XML 40 R28.htm IDEA: XBRL DOCUMENT
v3.24.1.u1

Loans Held for Sale (Tables) | 3 Months Ended
--- | ---
Mar. 31, 2024
Loans Held for Sale [Abstract] |
Loans Held For Sale (Table) | The following table presents loans held for sale by class of receivable for the dates indicated:
| March 31, 2024 |  | December 31, 2023
Loans held for sale: |  |  |
Agricultural, at lower of cost or market | $ | 19.5 |  |  | $ | 19.6 |
Commercial real estate, at lower of cost or market | — |  |  | 27.3 |
Residential mortgage, at fair value | 3.2 |  |  | 0.5 |
Total loans held for sale | $ | 22.7 |  |  | $ | 47.4 |
Non-Residential Loans Held for Sale | The table below presents the non-residential mortgage loans held for sale activity for the 2024 period:
| Agricultural |  |  |  | Commercial Real Estate
Beginning balance | $ | 19.6 |  |  |  |  | $ | 27.3 |
Repayments | (0.1) |  |  |  |  | — |
Loan disposals | — |  |  |  |  | (27.3) |
Ending balance | $ | 19.5 |  |  |  |  | $ | — |

X
- Definition Loans Held For Sale (Table) + References No definition available. + Details
Name: | fibk_LoansHeldForSaleTableTableTextBlock
Namespace Prefix: | fibk_
Data Type: | dtr-types1:textBlockItemType
Balance Type: | na
Period Type: | duration

X
- Definition Loans Held for Sale [Abstract] + References No definition available. + Details
Name: | fibk_LoansHeldforSaleAbstract
Namespace Prefix: | fibk_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Non-Residential Loans Held for Sale + References No definition available. + Details
Name: | fibk_NonResidentialLoansHeldForSaleTableTextBlock
Namespace Prefix: | fibk_
Data Type: | dtr-types1:textBlockItemType
Balance Type: | na
Period Type: | duration