XML 102 R89.htm IDEA: XBRL DOCUMENT
v3.22.4

Other Real Estate Owned (Details) - USD ($) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2022 | Dec. 31, 2021 | Dec. 31, 2020
Repossessed Assets [Abstract] |  |  |
Real Estate Acquired Through Foreclosure, Valuation Adjustments | $ 2.8 | $ 0.0 |
Real Estate Acquired Through Foreclosure [Roll Forward] |  |  |
Balance at beginning of year | 2.0 | 2.5 | $ 8.5
OREO acquired through acquisitions | 15.8 | 0.0 | 0.0
Additions | 0.4 | 0.9 | 3.3
Valuation adjustments | (2.8) | 0.0 | (0.1)
Dispositions | (2.7) | (1.4) | (9.2)
Balance at end of year | 12.7 | 2.0 | 2.5
Write-downs of OREO | (2.8) | $ 0.0 | $ (0.1)
Mortgage Loans in Process of Foreclosure, Amount | 0.0 |  |
Carrying value of foreclosed OREO | $ 0.0 |  |

X
- Definition Foreclosed Residential Real Estate included in Other Real Estate Owned + References No definition available. + Details
Name: | fibk_ForeclosedResidentialRealEstateincludedinOtherRealEstateOwned
Namespace Prefix: | fibk_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Real Estate Acquired Through Foreclosure, Acquired Through Acquisition + References No definition available. + Details
Name: | fibk_RealEstateAcquiredThroughForeclosureAcquiredThroughAcquisition
Namespace Prefix: | fibk_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Real Estate Acquired Through Foreclosure, Additions + References No definition available. + Details
Name: | fibk_RealEstateAcquiredThroughForeclosureAdditions
Namespace Prefix: | fibk_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Real Estate Acquired Through Foreclosure, Disposals + References No definition available. + Details
Name: | fibk_RealEstateAcquiredThroughForeclosureDisposals
Namespace Prefix: | fibk_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Real Estate Acquired Through Foreclosure [Roll Forward] + References No definition available. + Details
Name: | fibk_RealEstateAcquiredThroughForeclosureRollForward
Namespace Prefix: | fibk_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Real Estate Acquired Through Foreclosure, Valuation Adjustments + References No definition available. + Details
Name: | fibk_RealEstateAcquiredThroughForeclosureValuationAdjustments
Namespace Prefix: | fibk_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- References No definition available. + Details
Name: | us-gaap_ForeclosedAssetsAbstract
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition The charge against earnings in the period to reduce the carrying amount of real property to fair value. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 28 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=123570139&loc=d3e3602-108585 Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 360 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=109226691&loc=d3e2921-110230 + Details
Name: | us-gaap_ImpairmentOfRealEstate
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Recorded investment of consumer mortgage loan receivables secured by residential real estate properties for which formal foreclosure proceedings are in process. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section 50 -Paragraph 35 -URI http://asc.fasb.org/extlink&oid=123577603&loc=SL49126937-111524 + Details
Name: | us-gaap_MortgageLoansInProcessOfForeclosureAmount
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Carrying amount as of the balance sheet date of land and buildings obtained through foreclosure proceedings or defeasance in full or partial satisfaction of a debt arrangement. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section 50 -Paragraph 11 -URI http://asc.fasb.org/extlink&oid=123577603&loc=d3e5162-111524 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section 45 -Paragraph 3 -URI http://asc.fasb.org/extlink&oid=124259787&loc=d3e4437-111522 + Details
Name: | us-gaap_RealEstateAcquiredThroughForeclosure
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant