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| 0000860413-26-000038-index.html | 2026-05-07 16:10:09 | |
| 0000860413-26-000038.txt | 2026-05-07 16:10:09 | |
 0000860413-26-000038-xbrl.zip | 351769 | 2026-05-07 16:10:09 |
| fibk-20260331.htm | 3110362 | 2026-05-07 16:10:09 |
| fibk-20260331.xsd | 68222 | 2026-05-07 16:10:09 |
| fibk-20260331xex311.htm | 10055 | 2026-05-07 16:10:09 |
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| fibk-20260331xex32.htm | 4028 | 2026-05-07 16:10:09 |
| fibk-20260331_cal.xml | 124524 | 2026-05-07 16:10:09 |
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| report.css | 2767 | 2026-05-07 16:10:09 |
| Show.js | 1085 | 2026-05-07 16:10:09 |