XML 92 R79.htm IDEA: XBRL DOCUMENT
v3.22.4

Loans Held for Investment - Schedule of Loans by Segment (Details) - USD ($) $ in Millions | 12 Months Ended |  |
--- | --- | --- | ---
Dec. 31, 2020 | Dec. 31, 2022 | Dec. 31, 2021
Loans and Leases Receivable |  |  |
Loans and Leases Receivable, Deferred Income |  | $ (15.6) | $ (12.3)
Loans and Leases Receivable, Net of Deferred Income |  | 18,099.2 | 9,331.7
Accounts Receivable, Allowance for Credit Loss | $ (144.3) | (220.1) | (122.3)
Accounts Receivable, Allowance for Credit Loss, Beginning Balance | 73.0 |  |
Financing Receivable, Allowance for Credit Losses, Effect of Change in Method | 30.0 |  |
Commercial Real Estate Portfolio Segment [Member] |  |  |
Loans and Leases Receivable |  |  |
Accounts Receivable, Allowance for Credit Loss | (54.8) | (74.6) | (43.9)
Accounts Receivable, Allowance for Credit Loss, Beginning Balance | 19.5 |  |
Financing Receivable, Allowance for Credit Losses, Effect of Change in Method | 15.3 |  |
Loans and Leases Receivable, Collateral for Secured Borrowings |  | 8,528.6 | 3,971.5
Residential Real Estate Construction Financing Receivable [Member] |  |  |
Loans and Leases Receivable |  |  |
Accounts Receivable, Allowance for Credit Loss | (1.6) | (3.6) | (2.4)
Accounts Receivable, Allowance for Credit Loss, Beginning Balance | 1.5 |  |
Financing Receivable, Allowance for Credit Losses, Effect of Change in Method | 0.9 |  |
Loans and Leases Receivable, Collateral for Secured Borrowings |  | 516.2 | 262.0
Commercial Real Estate Construction [Member] |  |  |
Loans and Leases Receivable |  |  |
Accounts Receivable, Allowance for Credit Loss | (7.3) | (31.2) | (6.0)
Accounts Receivable, Allowance for Credit Loss, Beginning Balance | 2.7 |  |
Financing Receivable, Allowance for Credit Losses, Effect of Change in Method | 1.3 |  |
Loans and Leases Receivable, Collateral for Secured Borrowings |  | 1,042.0 | 498.0
Real Estate Construction Financing Receivable [Member] |  |  |
Loans and Leases Receivable |  |  |
Loans and Leases Receivable, Collateral for Secured Borrowings |  | 1,944.4 | 1,007.8
Residential Mortgage [Member] |  |  |
Loans and Leases Receivable |  |  |
Loans and Leases Receivable, Collateral for Secured Borrowings |  | 2,188.3 | 1,538.2
Agricultural Real Estate Financing Receivable [Member] |  |  |
Loans and Leases Receivable |  |  |
Accounts Receivable, Allowance for Credit Loss | (2.7) | (5.9) | (1.9)
Accounts Receivable, Allowance for Credit Loss, Beginning Balance | 0.5 |  |
Financing Receivable, Allowance for Credit Losses, Effect of Change in Method | 1.8 |  |
Loans and Leases Receivable, Collateral for Secured Borrowings |  | 794.9 | 213.9
Real Estate Financing Receivable [Member] |  |  |
Loans and Leases Receivable |  |  |
Accounts Receivable, Allowance for Credit Loss | (80.5) | (138.7) | (69.3)
Accounts Receivable, Allowance for Credit Loss, Beginning Balance | 28.9 |  |
Financing Receivable, Allowance for Credit Losses, Effect of Change in Method | 28.5 |  |
Loans and Leases Receivable, Collateral for Secured Borrowings |  | 13,456.2 | 6,731.4
Indirect consumer |  |  |
Loans and Leases Receivable |  |  |
Accounts Receivable, Allowance for Credit Loss | (16.7) | (15.3) | (14.3)
Accounts Receivable, Allowance for Credit Loss, Beginning Balance | 4.5 |  |
Financing Receivable, Allowance for Credit Losses, Effect of Change in Method | 8.8 |  |
Loans and Leases Receivable, Collateral for Secured Borrowings |  | 829.7 | 737.6
Other consumer |  |  |
Loans and Leases Receivable |  |  |
Accounts Receivable, Allowance for Credit Loss | (4.6) | (5.2) | (4.6)
Accounts Receivable, Allowance for Credit Loss, Beginning Balance | 2.9 |  |
Financing Receivable, Allowance for Credit Losses, Effect of Change in Method | 3.0 |  |
Loans and Leases Receivable, Collateral for Secured Borrowings |  | 152.9 | 129.2
Credit card consumer |  |  |
Loans and Leases Receivable |  |  |
Accounts Receivable, Allowance for Credit Loss | (2.6) | (2.8) | (2.2)
Accounts Receivable, Allowance for Credit Loss, Beginning Balance | 2.5 |  |
Financing Receivable, Allowance for Credit Losses, Effect of Change in Method | 0.3 |  |
Loans and Leases Receivable, Collateral for Secured Borrowings |  | 75.9 | 64.9
Total consumer loans |  |  |
Loans and Leases Receivable |  |  |
Accounts Receivable, Allowance for Credit Loss | (23.9) | (23.3) | (21.1)
Accounts Receivable, Allowance for Credit Loss, Beginning Balance | 9.9 |  |
Financing Receivable, Allowance for Credit Losses, Effect of Change in Method | 12.1 |  |
Loans and Leases Receivable, Collateral for Secured Borrowings |  | 1,058.5 | 931.7
Commercial Portfolio Segment [Member] |  |  |
Loans and Leases Receivable |  |  |
Accounts Receivable, Allowance for Credit Loss | (39.2) | (54.9) | (31.6)
Accounts Receivable, Allowance for Credit Loss, Beginning Balance | 32.6 |  |
Financing Receivable, Allowance for Credit Losses, Effect of Change in Method | 10.0 |  |
Loans and Leases Receivable, Collateral for Secured Borrowings |  | 2,882.6 | 1,475.5
Agricultural Financing Receivable [Member] |  |  |
Loans and Leases Receivable |  |  |
Accounts Receivable, Allowance for Credit Loss | (0.7) | (3.2) | (0.3)
Accounts Receivable, Allowance for Credit Loss, Beginning Balance | 1.6 |  |
Financing Receivable, Allowance for Credit Losses, Effect of Change in Method | 0.6 |  |
Loans and Leases Receivable, Collateral for Secured Borrowings |  | 708.3 | 203.9
Other, including overdrafts |  |  |
Loans and Leases Receivable |  |  |
Loans and Leases Receivable, Collateral for Secured Borrowings |  | 9.2 | 1.5
Loans held for investment |  |  |
Loans and Leases Receivable |  |  |
Loans and Leases Receivable, Collateral for Secured Borrowings |  | 18,114.8 | 9,344.0
Non Owner Occupied Loans |  |  |
Loans and Leases Receivable |  |  |
Accounts Receivable, Allowance for Credit Loss | (25.5) | (27.2) | (17.3)
Accounts Receivable, Allowance for Credit Loss, Beginning Balance | 8.8 |  |
Financing Receivable, Allowance for Credit Losses, Effect of Change in Method | 4.9 |  |
Commercial Real Estate Owner Occupied |  |  |
Loans and Leases Receivable |  |  |
Accounts Receivable, Allowance for Credit Loss | (18.3) | (19.5) | (13.3)
Accounts Receivable, Allowance for Credit Loss, Beginning Balance | 10.0 |  |
Financing Receivable, Allowance for Credit Losses, Effect of Change in Method | 3.5 |  |
Commercial Real Estate Multifamily |  |  |
Loans and Leases Receivable |  |  |
Accounts Receivable, Allowance for Credit Loss | (11.0) | (27.9) | (13.3)
Accounts Receivable, Allowance for Credit Loss, Beginning Balance | 0.7 |  |
Financing Receivable, Allowance for Credit Losses, Effect of Change in Method | 6.9 |  |
Land Acquisition And Development Construction Financing Receivable [Member] |  |  |
Loans and Leases Receivable |  |  |
Accounts Receivable, Allowance for Credit Loss | (1.3) | (1.3) | (0.5)
Accounts Receivable, Allowance for Credit Loss, Beginning Balance | 1.9 |  |
Financing Receivable, Allowance for Credit Losses, Effect of Change in Method | 0.1 |  |
Loans and Leases Receivable, Collateral for Secured Borrowings |  | 386.2 | 247.8
Construction Loans |  |  |
Loans and Leases Receivable |  |  |
Accounts Receivable, Allowance for Credit Loss | (10.2) | (36.1) | (8.9)
Accounts Receivable, Allowance for Credit Loss, Beginning Balance | 6.1 |  |
Financing Receivable, Allowance for Credit Losses, Effect of Change in Method | 0.3 |  |
Residential Real Estate 1-4 Family |  |  |
Loans and Leases Receivable |  |  |
Accounts Receivable, Allowance for Credit Loss | (11.4) | (20.5) | (13.4)
Accounts Receivable, Allowance for Credit Loss, Beginning Balance | 1.8 |  |
Financing Receivable, Allowance for Credit Losses, Effect of Change in Method | (10.6) |  |
Home Equity Loan |  |  |
Loans and Leases Receivable |  |  |
Accounts Receivable, Allowance for Credit Loss | (1.4) |  | (1.2)
Accounts Receivable, Allowance for Credit Loss, Beginning Balance | 1.0 |  |
Financing Receivable, Allowance for Credit Losses, Effect of Change in Method | (0.5) |  |
Residential Real Estate |  |  |
Loans and Leases Receivable |  |  |
Accounts Receivable, Allowance for Credit Loss | (12.8) | (22.1) | (14.6)
Accounts Receivable, Allowance for Credit Loss, Beginning Balance | 2.8 |  |
Financing Receivable, Allowance for Credit Losses, Effect of Change in Method | (11.1) |  |
Commercial and Floor Plans |  |  |
Loans and Leases Receivable |  |  |
Accounts Receivable, Allowance for Credit Loss | (34.2) | (49.0) | (27.1)
Accounts Receivable, Allowance for Credit Loss, Beginning Balance | 25.5 |  |
Financing Receivable, Allowance for Credit Losses, Effect of Change in Method | 5.1 |  |
Commercial Purpose Secured by 1-4 Family |  |  |
Loans and Leases Receivable |  |  |
Accounts Receivable, Allowance for Credit Loss | (4.7) | (5.7) | (4.4)
Accounts Receivable, Allowance for Credit Loss, Beginning Balance | 5.9 |  |
Financing Receivable, Allowance for Credit Losses, Effect of Change in Method | 3.8 |  |
Commercial Borrower |  |  |
Loans and Leases Receivable |  |  |
Accounts Receivable, Allowance for Credit Loss | (0.3) | $ (0.2) | $ (0.1)
Accounts Receivable, Allowance for Credit Loss, Beginning Balance | 1.2 |  |
Financing Receivable, Allowance for Credit Losses, Effect of Change in Method | $ 1.1 |  |

X
- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + Details
Name: | us-gaap_AccountsNotesAndLoansReceivableLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Amount of allowance for credit loss on accounts receivable. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 326 -SubTopic 20 -Section 50 -Paragraph 13 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=124255953&loc=SL82919249-210447 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section 50 -Paragraph 4 -URI http://asc.fasb.org/extlink&oid=123577603&loc=d3e5074-111524 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 326 -SubTopic 20 -Section 50 -Paragraph 13 -Subparagraph (f) -URI http://asc.fasb.org/extlink&oid=124255953&loc=SL82919249-210447 Reference 4: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 326 -SubTopic 20 -Section 45 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=124255206&loc=SL82895884-210446 + Details
Name: | us-gaap_AllowanceForDoubtfulAccountsReceivable
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition The effect of a change in method or methods for calculating the allowance for credit losses on the current period provision. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section 50 -Paragraph 11B -Subparagraph (d) -URI http://asc.fasb.org/extlink&oid=123577603&loc=SL6953423-111524 + Details
Name: | us-gaap_FinancingReceivableAllowanceForCreditLossesEffectOfChangeInMethod
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Amount excluding accrued interest, before allowance for credit loss, of financing receivable. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 326 -SubTopic 20 -Section 50 -Paragraph 5 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=124255953&loc=SL82919230-210447 Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 326 -SubTopic 20 -Section 45 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=124255206&loc=SL82895884-210446 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 326 -SubTopic 20 -Section 50 -Paragraph 3B -URI http://asc.fasb.org/extlink&oid=124255953&loc=SL120267963-210447 + Details
Name: | us-gaap_FinancingReceivableExcludingAccruedInterestBeforeAllowanceForCreditLoss
