XML 75 R66.htm IDEA: XBRL DOCUMENT
v3.23.2

Loans Held for Investment - Schedule of Recorded Investment in Impaired Loans (Details) - USD ($) $ in Millions | 3 Months Ended | 6 Months Ended |  |  |  |
--- | --- | --- | --- | --- | --- | ---
Jun. 30, 2023 | Jun. 30, 2022 | Jun. 30, 2023 | Jun. 30, 2022 | Mar. 31, 2023 | Dec. 31, 2022 | Mar. 31, 2022 | Dec. 31, 2021
Loans and Leases Receivable Recorded Investment, Impaired [Line Items] |  |  |  |  |  |  |  |
Provision charged to operating expense | $ (11.7) | $ 1.7 | $ (26.9) | $ (59.6) |  |  |  |
Accounts Receivable, Allowance for Credit Loss | 224.6 | 220.4 | 224.6 | 220.4 | $ 226.1 | $ 220.1 | $ 247.2 | $ 122.3
Off-Balance Sheet, Credit Loss, Liability, Credit Loss Expense (Reversal) | 9.9 | (1.7) | 22.1 | 55.6 |  |  |  |
Impaired Financing Receivable, Interest Income, Accrual Method | 0.0 | 0.0 | 0.0 | 0.0 |  |  |  |
Total real estate |  |  |  |  |  |  |  |
Loans and Leases Receivable Recorded Investment, Impaired [Line Items] |  |  |  |  |  |  |  |
Provision charged to operating expense | (20.4) | 11.2 | (33.8) | (27.3) |  |  |  |
Accounts Receivable, Allowance for Credit Loss | 158.7 | 133.7 | 158.7 | 133.7 | 147.5 | 138.7 | 169.6 | 69.3
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss | 13,604.4 |  | 13,604.4 |  |  | 13,456.2 |  |
Commercial |  |  |  |  |  |  |  |
Loans and Leases Receivable Recorded Investment, Impaired [Line Items] |  |  |  |  |  |  |  |
Provision charged to operating expense | 4.5 | (2.4) | 5.3 | (21.5) |  |  |  |
Accounts Receivable, Allowance for Credit Loss | 49.5 | 59.9 | 49.5 | 59.9 | 54.4 | 54.9 | 58.2 | 31.6
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss | 3,002.7 |  | 3,002.7 |  |  | 2,882.6 |  |
Agricultural |  |  |  |  |  |  |  |
Loans and Leases Receivable Recorded Investment, Impaired [Line Items] |  |  |  |  |  |  |  |
Provision charged to operating expense | (0.2) | (6.3) | 0.9 | (5.8) |  |  |  |
Accounts Receivable, Allowance for Credit Loss | 2.7 | 6.5 | 2.7 | 6.5 | $ 2.4 | 3.2 | (1.0) | 0.3
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss | 688.0 |  | 688.0 |  |  | 708.3 |  |
Owner occupied |  |  |  |  |  |  |  |
Loans and Leases Receivable Recorded Investment, Impaired [Line Items] |  |  |  |  |  |  |  |
Provision charged to operating expense |  | (1.4) |  | (6.0) |  |  |  |
Accounts Receivable, Allowance for Credit Loss |  | 26.6 |  | 26.6 |  |  | 25.2 | 13.3
Commercial |  |  |  |  |  |  |  |
Loans and Leases Receivable Recorded Investment, Impaired [Line Items] |  |  |  |  |  |  |  |
Provision charged to operating expense |  | 10.3 |  | (12.4) |  |  |  |
Accounts Receivable, Allowance for Credit Loss |  | 89.5 |  | 89.5 |  |  | 125.0 | 43.9
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss | 8,813.9 |  | 8,813.9 |  |  | 8,528.6 |  |
Residential construction |  |  |  |  |  |  |  |
Loans and Leases Receivable Recorded Investment, Impaired [Line Items] |  |  |  |  |  |  |  |
Provision charged to operating expense |  | (0.1) |  | (1.0) |  |  |  |
Accounts Receivable, Allowance for Credit Loss |  | 3.4 |  | 3.4 |  |  | 3.3 | 2.4
Commercial construction |  |  |  |  |  |  |  |
Loans and Leases Receivable Recorded Investment, Impaired [Line Items] |  |  |  |  |  |  |  |
Provision charged to operating expense |  | (4.7) |  | (8.7) |  |  |  |
Accounts Receivable, Allowance for Credit Loss |  | 14.9 |  | 14.9 |  |  | 10.2 | 6.0
Total construction |  |  |  |  |  |  |  |
Loans and Leases Receivable Recorded Investment, Impaired [Line Items] |  |  |  |  |  |  |  |
Provision charged to operating expense |  | (5.0) |  | (9.1) |  |  |  |
Accounts Receivable, Allowance for Credit Loss |  | 19.1 |  | 19.1 |  |  | 14.0 | 8.9
Residential 1-4 family |  |  |  |  |  |  |  |
Loans and Leases Receivable Recorded Investment, Impaired [Line Items] |  |  |  |  |  |  |  |
Provision charged to operating expense |  | 0.7 |  | (4.5) |  |  |  |
Accounts Receivable, Allowance for Credit Loss |  | 18.2 |  | 18.2 |  |  | 18.7 | 13.4
Residential |  |  |  |  |  |  |  |
Loans and Leases Receivable Recorded Investment, Impaired [Line Items] |  |  |  |  |  |  |  |
Provision charged to operating expense |  | 0.8 |  | (4.5) |  |  |  |
Accounts Receivable, Allowance for Credit Loss |  | 19.7 |  | 19.7 |  |  | 20.1 | 14.6
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss | 2,198.3 |  | 2,198.3 |  |  | 2,188.3 |  |
Agricultural |  |  |  |  |  |  |  |
Loans and Leases Receivable Recorded Investment, Impaired [Line Items] |  |  |  |  |  |  |  |
Provision charged to operating expense |  | 5.1 |  | (1.3) |  |  |  |
Accounts Receivable, Allowance for Credit Loss |  | $ 5.4 |  | $ 5.4 |  |  | $ 10.5 | $ 1.9
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss | 755.7 |  | 755.7 |  |  | 794.9 |  |
Total construction loans |  |  |  |  |  |  |  |
Loans and Leases Receivable Recorded Investment, Impaired [Line Items] |  |  |  |  |  |  |  |
