Parent Directory| Name | Size | Last Modified |
|---|---|---|
 0000860413-17-000009-index-headers.html | 2017-03-01 20:09:14 | |
| 0000860413-17-000009-index.html | 2017-03-01 20:09:14 | |
| 0000860413-17-000009.txt | 2017-03-01 20:09:14 | |
 0000860413-17-000009-xbrl.zip | 614085 | 2017-03-01 20:09:14 |
 fibk-201412_chartx24070a03.jpg | 86470 | 2017-03-01 20:09:14 |
| fibk-20161231.xml | 6517204 | 2017-03-01 20:09:14 |
| fibk-20161231.xsd | 126868 | 2017-03-01 20:09:14 |
| fibk-20161231x10k.htm | 4423602 | 2017-03-01 20:09:14 |
| fibk-20161231xex211.htm | 16230 | 2017-03-01 20:09:14 |
| fibk-20161231xex231.htm | 5939 | 2017-03-01 20:09:14 |
| fibk-20161231xex311.htm | 13739 | 2017-03-01 20:09:14 |
| fibk-20161231xex312.htm | 13715 | 2017-03-01 20:09:14 |
| fibk-20161231xex32.htm | 7398 | 2017-03-01 20:09:14 |
| fibk-20161231_cal.xml | 246166 | 2017-03-01 20:09:14 |
| fibk-20161231_def.xml | 763810 | 2017-03-01 20:09:14 |
| fibk-20161231_lab.xml | 1826009 | 2017-03-01 20:09:14 |
| fibk-20161231_pre.xml | 1100775 | 2017-03-01 20:09:14 |
| FilingSummary.xml | 71170 | 2017-03-01 20:09:14 |
| Financial_Report.xlsx | 206249 | 2017-03-01 20:09:14 |
| R1.htm | 29808 | 2017-03-01 20:09:14 |
| R10.htm | 87230 | 2017-03-01 20:09:14 |
| R100.htm | 23389 | 2017-03-01 20:09:14 |
| R101.htm | 52329 | 2017-03-01 20:09:14 |
| R102.htm | 32109 | 2017-03-01 20:09:14 |
| R103.htm | 16764 | 2017-03-01 20:09:14 |
| R104.htm | 25581 | 2017-03-01 20:09:14 |
| R105.htm | 51636 | 2017-03-01 20:09:14 |
| R106.htm | 22610 | 2017-03-01 20:09:14 |
| R107.htm | 50742 | 2017-03-01 20:09:14 |
| R108.htm | 54498 | 2017-03-01 20:09:14 |
| R109.htm | 14264 | 2017-03-01 20:09:14 |
| R11.htm | 231275 | 2017-03-01 20:09:14 |
| R110.htm | 13387 | 2017-03-01 20:09:14 |
| R111.htm | 43416 | 2017-03-01 20:09:14 |
| R112.htm | 40312 | 2017-03-01 20:09:14 |
| R113.htm | 80577 | 2017-03-01 20:09:14 |
| R114.htm | 130056 | 2017-03-01 20:09:14 |
| R115.htm | 31575 | 2017-03-01 20:09:14 |
| R116.htm | 80999 | 2017-03-01 20:09:14 |
| R117.htm | 58856 | 2017-03-01 20:09:14 |
| R118.htm | 13190 | 2017-03-01 20:09:14 |
| R12.htm | 627001 | 2017-03-01 20:09:14 |
| R13.htm | 174233 | 2017-03-01 20:09:14 |
| R14.htm | 18919 | 2017-03-01 20:09:14 |
| R15.htm | 19903 | 2017-03-01 20:09:14 |
| R16.htm | 28161 | 2017-03-01 20:09:14 |
| R17.htm | 66451 | 2017-03-01 20:09:14 |
| R18.htm | 39240 | 2017-03-01 20:09:14 |
| R19.htm | 36524 | 2017-03-01 20:09:14 |
| R2.htm | 102083 | 2017-03-01 20:09:14 |
| R20.htm | 38380 | 2017-03-01 20:09:14 |
| R21.htm | 39257 | 2017-03-01 20:09:14 |
| R22.htm | 17280 | 2017-03-01 20:09:14 |
| R23.htm | 31105 | 2017-03-01 20:09:14 |
| R24.htm | 140637 | 2017-03-01 20:09:14 |
| R25.htm | 36005 | 2017-03-01 20:09:14 |
| R26.htm | 9661 | 2017-03-01 20:09:14 |
| R27.htm | 88211 | 2017-03-01 20:09:14 |
| R28.htm | 62348 | 2017-03-01 20:09:14 |
| R29.htm | 20820 | 2017-03-01 20:09:14 |
| R3.htm | 14820 | 2017-03-01 20:09:14 |
| R30.htm | 64823 | 2017-03-01 20:09:14 |
| R31.htm | 9516 | 2017-03-01 20:09:14 |
| R32.htm | 142710 | 2017-03-01 20:09:14 |
| R33.htm | 301598 | 2017-03-01 20:09:14 |
| R34.htm | 19471 | 2017-03-01 20:09:14 |
| R35.htm | 41742 | 2017-03-01 20:09:14 |
| R36.htm | 7277 | 2017-03-01 20:09:14 |
| R37.htm | 125709 | 2017-03-01 20:09:14 |
| R38.htm | 76909 | 2017-03-01 20:09:14 |
| R39.htm | 219794 | 2017-03-01 20:09:14 |
| R4.htm | 107230 | 2017-03-01 20:09:14 |
| R40.htm | 615904 | 2017-03-01 20:09:14 |
| R41.htm | 170617 | 2017-03-01 20:09:14 |
| R42.htm | 17398 | 2017-03-01 20:09:14 |
| R43.htm | 13405 | 2017-03-01 20:09:14 |
| R44.htm | 22060 | 2017-03-01 20:09:14 |
| R45.htm | 42793 | 2017-03-01 20:09:14 |
| R46.htm | 21216 | 2017-03-01 20:09:14 |
| R47.htm | 32257 | 2017-03-01 20:09:14 |
| R48.htm | 31952 | 2017-03-01 20:09:14 |
| R49.htm | 33625 | 2017-03-01 20:09:14 |
| R5.htm | 31707 | 2017-03-01 20:09:14 |
| R50.htm | 25849 | 2017-03-01 20:09:14 |
| R51.htm | 26709 | 2017-03-01 20:09:14 |
| R52.htm | 135852 | 2017-03-01 20:09:14 |
| R53.htm | 26554 | 2017-03-01 20:09:14 |
| R54.htm | 90046 | 2017-03-01 20:09:14 |
| R55.htm | 42241 | 2017-03-01 20:09:14 |
| R56.htm | 64161 | 2017-03-01 20:09:14 |
| R57.htm | 139705 | 2017-03-01 20:09:14 |
| R58.htm | 283959 | 2017-03-01 20:09:14 |
| R59.htm | 32003 | 2017-03-01 20:09:14 |
| R6.htm | 54086 | 2017-03-01 20:09:14 |
| R60.htm | 11660 | 2017-03-01 20:09:14 |
| R61.htm | 20300 | 2017-03-01 20:09:14 |
| R62.htm | 30062 | 2017-03-01 20:09:14 |
| R63.htm | 66752 | 2017-03-01 20:09:14 |
| R64.htm | 15580 | 2017-03-01 20:09:14 |
| R65.htm | 19384 | 2017-03-01 20:09:14 |
| R66.htm | 11825 | 2017-03-01 20:09:14 |
| R67.htm | 52919 | 2017-03-01 20:09:14 |
| R68.htm | 14706 | 2017-03-01 20:09:14 |
| R69.htm | 11956 | 2017-03-01 20:09:14 |
| R7.htm | 31370 | 2017-03-01 20:09:14 |
| R70.htm | 74189 | 2017-03-01 20:09:14 |
| R71.htm | 69605 | 2017-03-01 20:09:14 |
| R72.htm | 51932 | 2017-03-01 20:09:14 |
| R73.htm | 11665 | 2017-03-01 20:09:14 |
| R74.htm | 17866 | 2017-03-01 20:09:14 |
| R75.htm | 154992 | 2017-03-01 20:09:14 |
| R76.htm | 68573 | 2017-03-01 20:09:14 |
| R77.htm | 105004 | 2017-03-01 20:09:14 |
| R78.htm | 103146 | 2017-03-01 20:09:14 |
| R79.htm | 79865 | 2017-03-01 20:09:14 |
| R8.htm | 134124 | 2017-03-01 20:09:14 |
| R80.htm | 16762 | 2017-03-01 20:09:14 |
| R81.htm | 15298 | 2017-03-01 20:09:14 |
| R82.htm | 17273 | 2017-03-01 20:09:14 |
| R83.htm | 40416 | 2017-03-01 20:09:14 |
| R84.htm | 22148 | 2017-03-01 20:09:14 |
| R85.htm | 16830 | 2017-03-01 20:09:14 |
| R86.htm | 8504 | 2017-03-01 20:09:14 |
| R87.htm | 49480 | 2017-03-01 20:09:14 |
| R88.htm | 77310 | 2017-03-01 20:09:14 |
| R89.htm | 9751 | 2017-03-01 20:09:14 |
| R9.htm | 65467 | 2017-03-01 20:09:14 |
| R90.htm | 58085 | 2017-03-01 20:09:14 |
| R91.htm | 48410 | 2017-03-01 20:09:14 |
| R92.htm | 33851 | 2017-03-01 20:09:14 |
| R93.htm | 95104 | 2017-03-01 20:09:14 |
| R94.htm | 9524 | 2017-03-01 20:09:14 |
| R95.htm | 34316 | 2017-03-01 20:09:14 |
| R96.htm | 6484 | 2017-03-01 20:09:14 |
| R97.htm | 9073 | 2017-03-01 20:09:14 |
| R98.htm | 10022 | 2017-03-01 20:09:14 |
| R99.htm | 23986 | 2017-03-01 20:09:14 |
| report.css | 2768 | 2017-03-01 20:09:14 |
| Show.js | 1411 | 2017-03-01 20:09:14 |