Parent Directory| Name | Size | Last Modified |
|---|---|---|
 0000860413-19-000117-index-headers.html | 2019-08-07 16:03:14 | |
| 0000860413-19-000117-index.html | 2019-08-07 16:03:14 | |
| 0000860413-19-000117.txt | 2019-08-07 16:03:14 | |
 0000860413-19-000117-xbrl.zip | 458310 | 2019-08-07 16:03:14 |
| fibk-20190630.xsd | 76073 | 2019-08-07 16:03:14 |
| fibk-20190630x10q.htm | 4503360 | 2019-08-07 16:03:14 |
| fibk-20190630x10q_htm.xml | 5341027 | 2019-08-07 16:03:14 |
| fibk-20190630xex311.htm | 12182 | 2019-08-07 16:03:14 |
| fibk-20190630xex312.htm | 12714 | 2019-08-07 16:03:14 |
| fibk-20190630xex32.htm | 4714 | 2019-08-07 16:03:14 |
| fibk-20190630_cal.xml | 211761 | 2019-08-07 16:03:14 |
| fibk-20190630_def.xml | 455813 | 2019-08-07 16:03:14 |
| fibk-20190630_lab.xml | 1159737 | 2019-08-07 16:03:14 |
| fibk-20190630_pre.xml | 676530 | 2019-08-07 16:03:14 |
| FilingSummary.xml | 45742 | 2019-08-07 16:03:14 |
| Financial_Report.xlsx | 128377 | 2019-08-07 16:03:14 |
| MetaLinks.json | 925622 | 2019-08-07 16:03:14 |
| R1.htm | 54552 | 2019-08-07 16:03:14 |
| R10.htm | 190069 | 2019-08-07 16:03:14 |
| R11.htm | 40413 | 2019-08-07 16:03:14 |
| R12.htm | 207591 | 2019-08-07 16:03:14 |
| R13.htm | 460961 | 2019-08-07 16:03:14 |
| R14.htm | 168501 | 2019-08-07 16:03:14 |
| R15.htm | 31094 | 2019-08-07 16:03:14 |
| R16.htm | 153199 | 2019-08-07 16:03:14 |
| R17.htm | 10142 | 2019-08-07 16:03:14 |
| R18.htm | 32537 | 2019-08-07 16:03:14 |
| R19.htm | 117872 | 2019-08-07 16:03:14 |
| R2.htm | 96527 | 2019-08-07 16:03:14 |
| R20.htm | 6950 | 2019-08-07 16:03:14 |
| R21.htm | 7067 | 2019-08-07 16:03:14 |
| R22.htm | 80123 | 2019-08-07 16:03:14 |
| R23.htm | 260686 | 2019-08-07 16:03:14 |
| R24.htm | 22525 | 2019-08-07 16:03:14 |
| R25.htm | 6123 | 2019-08-07 16:03:14 |
| R26.htm | 42158 | 2019-08-07 16:03:14 |
| R27.htm | 200742 | 2019-08-07 16:03:14 |
| R28.htm | 41609 | 2019-08-07 16:03:14 |
| R29.htm | 204566 | 2019-08-07 16:03:14 |
| R3.htm | 12305 | 2019-08-07 16:03:14 |
| R30.htm | 462533 | 2019-08-07 16:03:14 |
| R31.htm | 164400 | 2019-08-07 16:03:14 |
| R32.htm | 27026 | 2019-08-07 16:03:14 |
| R33.htm | 152109 | 2019-08-07 16:03:14 |
| R34.htm | 31019 | 2019-08-07 16:03:14 |
| R35.htm | 113082 | 2019-08-07 16:03:14 |
| R36.htm | 81776 | 2019-08-07 16:03:14 |
| R37.htm | 243887 | 2019-08-07 16:03:14 |
| R38.htm | 71618 | 2019-08-07 16:03:14 |
| R39.htm | 118925 | 2019-08-07 16:03:14 |
| R4.htm | 115089 | 2019-08-07 16:03:14 |
| R40.htm | 19661 | 2019-08-07 16:03:14 |
| R41.htm | 12030 | 2019-08-07 16:03:14 |
| R42.htm | 12222 | 2019-08-07 16:03:14 |
| R43.htm | 15828 | 2019-08-07 16:03:14 |
| R44.htm | 9804 | 2019-08-07 16:03:14 |
| R45.htm | 14201 | 2019-08-07 16:03:14 |
| R46.htm | 18601 | 2019-08-07 16:03:14 |
| R47.htm | 52375 | 2019-08-07 16:03:14 |
| R48.htm | 27020 | 2019-08-07 16:03:14 |
| R49.htm | 58916 | 2019-08-07 16:03:14 |
| R5.htm | 30971 | 2019-08-07 16:03:14 |
| R50.htm | 52047 | 2019-08-07 16:03:14 |
| R51.htm | 139488 | 2019-08-07 16:03:14 |
| R52.htm | 9988 | 2019-08-07 16:03:14 |
| R53.htm | 18584 | 2019-08-07 16:03:14 |
| R54.htm | 17567 | 2019-08-07 16:03:14 |
| R55.htm | 73811 | 2019-08-07 16:03:14 |
| R56.htm | 22865 | 2019-08-07 16:03:14 |
| R57.htm | 100889 | 2019-08-07 16:03:14 |
| R58.htm | 77298 | 2019-08-07 16:03:14 |
| R59.htm | 17270 | 2019-08-07 16:03:14 |
| R6.htm | 59706 | 2019-08-07 16:03:14 |
| R60.htm | 22149 | 2019-08-07 16:03:14 |
| R61.htm | 82533 | 2019-08-07 16:03:14 |
| R62.htm | 9863 | 2019-08-07 16:03:14 |
| R63.htm | 41073 | 2019-08-07 16:03:14 |
| R64.htm | 30203 | 2019-08-07 16:03:14 |
| R65.htm | 84027 | 2019-08-07 16:03:14 |
| R66.htm | 9909 | 2019-08-07 16:03:14 |
| R67.htm | 9622 | 2019-08-07 16:03:14 |
| R68.htm | 64762 | 2019-08-07 16:03:14 |
| R69.htm | 17875 | 2019-08-07 16:03:14 |
| R7.htm | 21857 | 2019-08-07 16:03:14 |
| R70.htm | 186922 | 2019-08-07 16:03:14 |
| R71.htm | 40851 | 2019-08-07 16:03:14 |
| R72.htm | 79943 | 2019-08-07 16:03:14 |
| R73.htm | 8112 | 2019-08-07 16:03:14 |
| R74.htm | 6788 | 2019-08-07 16:03:14 |
| R8.htm | 152879 | 2019-08-07 16:03:14 |
| R9.htm | 13410 | 2019-08-07 16:03:14 |
| report.css | 2767 | 2019-08-07 16:03:14 |
| Show.js | 1085 | 2019-08-07 16:03:14 |