConcessionTypeAxis = fibk_InterestOnlyPeriodConcessionMember |
0us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fibk_RealEstateConstructionFinancingReceivableMember / fibk_FinancingReceivableTroubledDebtRestructuringConcessionTypeAxis = fibk_InterestOnlyPeriodConcessionMember |
Total construction loans | Extension of terms or maturity |
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Loans and Leases Receivable, Troubled Debt Restructuring |
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|
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Financing Receivable, Modifications, Pre-Modification Recorded Investment |
|
7,716us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fibk_RealEstateConstructionFinancingReceivableMember / fibk_FinancingReceivableTroubledDebtRestructuringConcessionTypeAxis = fibk_ExtensionOfTermsOrMaturityConcessionMember |
1,280us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fibk_RealEstateConstructionFinancingReceivableMember / fibk_FinancingReceivableTroubledDebtRestructuringConcessionTypeAxis = fibk_ExtensionOfTermsOrMaturityConcessionMember |
Total construction loans | Interest rate adjustment |
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Loans and Leases Receivable, Troubled Debt Restructuring |
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Financing Receivable, Modifications, Pre-Modification Recorded Investment |
|
2,363us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fibk_RealEstateConstructionFinancingReceivableMember / fibk_FinancingReceivableTroubledDebtRestructuringConcessionTypeAxis = fibk_InterestRateAdjustmentConcessionMember |
1,990us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fibk_RealEstateConstructionFinancingReceivableMember / fibk_FinancingReceivableTroubledDebtRestructuringConcessionTypeAxis = fibk_InterestRateAdjustmentConcessionMember |
Total construction loans | Other |
|
|
|
Loans and Leases Receivable, Troubled Debt Restructuring |
|
|
|
Financing Receivable, Modifications, Pre-Modification Recorded Investment |
|
0us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fibk_RealEstateConstructionFinancingReceivableMember / fibk_FinancingReceivableTroubledDebtRestructuringConcessionTypeAxis = fibk_OtherConcessionMember |
3,778us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fibk_RealEstateConstructionFinancingReceivableMember / fibk_FinancingReceivableTroubledDebtRestructuringConcessionTypeAxis = fibk_OtherConcessionMember |
Residential real estate |
|
|
|
Loans and Leases Receivable, Troubled Debt Restructuring |
|
|
|
Financing receivable, modifications, subsequent default, number of contracts, during period |
1us-gaap_FinancingReceivableModificationsNumberOfContracts2 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ResidentialMortgageMember |
5us-gaap_FinancingReceivableModificationsNumberOfContracts2 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ResidentialMortgageMember |
2us-gaap_FinancingReceivableModificationsNumberOfContracts2 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ResidentialMortgageMember |
Financing Receivable, Modifications, Pre-Modification Recorded Investment, Restructured During Period |
15fibk_FinancingReceivableModificationsPreModificationRecordedInvestmentRestructuredDuringPeriod / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ResidentialMortgageMember |
|
|
Financing Receivable, Modifications, Pre-Modification Recorded Investment |
|
787us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ResidentialMortgageMember |
593us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ResidentialMortgageMember |
Residential real estate | Interest only period |
|
|
|
Loans and Leases Receivable, Troubled Debt Restructuring |
|
|
|
Financing Receivable, Modifications, Pre-Modification Recorded Investment, Restructured During Period |
0fibk_FinancingReceivableModificationsPreModificationRecordedInvestmentRestructuredDuringPeriod / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ResidentialMortgageMember / fibk_FinancingReceivableTroubledDebtRestructuringConcessionTypeAxis = fibk_InterestOnlyPeriodConcessionMember |
|
|
Financing Receivable, Modifications, Pre-Modification Recorded Investment |
|
0us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ResidentialMortgageMember / fibk_FinancingReceivableTroubledDebtRestructuringConcessionTypeAxis = fibk_InterestOnlyPeriodConcessionMember |
568us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ResidentialMortgageMember / fibk_FinancingReceivableTroubledDebtRestructuringConcessionTypeAxis = fibk_InterestOnlyPeriodConcessionMember |
Residential real estate | Extension of terms or maturity |
