XML 41 R32.htm IDEA: XBRL DOCUMENT
v3.22.2.2

Loans Held for Sale (Tables) | 9 Months Ended
--- | ---
Sep. 30, 2022
Receivables [Abstract] |
Loans Held For Sale (Table) | The following table presents loans held for sale by segment for the dates indicated:
| September 30, 2022 |  | December 31, 2021
Loans Held for Sale: |  |  |
Agricultural | $ | 63.0 |  |  | $ | — |
Commercial construction | 12.4 |  |  | — |
Residential real estate | 18.2 |  |  | 30.1 |
Total loans held for sale | $ | 93.6 |  |  | $ | 30.1 |

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

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