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Subordinated Debentures Held by Subsidiary Trusts (Details) $ in Millions |  | 1 Months Ended | 12 Months Ended |  |  |
--- | --- | --- | --- | --- | --- | ---
Aug. 16, 2018 | Dec. 31, 2007 | Dec. 31, 2022 USD ($) trusts | Dec. 31, 2011 | Dec. 31, 2021 USD ($) | May 31, 2020 | Nov. 30, 2007
Subordinated Borrowing |  |  |  |  |  |  |
Number of company sponsored wholly-owned business trusts | trusts |  |  | 14 |  |  |  |
Subordinated debentures held by subsidiary trusts |  |  |  |  | $ 87.0 |  |
Stated interest rate |  |  |  |  |  | 5.25% |
Subordinated Debt |  |  | $ 163.7 |  | 87.7 |  |
Subordinated Long-term Debt, Noncurrent |  |  | 163.1 |  | 87.0 |  |
Common Stock Held in Assets |  |  | 5.3 |  | 2.7 |  |
Subordinated Debt Fair Value Adjustment |  |  | (0.6) |  | (0.7) |  |
Junior Subordinated Deferrable Interest Debentures Issued by GWB Trust II |  |  |  |  |  |  |
Subordinated Borrowing |  |  |  |  |  |  |
Subordinated Debt |  |  | 2.0 |  |  |  |
Junior Subordinated Deferrable Interest Debentures Issued by INB Cap Trust I |  |  |  |  |  |  |
Subordinated Borrowing |  |  |  |  |  |  |
Subordinated Debt |  |  | 5.0 |  |  |  |
Junior Subordinated Deferrable Interest Debentures Issued by GWB Trust VI |  |  |  |  |  |  |
Subordinated Borrowing |  |  |  |  |  |  |
Subordinated Debt |  |  | 30.0 |  |  |  |
Junior Subordinated Deferrable Interest Debentures Issued by GWB Trust IV |  |  |  |  |  |  |
Subordinated Borrowing |  |  |  |  |  |  |
Subordinated Debt |  |  | 22.4 |  |  |  |
Junior Subordinated Deferrable Interest Debentures Issued by HFFC III |  |  |  |  |  |  |
Subordinated Borrowing |  |  |  |  |  |  |
Subordinated Debt |  |  | 5.0 |  |  |  |
Junior Subordinated Deferrable Interest Debentures Issued by HFFC IV |  |  |  |  |  |  |
Subordinated Borrowing |  |  |  |  |  |  |
Subordinated Debt |  |  | 7.0 |  |  |  |
Junior Subordinated Deferrable Interest Debentures Issued by HFFC V |  |  |  |  |  |  |
Subordinated Borrowing |  |  |  |  |  |  |
Subordinated Debt |  |  | 5.0 |  |  |  |
Junior Subordinated Deferrable Interest Debentures Issued by HFFC VI |  |  |  |  |  |  |
Subordinated Borrowing |  |  |  |  |  |  |
Subordinated Debt |  |  | 2.0 |  |  |  |
First Interstate Statutory Trust II | Junior Subordinated Deferrable Interest Debentures Issued by FIST II |  |  |  |  |  |  |
Subordinated Borrowing |  |  |  |  |  |  |
Subordinated Debt |  |  |  |  | 10.3 |  |
First Interstate Statutory Trust III | Junior Subordinated Deferrable Interest Debentures Issued by FIST III |  |  |  |  |  |  |
Subordinated Borrowing |  |  |  |  |  |  |
Subordinated Debt |  |  |  |  | 20.6 |  |
First Interstate Statutory Trust IV | Junior Subordinated Deferrable Interest Debentures Issued by FIST IV |  |  |  |  |  |  |
Subordinated Borrowing |  |  |  |  |  |  |
Subordinated Debt |  |  |  |  | 15.5 |  |
First Interstate Statutory Trust V | Junior Subordinated Deferrable Interest Debentures Issued by FIST V |  |  |  |  |  |  |
Subordinated Borrowing |  |  |  |  |  |  |
Subordinated Debt |  |  |  |  | 10.3 |  |
First Interstate Statutory Trust VI | Junior Subordinated Deferrable Interest Debentures Issued by FIST VI |  |  |  |  |  |  |
Subordinated Borrowing |  |  |  |  |  |  |
Subordinated Debt |  |  |  |  | 10.3 |  |
Northwest Bancorporation Capital Trust 1 [Member] | Junior Subordinated Deferrable Interest Debentures Issued by FIST VI |  |  |  |  |  |  |
Subordinated Borrowing |  |  |  |  |  |  |
Subordinated Debt |  |  |  |  | 5.2 |  |
Junior Subordinated Deferrable Interest Debentures Issued by GWB Trust II |  |  |  |  |  |  |
Subordinated Borrowing |  |  |  |  |  |  |
Common Stock Held in Assets |  |  | 0.1 |  | 0.0 |  |
Junior Subordinated Deferrable Interest Debentures Issued by GWB Trust II | Junior Subordinated Deferrable Interest Debentures Issued by GWB Trust II |  |  |  |  |  |  |
Subordinated Borrowing |  |  |  |  |  |  |
Subordinated Debt |  |  | $ 2.1 |  | 0.0 |  |
Debt instrument, basis spread on variable rate |  |  |  | 1.85% |  |  |
Junior Subordinated Deferrable Interest Debentures Issued by GWB Trust II | Junior Subordinated Deferrable Interest Debentures Issued by GWB Trust II | LIBOR |  |  |  |  |  |  |
Subordinated Borrowing |  |  |  |  |  |  |
Debt instrument, interest rate at period end |  |  | 6.62% |  |  |  |
Junior Subordinated Deferrable Interest Debentures Issued by FIST II |  |  |  |  |  |  |
Subordinated Borrowing |  |  |  |  |  |  |
Common Stock Held in Assets |  |  | $ 0.3 |  | 0.3 |  |
Junior Subordinated Deferrable Interest Debentures Issued by FIST II | Junior Subordinated Deferrable Interest Debentures Issued by FIST II |  |  |  |  |  |  |
Subordinated Borrowing |  |  |  |  |  |  |
Subordinated Debt |  |  | $ 10.3 |  |  |  |
Junior Subordinated Deferrable Interest Debentures Issued by FIST II | Junior Subordinated Deferrable Interest Debentures Issued by FIST II | Debt Instrument, Redemption, After Period Five |  |  |  |  |  |  |
Subordinated Borrowing |  |  |  |  |  |  |
Debt instrument, basis spread on variable rate |  | 2.25% |  |  |  |  |
Junior Subordinated Deferrable Interest Debentures Issued by FIST II | Junior Subordinated Deferrable Interest Debentures Issued by FIST II | LIBOR |  |  |  |  |  |  |
Subordinated Borrowing |  |  |  |  |  |  |
Debt instrument, interest rate at period end |  |  | 5.99% |  |  |  |
Junior Subordinated Deferrable Interest Debentures Issued by FIST I |  |  |  |  |  |  |
Subordinated Borrowing |  |  |  |  |  |  |
Common Stock Held in Assets |  |  | $ 0.5 |  | 0.5 |  |
Junior Subordinated Deferrable Interest Debentures Issued by FIST I | Junior Subordinated Deferrable Interest Debentures Issued by FIST I |  |  |  |  |  |  |
Subordinated Borrowing |  |  |  |  |  |  |
Subordinated Debt |  |  | $ 15.5 |  | 15.5 |  |
Junior Subordinated Deferrable Interest Debentures Issued by FIST I | Junior Subordinated Deferrable Interest Debentures Issued by FIST I | Debt Instrument, Redemption, After Period Five |  |  |  |  |  |  |
Subordinated Borrowing |  |  |  |  |  |  |
Debt instrument, basis spread on variable rate |  | 2.75% |  |  |  |  |
Junior Subordinated Deferrable Interest Debentures Issued by FIST I | Junior Subordinated Deferrable Interest Debentures Issued by FIST I | Debt Instrument, Redemption, At Issuance through Year Five [Member] |  |  |  |  |  |  |
Subordinated Borrowing |  |  |  |  |  |  |
Stated interest rate |  |  |  |  |  |  | 7.50%
Junior Subordinated Deferrable Interest Debentures Issued by FIST I | Junior Subordinated Deferrable Interest Debentures Issued by FIST I | LIBOR |  |  |  |  |  |  |
Subordinated Borrowing |  |  |  |  |  |  |
Debt instrument, interest rate at period end |  |  | 7.52% |  |  |  |
Junior Subordinated Deferrable Interest Debentures Issued by FIST III |  |  |  |  |  |  |
Subordinated Borrowing |  |  |  |  |  |  |
Common Stock Held in Assets |  |  | $ 0.6 |  | 0.6 |  |
Junior Subordinated Deferrable Interest Debentures Issued by FIST III | Junior Subordinated Deferrable Interest Debentures Issued by FIST III |  |  |  |  |  |  |
Subordinated Borrowing |  |  |  |  |  |  |
Subordinated Debt |  |  | $ 20.6 |  |  |  |
Junior Subordinated Deferrable Interest Debentures Issued by FIST III | Junior Subordinated Deferrable Interest Debentures Issued by FIST III | Debt Instrument, Redemption, After Period Five |  |  |  |  |  |  |
Subordinated Borrowing |  |  |  |  |  |  |
Debt instrument, basis spread on variable rate |  | 2.40% |  |  |  |  |
Junior Subordinated Deferrable Interest Debentures Issued by FIST III | Junior Subordinated Deferrable Interest Debentures Issued by FIST III | Debt Instrument, Redemption, At Issuance through Year Five [Member] |  |  |  |  |  |  |
Subordinated Borrowing |  |  |  |  |  |  |
Stated interest rate |  | 6.88% |  |  |  |  |
Junior Subordinated Deferrable Interest Debentures Issued by FIST III | Junior Subordinated Deferrable Interest Debentures Issued by FIST III | LIBOR |  |  |  |  |  |  |
Subordinated Borrowing |  |  |  |  |  |  |
Debt instrument, interest rate at period end |  |  | 7.17% |  |  |  |
Junior Subordinated Deferrable Interest Debentures Issued by FIST IV |  |  |  |  |  |  |
Subordinated Borrowing |  |  |  |  |  |  |
Common Stock Held in Assets |  |  | $ 0.5 |  | 0.5 |  |
Junior Subordinated Deferrable Interest Debentures Issued by FIST IV | Junior Subordinated Deferrable Interest Debentures Issued by FIST IV |  |  |  |  |  |  |
Subordinated Borrowing |  |  |  |  |  |  |
Debt instrument, interest rate at period end |  | 2.70% |  |  |  |  |
Subordinated Debt |  |  | $ 15.5 |  |  |  |
Junior Subordinated Deferrable Interest Debentures Issued by FIST IV | Junior Subordinated Deferrable Interest Debentures Issued by FIST IV | LIBOR |  |  |  |  |  |  |
Subordinated Borrowing |  |  |  |  |  |  |
Debt instrument, interest rate at period end |  |  | 6.44% |  |  |  |
Junior Subordinated Deferrable Interest Debentures Issued by FIST V |  |  |  |  |  |  |
Subordinated Borrowing |  |  |  |  |  |  |
Common Stock Held in Assets |  |  | $ 0.3 |  | 0.3 |  |
Junior Subordinated Deferrable Interest Debentures Issued by FIST V | Junior Subordinated Deferrable Interest Debentures Issued by FIST V |  |  |  |  |  |  |
Subordinated Borrowing |  |  |  |  |  |  |
Subordinated Debt |  |  | $ 10.3 |  |  |  |
Junior Subordinated Deferrable Interest Debentures Issued by FIST V | Junior Subordinated Deferrable Interest Debentures Issued by FIST V | Debt Instrument, Redemption, After Period Five |  |  |  |  |  |  |
Subordinated Borrowing |  |  |  |  |  |  |
Debt instrument, basis spread on variable rate |  |  |  | 2.75% |  |  |
Junior Subordinated Deferrable Interest Debentures Issued by FIST V | Junior Subordinated Deferrable Interest Debentures Issued by FIST V | Debt Instrument, Redemption, At Issuance through Year Five [Member] |  |  |  |  |  |  |
Subordinated Borrowing |  |  |  |  |  |  |
Stated interest rate |  | 6.78% |  |  |  |  |
Junior Subordinated Deferrable Interest Debentures Issued by FIST V | Junior Subordinated Deferrable Interest Debentures Issued by FIST V | LIBOR |  |  |  |  |  |  |
Subordinated Borrowing |  |  |  |  |  |  |
Debt instrument, interest rate at period end |  |  | 6.49% |  |  |  |
Junior Subordinated Deferrable Interest Debentures Issued by FIST VI |  |  |  |  |  |  |
Subordinated Borrowing |  |  |  |  |  |  |
Common Stock Held in Assets |  |  | $ 0.3 |  | 0.3 |  |
Junior Subordinated Deferrable Interest Debentures Issued by FIST VI | Junior Subordinated Deferrable Interest Debentures Issued by FIST VI |  |  |  |  |  |  |
Subordinated Borrowing |  |  |  |  |  |  |
Subordinated Debt |  |  | $ 10.3 |  |  |  |
Debt instrument, basis spread on variable rate |  |  |  | 2.75% |  |  |