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Amount of deferred interest and fee income, unamortized costs incurred to originate loans and leases, unamortized loan commitments and loan syndication fees, and premiums over or discounts from face amounts of acquired loans. Excludes amounts for loans and leases covered under loss sharing agreements. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-03.7) -URI http://asc.fasb.org/extlink&oid=120398452&loc=d3e534808-122878 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 840 -SubTopic 30 -Section 50 -Paragraph 4 -Subparagraph (a)(4) -URI http://asc.fasb.org/extlink&oid=123392090&loc=d3e45377-112738 Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section 50 -Paragraph 4 -URI http://asc.fasb.org/extlink&oid=123577603&loc=d3e5074-111524 Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 20 -Section 50 -Paragraph 3 -URI http://asc.fasb.org/extlink&oid=84159169&loc=d3e10152-111534 + Details
Name: | us-gaap_LoansAndLeasesReceivableDeferredIncome
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Amount before allowance and after deduction of deferred interest and fees, unamortized costs and premiums and discounts from face amounts, of loans and leases held in portfolio, including but not limited to, commercial and consumer loans. Excludes loans and leases covered under loss sharing agreements. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section 45 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=124259787&loc=d3e4428-111522 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section 50 -Paragraph 4 -URI http://asc.fasb.org/extlink&oid=123577603&loc=d3e5074-111524 + Details
Name: | us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Details
Name: | us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=us-gaap_CommercialRealEstatePortfolioSegmentMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=fibk_ResidentialRealEstateConstructionFinancingReceivableMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=fibk_CommercialRealEstateConstructionMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=fibk_RealEstateConstructionFinancingReceivableMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=us-gaap_ResidentialMortgageMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=fibk_AgriculturalRealEstateFinancingReceivableMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=fibk_RealEstateFinancingReceivableMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=fibk_ConsumerIndirectFinancingReceivableMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=us-gaap_ConsumerLoanMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=us-gaap_CreditCardReceivablesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=us-gaap_ConsumerPortfolioSegmentMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=us-gaap_CommercialPortfolioSegmentMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=fibk_AgriculturalFinancingReceivableMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=fibk_OtherFinancingReceivableIncludingOverdraftsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=fibk_LoansAndLeasesHeldForInvestmentMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=fibk_CommercialRealEstateNonOwnerOccupiedLoansMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=fibk_CommercialRealEstateOwnerOccupiedMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=fibk_CommercialRealEstateMultifamilyMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=fibk_LandAcquisitionAndDevelopmentConstructionFinancingReceivableMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=us-gaap_ConstructionLoansMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=fibk_ResidentialRealEstate14FamilyMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=us-gaap_HomeEquityLoanMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=us-gaap_ResidentialRealEstateMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=fibk_CommercialAndFloorPlansMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=fibk_CommercialPurposeSecuredBy14FamilyMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=us-gaap_CommercialBorrowerMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |