XML 61 R50.htm IDEA: XBRL DOCUMENT
v3.20.1

Loans - Schedule of Loans by Segment (Details) - USD ($) | Mar. 31, 2020 | Mar. 27, 2020 | Jan. 01, 2020 | Dec. 31, 2019 | Mar. 31, 2019 | Dec. 31, 2018
--- | --- | --- | --- | --- | --- | ---
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |  |  |
Net deferred loan fees and costs | $ (6,400,000) |  |  | $ (5,500,000) |  |
Loans held for investment | 8,918,000,000.0 |  |  | 8,930,700,000 |  |
Mortgage loans held for sale | 94,400,000 |  |  | 100,900,000 |  |
Total loans, net of deferred fees and costs | 9,012,400,000 | $ 1,000,000,000.0 |  | 9,031,600,000 |  |
Allowance for credit losses | (129,100,000) |  | $ (29,000,000.0) | (73,000,000.0) | $ (72,400,000) | $ (73,000,000.0)
Net loans | 8,883,300,000 |  |  | 8,958,600,000 |  |
Commercial real estate |  |  |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |  |  |
Loans held for investment | 3,543,400,000 |  |  | 3,487,800,000 |  |
Allowance for credit losses | (39,500,000) |  |  | (19,500,000) |  |
Land acquisition & development |  |  |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |  |  |
Loans held for investment | 290,500,000 |  |  | 302,100,000 |  |
Total loans, net of deferred fees and costs | 290.5 |  |  |  |  |
Allowance for credit losses | (1,400,000) |  |  | (1,900,000) |  |
Residential |  |  |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |  |  |
Loans held for investment | 228,400,000 |  |  | 244,100,000 |  |
Total loans, net of deferred fees and costs | 228.4 |  |  |  |  |
Allowance for credit losses | (1,100,000) |  |  | (1,500,000) |  |
Commercial |  |  |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |  |  |
Loans held for investment | 459,400,000 |  |  | 431,500,000 |  |
Total loans, net of deferred fees and costs | 459.4 |  |  |  |  |
Allowance for credit losses | (6,100,000) |  |  | (2,700,000) |  |
Total construction loans |  |  |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |  |  |
Loans held for investment | 978,300,000 |  |  | 977,700,000 |  |
Residential |  |  |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |  |  |
Loans held for investment | 1,231,000,000.0 |  |  | 1,246,100,000 |  |
Allowance for credit losses | (14,300,000) |  |  | (2,800,000) |  |
Agricultural |  |  |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |  |  |
Loans held for investment | 224,600,000 |  |  | 226,600,000 |  |
Total loans, net of deferred fees and costs | 224.6 |  |  |  |  |
Allowance for credit losses | (2,600,000) |  |  | (500,000) |  |
Total real estate loans |  |  |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |  |  |
Loans held for investment | 5,977,300,000 |  |  | 5,938,200,000 |  |
Allowance for credit losses | (65,000,000.0) |  |  | (28,900,000) |  |
Indirect consumer |  |  |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |  |  |
Loans held for investment | 774,600,000 |  |  | 784,600,000 |  |
Total loans, net of deferred fees and costs | 774.6 |  |  |  |  |
Allowance for credit losses | (16,700,000) |  |  | (4,500,000) |  |
Direct and advance lines |  |  |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |  |  |
Loans held for investment | 175,000,000.0 |  |  | 179,000,000.0 |  |
Total loans, net of deferred fees and costs | 175.0 |  |  |  |  |
Allowance for credit losses | (5,500,000) |  |  | (2,900,000) |  |
Credit card |  |  |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |  |  |
Loans held for investment | 75,900,000 |  |  | 81,600,000 |  |
Allowance for credit losses | (2,600,000) |  |  | (2,500,000) |  |
Total consumer loans |  |  |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |  |  |
Loans held for investment | 1,025,500,000 |  |  | 1,045,200,000 |  |
Allowance for credit losses | (24,800,000) |  |  | (9,900,000) |  |
Commercial |  |  |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |  |  |
Loans held for investment | 1,660,000,000.0 |  |  | 1,673,700,000 |  |
Allowance for credit losses | (38,200,000) |  |  | (32,600,000) |  |
Agricultural |  |  |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |  |  |
Loans held for investment | 257,900,000 |  |  | 279,100,000 |  |
Allowance for credit losses | (1,100,000) |  |  | (1,600,000) |  |
Other, including overdrafts |  |  |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |  |  |
Loans held for investment | 3,700,000 |  |  | 0 |  |
Mortgage loans originated for sale |  |  |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |  |  |
Mortgage loans held for sale | 94,400,000 |  |  | 100,900,000 |  |
Total loans |  |  |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |  |  |
Total loans, net of deferred fees and costs | $ 9,012,400,000 |  |  | $ 9,031,600,000 |  |

X
- Definition Gross carrying amount of all categories of loans and leases held in the portfolio, excluding loans held for sale. + References No definition available. + Details
Name: | fibk_LoansAndLeasesReceivableHeldForInvestment
Namespace Prefix: | fibk_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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=121599337&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=121611835&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=121599337&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=121599878&loc=SL82895884-210446 + Details
Name: | us-gaap_AllowanceForDoubtfulAccountsReceivable
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
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_FinancingReceivableRecordedInvestmentPastDueLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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=121568338&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=121611835&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 of loans and leases held in portfolio, including but not limited to, commercial and consumer loans. Includes deferred interest and fees, undisbursed portion of loan balance, unamortized costs and premiums and discounts from face amounts. 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=121593590&loc=d3e4428-111522 + Details
Name: | us-gaap_LoansAndLeasesReceivableGrossCarryingAmount
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Amount after allowance and 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 and loans held for sale. + 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=121593590&loc=d3e4428-111522 Reference 2: 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 + Details
Name: | us-gaap_LoansAndLeasesReceivableNetReportedAmount
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Amount, after valuation allowance, of financing receivable held for sale and not part of disposal group. Excludes loan covered under loss sharing agreement and loan classified as investment in debt security. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section 45 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=121593590&loc=d3e4428-111522 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 948 -SubTopic 310 -Section 45 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=120238483&loc=d3e48678-111004 + Details
Name: | us-gaap_LoansReceivableHeldForSaleNetNotPartOfDisposalGroup
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_LandAcquisitionAndDevelopmentConstructionFinancingReceivableMember
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_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_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_MortgageLoansHeldForSaleMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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