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss | 1,836.5 |  | 1,836.5 |  |  | 1,944.4 |  |
Collateral [Member] |  |  |  |  |  |  |  |
Loans and Leases Receivable Recorded Investment, Impaired [Line Items] |  |  |  |  |  |  |  |
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss | 63.5 |  | 63.5 |  |  | 39.1 |  |
Collateral [Member] | Total real estate |  |  |  |  |  |  |  |
Loans and Leases Receivable Recorded Investment, Impaired [Line Items] |  |  |  |  |  |  |  |
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss | 55.9 |  | 55.9 |  |  | 27.2 |  |
Collateral [Member] | Commercial |  |  |  |  |  |  |  |
Loans and Leases Receivable Recorded Investment, Impaired [Line Items] |  |  |  |  |  |  |  |
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss | 6.9 |  | 6.9 |  |  | 4.6 |  |
Collateral [Member] | Agricultural |  |  |  |  |  |  |  |
Loans and Leases Receivable Recorded Investment, Impaired [Line Items] |  |  |  |  |  |  |  |
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss | 0.7 |  | 0.7 |  |  | 7.3 |  |
Collateral [Member] | Commercial |  |  |  |  |  |  |  |
Loans and Leases Receivable Recorded Investment, Impaired [Line Items] |  |  |  |  |  |  |  |
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss | 33.9 |  | 33.9 |  |  | 17.5 |  |
Collateral [Member] | Residential |  |  |  |  |  |  |  |
Loans and Leases Receivable Recorded Investment, Impaired [Line Items] |  |  |  |  |  |  |  |
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss | 0.5 |  | 0.5 |  |  | 0.5 |  |
Collateral [Member] | Agricultural |  |  |  |  |  |  |  |
Loans and Leases Receivable Recorded Investment, Impaired [Line Items] |  |  |  |  |  |  |  |
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss | 3.7 |  | 3.7 |  |  | 6.0 |  |
Collateral [Member] | Total construction loans |  |  |  |  |  |  |  |
Loans and Leases Receivable Recorded Investment, Impaired [Line Items] |  |  |  |  |  |  |  |
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss | 17.8 |  | 17.8 |  |  | 3.2 |  |
Business Assets [Member] | Collateral [Member] |  |  |  |  |  |  |  |
Loans and Leases Receivable Recorded Investment, Impaired [Line Items] |  |  |  |  |  |  |  |
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss | 3.2 |  | 3.2 |  |  | 7.1 |  |
Business Assets [Member] | Collateral [Member] | Total real estate |  |  |  |  |  |  |  |
Loans and Leases Receivable Recorded Investment, Impaired [Line Items] |  |  |  |  |  |  |  |
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss | 1.6 |  | 1.6 |  |  | 1.9 |  |
Business Assets [Member] | Collateral [Member] | Commercial |  |  |  |  |  |  |  |
Loans and Leases Receivable Recorded Investment, Impaired [Line Items] |  |  |  |  |  |  |  |
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss | 1.4 |  | 1.4 |  |  | 3.1 |  |
Business Assets [Member] | Collateral [Member] | Agricultural |  |  |  |  |  |  |  |
Loans and Leases Receivable Recorded Investment, Impaired [Line Items] |  |  |  |  |  |  |  |
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss | 0.2 |  | 0.2 |  |  | 2.1 |  |
Business Assets [Member] | Collateral [Member] | Commercial |  |  |  |  |  |  |  |
Loans and Leases Receivable Recorded Investment, Impaired [Line Items] |  |  |  |  |  |  |  |
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss | 1.6 |  | 1.6 |  |  | 1.7 |  |
Business Assets [Member] | Collateral [Member] | Residential |  |  |  |  |  |  |  |
Loans and Leases Receivable Recorded Investment, Impaired [Line Items] |  |  |  |  |  |  |  |
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss | 0.0 |  | 0.0 |  |  | 0.0 |  |
Business Assets [Member] | Collateral [Member] | Agricultural |  |  |  |  |  |  |  |
Loans and Leases Receivable Recorded Investment, Impaired [Line Items] |  |  |  |  |  |  |  |
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss | 0.0 |  | 0.0 |  |  | 0.2 |  |
Business Assets [Member] | Collateral [Member] | Total construction loans |  |  |  |  |  |  |  |
Loans and Leases Receivable Recorded Investment, Impaired [Line Items] |  |  |  |  |  |  |  |
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss | 0.0 |  | 0.0 |  |  | 0.0 |  |
Real Property [Member] | Collateral [Member] |  |  |  |  |  |  |  |
Loans and Leases Receivable Recorded Investment, Impaired [Line Items] |  |  |  |  |  |  |  |
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss | 60.3 |  | 60.3 |  |  | 32.0 |  |
Real Property [Member] | Collateral [Member] | Total real estate |  |  |  |  |  |  |  |
Loans and Leases Receivable Recorded Investment, Impaired [Line Items] |  |  |  |  |  |  |  |
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss | 54.3 |  | 54.3 |  |  | 25.3 |  |
Real Property [Member] | Collateral [Member] | Commercial |  |  |  |  |  |  |  |
Loans and Leases Receivable Recorded Investment, Impaired [Line Items] |  |  |  |  |  |  |  |