|
|
|
Loans and Leases Receivable, Troubled Debt Restructuring |
|
|
|
Financing Receivable, Modifications, Pre-Modification Recorded Investment, Restructured During Period |
0fibk_FinancingReceivableModificationsPreModificationRecordedInvestmentRestructuredDuringPeriod / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ResidentialMortgageMember / fibk_FinancingReceivableTroubledDebtRestructuringConcessionTypeAxis = fibk_ExtensionOfTermsOrMaturityConcessionMember |
|
|
Financing Receivable, Modifications, Pre-Modification Recorded Investment |
|
708us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ResidentialMortgageMember / fibk_FinancingReceivableTroubledDebtRestructuringConcessionTypeAxis = fibk_ExtensionOfTermsOrMaturityConcessionMember |
25us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ResidentialMortgageMember / fibk_FinancingReceivableTroubledDebtRestructuringConcessionTypeAxis = fibk_ExtensionOfTermsOrMaturityConcessionMember |
Residential real estate | Interest rate adjustment |
|
|
|
Loans and Leases Receivable, Troubled Debt Restructuring |
|
|
|
Financing Receivable, Modifications, Pre-Modification Recorded Investment, Restructured During Period |
0fibk_FinancingReceivableModificationsPreModificationRecordedInvestmentRestructuredDuringPeriod / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ResidentialMortgageMember / fibk_FinancingReceivableTroubledDebtRestructuringConcessionTypeAxis = fibk_InterestRateAdjustmentConcessionMember |
|
|
Financing Receivable, Modifications, Pre-Modification Recorded Investment |
|
0us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ResidentialMortgageMember / fibk_FinancingReceivableTroubledDebtRestructuringConcessionTypeAxis = fibk_InterestRateAdjustmentConcessionMember |
0us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ResidentialMortgageMember / fibk_FinancingReceivableTroubledDebtRestructuringConcessionTypeAxis = fibk_InterestRateAdjustmentConcessionMember |
Residential real estate | Other |
|
|
|
Loans and Leases Receivable, Troubled Debt Restructuring |
|
|
|
Financing Receivable, Modifications, Pre-Modification Recorded Investment, Restructured During Period |
15fibk_FinancingReceivableModificationsPreModificationRecordedInvestmentRestructuredDuringPeriod / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ResidentialMortgageMember / fibk_FinancingReceivableTroubledDebtRestructuringConcessionTypeAxis = fibk_OtherConcessionMember |
|
|
Financing Receivable, Modifications, Pre-Modification Recorded Investment |
|
79us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ResidentialMortgageMember / fibk_FinancingReceivableTroubledDebtRestructuringConcessionTypeAxis = fibk_OtherConcessionMember |
0us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ResidentialMortgageMember / fibk_FinancingReceivableTroubledDebtRestructuringConcessionTypeAxis = fibk_OtherConcessionMember |
Agricultural real estate |
|
|
|
Loans and Leases Receivable, Troubled Debt Restructuring |
|
|
|
Financing receivable, modifications, subsequent default, number of contracts, during period |
|
1us-gaap_FinancingReceivableModificationsNumberOfContracts2 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fibk_AgriculturalRealEstateFinancingReceivableMember |
1us-gaap_FinancingReceivableModificationsNumberOfContracts2 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fibk_AgriculturalRealEstateFinancingReceivableMember |
Financing Receivable, Modifications, Pre-Modification Recorded Investment |
|
188us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fibk_AgriculturalRealEstateFinancingReceivableMember |
154us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fibk_AgriculturalRealEstateFinancingReceivableMember |
Agricultural real estate | Interest only period |
|
|
|
Loans and Leases Receivable, Troubled Debt Restructuring |
|
|
|
Financing Receivable, Modifications, Pre-Modification Recorded Investment |
|
0us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fibk_AgriculturalRealEstateFinancingReceivableMember / fibk_FinancingReceivableTroubledDebtRestructuringConcessionTypeAxis = fibk_InterestOnlyPeriodConcessionMember |
0us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fibk_AgriculturalRealEstateFinancingReceivableMember / fibk_FinancingReceivableTroubledDebtRestructuringConcessionTypeAxis = fibk_InterestOnlyPeriodConcessionMember |
Agricultural real estate | Extension of terms or maturity |
|
|
|
Loans and Leases Receivable, Troubled Debt Restructuring |
|
|
|
Financing Receivable, Modifications, Pre-Modification Recorded Investment |
|
0us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fibk_AgriculturalRealEstateFinancingReceivableMember / fibk_FinancingReceivableTroubledDebtRestructuringConcessionTypeAxis = fibk_ExtensionOfTermsOrMaturityConcessionMember |
154us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fibk_AgriculturalRealEstateFinancingReceivableMember / fibk_FinancingReceivableTroubledDebtRestructuringConcessionTypeAxis = fibk_ExtensionOfTermsOrMaturityConcessionMember |
Agricultural real estate | Interest rate adjustment |
|
|
|
Loans and Leases Receivable, Troubled Debt Restructuring |
|
|
|
Financing Receivable, Modifications, Pre-Modification Recorded Investment |
|
188us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fibk_AgriculturalRealEstateFinancingReceivableMember / fibk_FinancingReceivableTroubledDebtRestructuringConcessionTypeAxis = fibk_InterestRateAdjustmentConcessionMember |
0us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fibk_AgriculturalRealEstateFinancingReceivableMember / fibk_FinancingReceivableTroubledDebtRestructuringConcessionTypeAxis = fibk_InterestRateAdjustmentConcessionMember |
Agricultural real estate | Other |
|
|
|
Loans and Leases Receivable, Troubled Debt Restructuring |
|
|
|
Financing Receivable, Modifications, Pre-Modification Recorded Investment |
|
0us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fibk_AgriculturalRealEstateFinancingReceivableMember / fibk_FinancingReceivableTroubledDebtRestructuringConcessionTypeAxis = fibk_OtherConcessionMember |
0us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fibk_AgriculturalRealEstateFinancingReceivableMember / fibk_FinancingReceivableTroubledDebtRestructuringConcessionTypeAxis = fibk_OtherConcessionMember |
Total real estate loans |
|
|
|
Loans and Leases Receivable, Troubled Debt Restructuring |
|
|
|
Financing receivable, modifications, subsequent default, number of contracts, during period |
14us-gaap_FinancingReceivableModificationsNumberOfContracts2 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fibk_RealEstateFinancingReceivableMember |
36us-gaap_FinancingReceivableModificationsNumberOfContracts2 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fibk_RealEstateFinancingReceivableMember |
27us-gaap_FinancingReceivableModificationsNumberOfContracts2 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fibk_RealEstateFinancingReceivableMember |
Financing Receivable, Modifications, Pre-Modification Recorded Investment |
6,571us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fibk_RealEstateFinancingReceivableMember |
27,233us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fibk_RealEstateFinancingReceivableMember |
21,869us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fibk_RealEstateFinancingReceivableMember |
Total real estate loans | Interest only period |
|
|
|
Loans and Leases Receivable, Troubled Debt Restructuring |
|
|
|
Financing Receivable, Modifications, Pre-Modification Recorded Investment |
4,753us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fibk_RealEstateFinancingReceivableMember / fibk_FinancingReceivableTroubledDebtRestructuringConcessionTypeAxis = fibk_InterestOnlyPeriodConcessionMember |
1,071us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fibk_RealEstateFinancingReceivableMember / fibk_FinancingReceivableTroubledDebtRestructuringConcessionTypeAxis = fibk_InterestOnlyPeriodConcessionMember |
568us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fibk_RealEstateFinancingReceivableMember / fibk_FinancingReceivableTroubledDebtRestructuringConcessionTypeAxis = fibk_InterestOnlyPeriodConcessionMember |
Total real estate loans | Extension of terms or maturity |
|
|
|
Loans and Leases Receivable, Troubled Debt Restructuring |
|
|
|
Financing Receivable, Modifications, Pre-Modification Recorded Investment |
672us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fibk_RealEstateFinancingReceivableMember / fibk_FinancingReceivableTroubledDebtRestructuringConcessionTypeAxis = fibk_ExtensionOfTermsOrMaturityConcessionMember |
9,802us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fibk_RealEstateFinancingReceivableMember / fibk_FinancingReceivableTroubledDebtRestructuringConcessionTypeAxis = fibk_ExtensionOfTermsOrMaturityConcessionMember |
2,418us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fibk_RealEstateFinancingReceivableMember / fibk_FinancingReceivableTroubledDebtRestructuringConcessionTypeAxis = fibk_ExtensionOfTermsOrMaturityConcessionMember |
Total real estate loans | Interest rate adjustment |
|
|
|
Loans and Leases Receivable, Troubled Debt Restructuring |
|
|
|
Financing Receivable, Modifications, Pre-Modification Recorded Investment |
84us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fibk_RealEstateFinancingReceivableMember / fibk_FinancingReceivableTroubledDebtRestructuringConcessionTypeAxis = fibk_InterestRateAdjustmentConcessionMember |
13,971us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fibk_RealEstateFinancingReceivableMember / fibk_FinancingReceivableTroubledDebtRestructuringConcessionTypeAxis = fibk_InterestRateAdjustmentConcessionMember |
6,494us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fibk_RealEstateFinancingReceivableMember / fibk_FinancingReceivableTroubledDebtRestructuringConcessionTypeAxis = fibk_InterestRateAdjustmentConcessionMember |
Total real estate loans | Other |
|
|
|
Loans and Leases Receivable, Troubled Debt Restructuring |
|
|
|
Financing Receivable, Modifications, Pre-Modification Recorded Investment |
1,062us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fibk_RealEstateFinancingReceivableMember / fibk_FinancingReceivableTroubledDebtRestructuringConcessionTypeAxis = fibk_OtherConcessionMember |
2,389us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fibk_RealEstateFinancingReceivableMember / fibk_FinancingReceivableTroubledDebtRestructuringConcessionTypeAxis = fibk_OtherConcessionMember |
12,389us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fibk_RealEstateFinancingReceivableMember / fibk_FinancingReceivableTroubledDebtRestructuringConcessionTypeAxis = fibk_OtherConcessionMember |
Total consumer loans |
|
|
|
Loans and Leases Receivable, Troubled Debt Restructuring |
|
|
|
Financing receivable, modifications, subsequent default, number of contracts, during period |
1us-gaap_FinancingReceivableModificationsNumberOfContracts2 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fibk_ConsumerFinancingReceivableMember |
1us-gaap_FinancingReceivableModificationsNumberOfContracts2 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fibk_ConsumerFinancingReceivableMember |
1us-gaap_FinancingReceivableModificationsNumberOfContracts2 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fibk_ConsumerFinancingReceivableMember |
Financing Receivable, Modifications, Pre-Modification Recorded Investment |
113us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fibk_ConsumerFinancingReceivableMember |
27us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fibk_ConsumerFinancingReceivableMember |
69us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fibk_ConsumerFinancingReceivableMember |
Total consumer loans | Interest only period |
|
|
|
Loans and Leases Receivable, Troubled Debt Restructuring |
|
|
|
Financing Receivable, Modifications, Pre-Modification Recorded Investment |
0us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fibk_ConsumerFinancingReceivableMember / fibk_FinancingReceivableTroubledDebtRestructuringConcessionTypeAxis = fibk_InterestOnlyPeriodConcessionMember |
0us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fibk_ConsumerFinancingReceivableMember / fibk_FinancingReceivableTroubledDebtRestructuringConcessionTypeAxis = fibk_InterestOnlyPeriodConcessionMember |
0us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fibk_ConsumerFinancingReceivableMember / fibk_FinancingReceivableTroubledDebtRestructuringConcessionTypeAxis = fibk_InterestOnlyPeriodConcessionMember |
Total consumer loans | Extension of terms or maturity |
|
|
|
Loans and Leases Receivable, Troubled Debt Restructuring |
|
|
|
Financing Receivable, Modifications, Pre-Modification Recorded Investment |
113us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fibk_ConsumerFinancingReceivableMember / fibk_FinancingReceivableTroubledDebtRestructuringConcessionTypeAxis = fibk_ExtensionOfTermsOrMaturityConcessionMember |
0us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fibk_ConsumerFinancingReceivableMember / fibk_FinancingReceivableTroubledDebtRestructuringConcessionTypeAxis = fibk_ExtensionOfTermsOrMaturityConcessionMember |
69us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fibk_ConsumerFinancingReceivableMember / fibk_FinancingReceivableTroubledDebtRestructuringConcessionTypeAxis = fibk_ExtensionOfTermsOrMaturityConcessionMember |
Total consumer loans | Interest rate adjustment |
|
|
|
Loans and Leases Receivable, Troubled Debt Restructuring |
|
|
|
Financing Receivable, Modifications, Pre-Modification Recorded Investment |
0us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fibk_ConsumerFinancingReceivableMember / fibk_FinancingReceivableTroubledDebtRestructuringConcessionTypeAxis = fibk_InterestRateAdjustmentConcessionMember |
27us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fibk_ConsumerFinancingReceivableMember / fibk_FinancingReceivableTroubledDebtRestructuringConcessionTypeAxis = fibk_InterestRateAdjustmentConcessionMember |
0us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fibk_ConsumerFinancingReceivableMember / fibk_FinancingReceivableTroubledDebtRestructuringConcessionTypeAxis = fibk_InterestRateAdjustmentConcessionMember |
Total consumer loans | Other |
|
|
|
Loans and Leases Receivable, Troubled Debt Restructuring |
|
|
|
Financing Receivable, Modifications, Pre-Modification Recorded Investment |
0us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fibk_ConsumerFinancingReceivableMember / fibk_FinancingReceivableTroubledDebtRestructuringConcessionTypeAxis = fibk_OtherConcessionMember |
0us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fibk_ConsumerFinancingReceivableMember / fibk_FinancingReceivableTroubledDebtRestructuringConcessionTypeAxis = fibk_OtherConcessionMember |
0us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fibk_ConsumerFinancingReceivableMember / fibk_FinancingReceivableTroubledDebtRestructuringConcessionTypeAxis = fibk_OtherConcessionMember |
Commercial |
|
|
|
Loans and Leases Receivable, Troubled Debt Restructuring |
|
|
|
Financing receivable, modifications, subsequent default, number of contracts, during period |
5us-gaap_FinancingReceivableModificationsNumberOfContracts2 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fibk_CommercialFinancingReceivableMember |
6us-gaap_FinancingReceivableModificationsNumberOfContracts2 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fibk_CommercialFinancingReceivableMember |
10us-gaap_FinancingReceivableModificationsNumberOfContracts2 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fibk_CommercialFinancingReceivableMember |
Financing Receivable, Modifications, Pre-Modification Recorded Investment |
506us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fibk_CommercialFinancingReceivableMember |
1,143us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fibk_CommercialFinancingReceivableMember |
822us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fibk_CommercialFinancingReceivableMember |
Commercial | Interest only period |
|
|
|
Loans and Leases Receivable, Troubled Debt Restructuring |
|
|
|
Financing Receivable, Modifications, Pre-Modification Recorded Investment |
476us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fibk_CommercialFinancingReceivableMember / fibk_FinancingReceivableTroubledDebtRestructuringConcessionTypeAxis = fibk_InterestOnlyPeriodConcessionMember |
613us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fibk_CommercialFinancingReceivableMember / fibk_FinancingReceivableTroubledDebtRestructuringConcessionTypeAxis = fibk_InterestOnlyPeriodConcessionMember |
387us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fibk_CommercialFinancingReceivableMember / fibk_FinancingReceivableTroubledDebtRestructuringConcessionTypeAxis = fibk_InterestOnlyPeriodConcessionMember |
Commercial | Extension of terms or maturity |
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Loans and Leases Receivable, Troubled Debt Restructuring |
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Financing Receivable, Modifications, Pre-Modification Recorded Investment |
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217us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fibk_CommercialFinancingReceivableMember / fibk_FinancingReceivableTroubledDebtRestructuringConcessionTypeAxis = fibk_ExtensionOfTermsOrMaturityConcessionMember |
Commercial | Interest rate adjustment |
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Loans and Leases Receivable, Troubled Debt Restructuring |
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Financing Receivable, Modifications, Pre-Modification Recorded Investment |
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0us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fibk_CommercialFinancingReceivableMember / fibk_FinancingReceivableTroubledDebtRestructuringConcessionTypeAxis = fibk_InterestRateAdjustmentConcessionMember |
Commercial | Other |
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Loans and Leases Receivable, Troubled Debt Restructuring |
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Financing Receivable, Modifications, Pre-Modification Recorded Investment |
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$ 87us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fibk_CommercialFinancingReceivableMember / fibk_FinancingReceivableTroubledDebtRestructuringConcessionTypeAxis = fibk_OtherConcessionMember |
$ 218us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fibk_CommercialFinancingReceivableMember / fibk_FinancingReceivableTroubledDebtRestructuringConcessionTypeAxis = fibk_OtherConcessionMember |