Junior Subordinated Deferrable Interest Debentures Issued by FIST VI | Junior Subordinated Deferrable Interest Debentures Issued by FIST VI | LIBOR |  |  |  |  |  |  |
Subordinated Borrowing |  |  |  |  |  |  |
Debt instrument, interest rate at period end |  |  | 6.49% |  |  |  |
Junior Subordinated Deferrable Interest Debentures Issued by INB Cap Trust I |  |  |  |  |  |  |
Subordinated Borrowing |  |  |  |  |  |  |
Common Stock Held in Assets |  |  | $ 0.2 |  | 0.2 |  |
Junior Subordinated Deferrable Interest Debentures Issued by INB Cap Trust I | Junior Subordinated Deferrable Interest Debentures Issued by INB Cap Trust I |  |  |  |  |  |  |
Subordinated Borrowing |  |  |  |  |  |  |
Subordinated Debt |  |  | $ 5.2 |  |  |  |
Junior Subordinated Deferrable Interest Debentures Issued by INB Cap Trust I | Junior Subordinated Deferrable Interest Debentures Issued by INB Cap Trust I | Debt Instrument, Redemption, After Period Five |  |  |  |  |  |  |
Subordinated Borrowing |  |  |  |  |  |  |
Debt instrument, basis spread on variable rate | 1.70% |  |  |  |  |  |
Junior Subordinated Deferrable Interest Debentures Issued by INB Cap Trust I | Junior Subordinated Deferrable Interest Debentures Issued by INB Cap Trust I | Debt Instrument, Redemption, At Issuance through Year Five [Member] |  |  |  |  |  |  |
Subordinated Borrowing |  |  |  |  |  |  |
Stated interest rate |  | 5.95% |  |  |  |  |
Junior Subordinated Deferrable Interest Debentures Issued by INB Cap Trust I | Junior Subordinated Deferrable Interest Debentures Issued by INB Cap Trust I | LIBOR |  |  |  |  |  |  |
Subordinated Borrowing |  |  |  |  |  |  |
Debt instrument, interest rate at period end |  |  | 6.43% |  |  |  |
Junior Subordinated Deferrable Interest Debentures Issued by GWB Trust VI |  |  |  |  |  |  |
Subordinated Borrowing |  |  |  |  |  |  |
Common Stock Held in Assets |  |  | $ 0.9 |  | 0.0 |  |
Junior Subordinated Deferrable Interest Debentures Issued by GWB Trust VI | Junior Subordinated Deferrable Interest Debentures Issued by GWB Trust VI |  |  |  |  |  |  |
Subordinated Borrowing |  |  |  |  |  |  |
Subordinated Debt |  |  | $ 30.9 |  | 0.0 |  |
Debt instrument, basis spread on variable rate |  |  |  | 1.48% |  |  |
Junior Subordinated Deferrable Interest Debentures Issued by GWB Trust VI | Junior Subordinated Deferrable Interest Debentures Issued by GWB Trust VI | LIBOR |  |  |  |  |  |  |
Subordinated Borrowing |  |  |  |  |  |  |
Debt instrument, interest rate at period end |  |  | 6.25% |  |  |  |
Junior Subordinated Deferrable Interest Debentures Issued by GWB Trust IV |  |  |  |  |  |  |
Subordinated Borrowing |  |  |  |  |  |  |
Common Stock Held in Assets |  |  | $ 0.7 |  | 0.0 |  |
Junior Subordinated Deferrable Interest Debentures Issued by GWB Trust IV | Junior Subordinated Deferrable Interest Debentures Issued by GWB Trust IV |  |  |  |  |  |  |
Subordinated Borrowing |  |  |  |  |  |  |
Subordinated Debt |  |  | $ 23.1 |  | 0.0 |  |
Debt instrument, basis spread on variable rate |  |  |  | 2.85% |  |  |
Junior Subordinated Deferrable Interest Debentures Issued by GWB Trust IV | Junior Subordinated Deferrable Interest Debentures Issued by GWB Trust IV | LIBOR |  |  |  |  |  |  |
Subordinated Borrowing |  |  |  |  |  |  |
Debt instrument, interest rate at period end |  |  | 7.59% |  |  |  |
Junior Subordinated Deferrable Interest Debentures Issued by HFFC III |  |  |  |  |  |  |
Subordinated Borrowing |  |  |  |  |  |  |
Common Stock Held in Assets |  |  | $ 0.2 |  | 0.0 |  |
Junior Subordinated Deferrable Interest Debentures Issued by HFFC III | Junior Subordinated Deferrable Interest Debentures Issued by HFFC III |  |  |  |  |  |  |
Subordinated Borrowing |  |  |  |  |  |  |
Subordinated Debt |  |  | $ 5.2 |  | 0.0 |  |
Debt instrument, basis spread on variable rate |  |  |  | 3.35% |  |  |
Junior Subordinated Deferrable Interest Debentures Issued by HFFC III | Junior Subordinated Deferrable Interest Debentures Issued by HFFC III | LIBOR |  |  |  |  |  |  |
Subordinated Borrowing |  |  |  |  |  |  |
Debt instrument, interest rate at period end |  |  | 7.43% |  |  |  |
Junior Subordinated Deferrable Interest Debentures Issued by HFFC IV |  |  |  |  |  |  |
Subordinated Borrowing |  |  |  |  |  |  |
Common Stock Held in Assets |  |  | $ 0.2 |  | 0.0 |  |
Junior Subordinated Deferrable Interest Debentures Issued by HFFC IV | Junior Subordinated Deferrable Interest Debentures Issued by HFFC IV |  |  |  |  |  |  |
Subordinated Borrowing |  |  |  |  |  |  |
Subordinated Debt |  |  | $ 7.2 |  | 0.0 |  |
Debt instrument, basis spread on variable rate |  |  |  | 3.10% |  |  |
Junior Subordinated Deferrable Interest Debentures Issued by HFFC IV | Junior Subordinated Deferrable Interest Debentures Issued by HFFC IV | LIBOR |  |  |  |  |  |  |
Subordinated Borrowing |  |  |  |  |  |  |
Debt instrument, interest rate at period end |  |  | 7.18% |  |  |  |
Junior Subordinated Deferrable Interest Debentures Issued by HFFC V |  |  |  |  |  |  |
Subordinated Borrowing |  |  |  |  |  |  |
Common Stock Held in Assets |  |  | $ 0.3 |  | 0.0 |  |
Junior Subordinated Deferrable Interest Debentures Issued by HFFC V | Junior Subordinated Deferrable Interest Debentures Issued by HFFC V |  |  |  |  |  |  |
Subordinated Borrowing |  |  |  |  |  |  |
Subordinated Debt |  |  | $ 5.3 |  | 0.0 |  |
Debt instrument, basis spread on variable rate |  |  |  | 1.83% |  |  |
Junior Subordinated Deferrable Interest Debentures Issued by HFFC V | Junior Subordinated Deferrable Interest Debentures Issued by HFFC V | LIBOR |  |  |  |  |  |  |
Subordinated Borrowing |  |  |  |  |  |  |
Debt instrument, interest rate at period end |  |  | 6.59% |  |  |  |
Junior Subordinated Deferrable Interest Debentures Issued by HFFC VI |  |  |  |  |  |  |
Subordinated Borrowing |  |  |  |  |  |  |
Common Stock Held in Assets |  |  | $ 0.2 |  | 0.0 |  |
Junior Subordinated Deferrable Interest Debentures Issued by HFFC VI | Junior Subordinated Deferrable Interest Debentures Issued by HFFC VI |  |  |  |  |  |  |
Subordinated Borrowing |  |  |  |  |  |  |
Subordinated Debt |  |  | $ 2.2 |  | $ 0.0 |  |
Debt instrument, basis spread on variable rate |  |  |  | 1.65% |  |  |
Junior Subordinated Deferrable Interest Debentures Issued by HFFC VI | Junior Subordinated Deferrable Interest Debentures Issued by HFFC VI | LIBOR |  |  |  |  |  |  |
Subordinated Borrowing |  |  |  |  |  |  |
Debt instrument, interest rate at period end |  |  | 5.39% |  |  |  |
Trust Preferred Securities Subject to Mandatory Redemption | Trusts |  |  |  |  |  |  |
Subordinated Borrowing |  |  |  |  |  |  |
Business trust term (in years) |  |  | 30 years |  |  |  |
Common Stock Subject to Mandatory Redemption | Trusts |  |  |  |  |  |  |
Subordinated Borrowing |  |  |  |  |  |  |
Amount of financial instruments subject to mandatory redemption |  |  | $ 5.3 |  |  |  |
Subordinated Debentures Subject to Mandatory Redemption | Trusts |  |  |  |  |  |  |
Subordinated Borrowing |  |  |  |  |  |  |
Business trust term (in years) |  |  | 30 years |  |  |  |

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