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss | 5.5 |  | 5.5 |  |  | 1.5 |  |
Real Property [Member] | Collateral [Member] | Agricultural |  |  |  |  |  |  |  |
Loans and Leases Receivable Recorded Investment, Impaired [Line Items] |  |  |  |  |  |  |  |
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss | 0.5 |  | 0.5 |  |  | 5.2 |  |
Real Property [Member] | Collateral [Member] | Commercial |  |  |  |  |  |  |  |
Loans and Leases Receivable Recorded Investment, Impaired [Line Items] |  |  |  |  |  |  |  |
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss | 32.3 |  | 32.3 |  |  | 15.8 |  |
Real Property [Member] | Collateral [Member] | Residential |  |  |  |  |  |  |  |
Loans and Leases Receivable Recorded Investment, Impaired [Line Items] |  |  |  |  |  |  |  |
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss | 0.5 |  | 0.5 |  |  | 0.5 |  |
Real Property [Member] | Collateral [Member] | Agricultural |  |  |  |  |  |  |  |
Loans and Leases Receivable Recorded Investment, Impaired [Line Items] |  |  |  |  |  |  |  |
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss | 3.7 |  | 3.7 |  |  | 5.8 |  |
Real Property [Member] | Collateral [Member] | Total construction loans |  |  |  |  |  |  |  |
Loans and Leases Receivable Recorded Investment, Impaired [Line Items] |  |  |  |  |  |  |  |
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss | $ 17.8 |  | $ 17.8 |  |  | $ 3.2 |  |

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 https://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 https://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 https://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 https://asc.fasb.org/extlink&oid=124255206&loc=SL82895884-210446 Reference 5: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02(4)) -URI https://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682 + Details
Name: | us-gaap_AllowanceForDoubtfulAccountsReceivable
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Amortized cost excluding accrued interest, before allowance for credit loss, of financing receivable. Excludes net investment in lease. + 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 https://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 https://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 https://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 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_FinancingReceivableImpairedLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Amount of interest income recognized that the financing receivables (with related allowance for credit losses and without a related allowance for credit losses) were impaired. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section 50 -Paragraph 15 -Subparagraph (c)(2) -URI https://asc.fasb.org/extlink&oid=123577603&loc=d3e5212-111524 + Details
Name: | us-gaap_ImpairedFinancingReceivableInterestIncomeAccrualMethod
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Amount of expense (reversal of expense) for expected credit loss for off-balance sheet credit exposure. Excludes off-balance sheet credit exposure accounted for as insurance and instrument accounted for under derivatives and hedging. + 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 (b) -URI https://asc.fasb.org/extlink&oid=124255953&loc=SL82919249-210447 + Details
Name: | us-gaap_OffBalanceSheetCreditLossLiabilityCreditLossExpenseReversal
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Amount of expense related to estimated loss from loan and lease transactions. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 28 -Subparagraph (a) -URI https://asc.fasb.org/extlink&oid=126954810&loc=d3e3602-108585 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 220 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-04.11) -URI https://asc.fasb.org/extlink&oid=120399700&loc=SL114874048-224260 Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section 50 -Paragraph 11B -Subparagraph (c)(2) -URI https://asc.fasb.org/extlink&oid=123577603&loc=SL6953423-111524 + Details
Name: | us-gaap_ProvisionForLoanAndLeaseLosses
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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

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=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_ResidentialRealEstateMember
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_RealEstateConstructionFinancingReceivableMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | fibk_LoanDependencyAxis=fibk_CollateralMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_CollateralAxis=fibk_BusinessAssetsPledgedasCollateralMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_CollateralAxis=fibk_RealPropertyPledgedasCollateralMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |