Parent Directory| Name | Size | Last Modified |
|---|---|---|
 0000860413-22-000191-index-headers.html | 2022-08-05 14:26:15 | |
| 0000860413-22-000191-index.html | 2022-08-05 14:26:15 | |
| 0000860413-22-000191.txt | 2022-08-05 14:26:15 | |
 0000860413-22-000191-xbrl.zip | 685945 | 2022-08-05 14:26:15 |
| fibk-20220630.htm | 5773422 | 2022-08-05 14:26:15 |
| fibk-20220630.xsd | 86342 | 2022-08-05 14:26:15 |
| fibk-20220630xex311.htm | 10317 | 2022-08-05 14:26:15 |
| fibk-20220630xex312.htm | 10467 | 2022-08-05 14:26:15 |
| fibk-20220630xex32.htm | 4171 | 2022-08-05 14:26:15 |
| fibk-20220630xexx101change.htm | 98043 | 2022-08-05 14:26:15 |
| fibk-20220630xexx102change.htm | 97841 | 2022-08-05 14:26:15 |
| fibk-20220630_cal.xml | 189665 | 2022-08-05 14:26:15 |
| fibk-20220630_def.xml | 699185 | 2022-08-05 14:26:15 |
| fibk-20220630_htm.xml | 6946846 | 2022-08-05 14:26:15 |
| fibk-20220630_lab.xml | 1218683 | 2022-08-05 14:26:15 |
| fibk-20220630_pre.xml | 900663 | 2022-08-05 14:26:15 |
| FilingSummary.xml | 49183 | 2022-08-05 14:26:15 |
| Financial_Report.xlsx | 224343 | 2022-08-05 14:26:15 |
| MetaLinks.json | 1147295 | 2022-08-05 14:26:15 |
| R1.htm | 52162 | 2022-08-05 14:26:15 |
| R10.htm | 84480 | 2022-08-05 14:26:15 |
| R11.htm | 44113 | 2022-08-05 14:26:15 |
| R12.htm | 220407 | 2022-08-05 14:26:15 |
| R13.htm | 13245 | 2022-08-05 14:26:15 |
| R14.htm | 1029230 | 2022-08-05 14:26:15 |
| R15.htm | 20838 | 2022-08-05 14:26:15 |
| R16.htm | 162624 | 2022-08-05 14:26:15 |
| R17.htm | 12803 | 2022-08-05 14:26:15 |
| R18.htm | 25214 | 2022-08-05 14:26:15 |
| R19.htm | 88736 | 2022-08-05 14:26:15 |
| R2.htm | 121402 | 2022-08-05 14:26:15 |
| R20.htm | 7436 | 2022-08-05 14:26:15 |
| R21.htm | 24168 | 2022-08-05 14:26:15 |
| R22.htm | 65420 | 2022-08-05 14:26:15 |
| R23.htm | 213246 | 2022-08-05 14:26:15 |
| R24.htm | 27188 | 2022-08-05 14:26:15 |
| R25.htm | 5588 | 2022-08-05 14:26:15 |
| R26.htm | 29292 | 2022-08-05 14:26:15 |
| R27.htm | 17234 | 2022-08-05 14:26:15 |
| R28.htm | 75782 | 2022-08-05 14:26:15 |
| R29.htm | 46561 | 2022-08-05 14:26:15 |
| R3.htm | 29044 | 2022-08-05 14:26:15 |
| R30.htm | 218666 | 2022-08-05 14:26:15 |
| R31.htm | 10277 | 2022-08-05 14:26:15 |
| R32.htm | 1025450 | 2022-08-05 14:26:15 |
| R33.htm | 19975 | 2022-08-05 14:26:15 |
| R34.htm | 143014 | 2022-08-05 14:26:15 |
| R35.htm | 24051 | 2022-08-05 14:26:15 |
| R36.htm | 84504 | 2022-08-05 14:26:15 |
| R37.htm | 21940 | 2022-08-05 14:26:15 |
| R38.htm | 67023 | 2022-08-05 14:26:15 |
| R39.htm | 201373 | 2022-08-05 14:26:15 |
| R4.htm | 129149 | 2022-08-05 14:26:15 |
| R40.htm | 49584 | 2022-08-05 14:26:15 |
| R41.htm | 65282 | 2022-08-05 14:26:15 |
| R42.htm | 19155 | 2022-08-05 14:26:15 |
| R43.htm | 34043 | 2022-08-05 14:26:15 |
| R44.htm | 14523 | 2022-08-05 14:26:15 |
| R45.htm | 21531 | 2022-08-05 14:26:15 |
| R46.htm | 15432 | 2022-08-05 14:26:15 |
| R47.htm | 7972 | 2022-08-05 14:26:15 |
| R48.htm | 26781 | 2022-08-05 14:26:15 |
| R49.htm | 25684 | 2022-08-05 14:26:15 |
| R5.htm | 45876 | 2022-08-05 14:26:15 |
| R50.htm | 83261 | 2022-08-05 14:26:15 |
| R51.htm | 50819 | 2022-08-05 14:26:15 |
| R52.htm | 54904 | 2022-08-05 14:26:15 |
| R53.htm | 8608 | 2022-08-05 14:26:15 |
| R54.htm | 65037 | 2022-08-05 14:26:15 |
| R55.htm | 59911 | 2022-08-05 14:26:15 |
| R56.htm | 21865 | 2022-08-05 14:26:15 |
| R57.htm | 190478 | 2022-08-05 14:26:15 |
| R58.htm | 121859 | 2022-08-05 14:26:15 |
| R59.htm | 105391 | 2022-08-05 14:26:15 |
| R6.htm | 59994 | 2022-08-05 14:26:15 |
| R60.htm | 31110 | 2022-08-05 14:26:15 |
| R61.htm | 58805 | 2022-08-05 14:26:15 |
| R62.htm | 188115 | 2022-08-05 14:26:15 |
| R63.htm | 52488 | 2022-08-05 14:26:15 |
| R64.htm | 386330 | 2022-08-05 14:26:15 |
| R65.htm | 19050 | 2022-08-05 14:26:15 |
| R66.htm | 14908 | 2022-08-05 14:26:15 |
| R67.htm | 26793 | 2022-08-05 14:26:15 |
| R68.htm | 113681 | 2022-08-05 14:26:15 |
| R69.htm | 56511 | 2022-08-05 14:26:15 |
| R7.htm | 21103 | 2022-08-05 14:26:15 |
| R70.htm | 44162 | 2022-08-05 14:26:15 |
| R71.htm | 43564 | 2022-08-05 14:26:15 |
| R72.htm | 94668 | 2022-08-05 14:26:15 |
| R73.htm | 17342 | 2022-08-05 14:26:15 |
| R74.htm | 19018 | 2022-08-05 14:26:15 |
| R75.htm | 53584 | 2022-08-05 14:26:15 |
| R76.htm | 80093 | 2022-08-05 14:26:15 |
| R77.htm | 170727 | 2022-08-05 14:26:15 |
| R78.htm | 53263 | 2022-08-05 14:26:15 |
| R79.htm | 87311 | 2022-08-05 14:26:15 |
| R8.htm | 181306 | 2022-08-05 14:26:15 |
| R80.htm | 6797 | 2022-08-05 14:26:15 |
| R9.htm | 7198 | 2022-08-05 14:26:15 |
| report.css | 2767 | 2022-08-05 14:26:15 |
| Show.js | 1085 | 2022-08-05 14:26:15 |