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Loans - Schedule of Loans by Class (Details) - USD ($) $ in Millions | 12 Months Ended |  |
--- | --- | --- | ---
Dec. 31, 2020 | Dec. 31, 2019 | Dec. 31, 2018 | Sep. 30, 2020 | Dec. 31, 2017
Loans and Leases Receivable |  |  |  |  |
Loans and Leases Receivable, Deferred Income | $ (21.0) | $ (5.5) |  |  |
Mortgage loans held for sale, at fair value | 74.0 | 100.9 |  |  |
Total loans | 9,807.5 | 8,930.7 |  |  |
Accounts Receivable, Allowance for Credit Loss | (144.3) | (73.0) | $ (73.0) | $ (73.0) | $ (72.1)
Loans and Leases Receivable, Net Amount | 9,663.2 | 8,857.7 |  |  |
Loans, principally due to allowance for credit losses | (36.5) | (18.1) |  |  |
Less loans charged-off | (20.9) | (23.6) | $ (19.7) |  |
Financing Receivable, Allowance for Credit Loss, Recovery | 6.7 |  |  |  |
Financing Receivable, Allowance for Credit Losses, Effect of Change in Method | 55.5 |  |  |  |
Cumulative-Effect Adjustment, Consolidation of Variable Interest Entity |  |  |  |  |
Loans and Leases Receivable |  |  |  |  |
Accounts Receivable, Allowance for Credit Loss | (30.0) |  |  |  |
Commercial Real Estate Portfolio Segment [Member] |  |  |  |  |
Loans and Leases Receivable |  |  |  |  |
Loans held for investment | 3,743.2 | 3,487.8 |  |  |
Accounts Receivable, Allowance for Credit Loss | (54.8) |  |  | (19.5) |
Loans, principally due to allowance for credit losses | (20.1) |  |  |  |
Less loans charged-off | (0.4) |  |  |  |
Financing Receivable, Allowance for Credit Loss, Recovery | 0.3 |  |  |  |
Commercial Real Estate Portfolio Segment [Member] | Cumulative-Effect Adjustment, Consolidation of Variable Interest Entity |  |  |  |  |
Loans and Leases Receivable |  |  |  |  |
Accounts Receivable, Allowance for Credit Loss | (15.3) |  |  |  |
Residential Real Estate Construction Financing Receivable [Member] |  |  |  |  |
Loans and Leases Receivable |  |  |  |  |
Loans held for investment | 250.9 | 244.1 |  |  |
Total loans | 250.9 |  |  |  |
Accounts Receivable, Allowance for Credit Loss | (1.6) |  |  | (1.5) |
Loans, principally due to allowance for credit losses | (1.0) |  |  |  |
Less loans charged-off | 0.0 |  |  |  |
Financing Receivable, Allowance for Credit Loss, Recovery | 0.0 |  |  |  |
Residential Real Estate Construction Financing Receivable [Member] | Cumulative-Effect Adjustment, Consolidation of Variable Interest Entity |  |  |  |  |
Loans and Leases Receivable |  |  |  |  |
Accounts Receivable, Allowance for Credit Loss | 0.9 |  |  |  |
Commercial Real Estate Construction [Member] |  |  |  |  |
Loans and Leases Receivable |  |  |  |  |
Loans held for investment | 523.5 | 431.5 |  |  |
Total loans | 523.5 |  |  |  |
Accounts Receivable, Allowance for Credit Loss | (7.3) |  |  | (2.7) |
Loans, principally due to allowance for credit losses | (3.3) |  |  |  |
Less loans charged-off | 0.0 |  |  |  |
Financing Receivable, Allowance for Credit Loss, Recovery | 0.0 |  |  |  |
Commercial Real Estate Construction [Member] | Cumulative-Effect Adjustment, Consolidation of Variable Interest Entity |  |  |  |  |
Loans and Leases Receivable |  |  |  |  |
Accounts Receivable, Allowance for Credit Loss | (1.3) |  |  |  |
Real Estate Construction Financing Receivable [Member] |  |  |  |  |
Loans and Leases Receivable |  |  |  |  |
Loans held for investment | 1,039.4 | 977.7 |  |  |
Residential Mortgage [Member] |  |  |  |  |
Loans and Leases Receivable |  |  |  |  |
Loans held for investment | 1,396.3 | 1,246.1 |  |  |
Agricultural Real Estate Financing Receivable [Member] |  |  |  |  |
Loans and Leases Receivable |  |  |  |  |
Loans held for investment | 220.6 | 226.6 |  |  |
Total loans | 220.6 |  |  |  |
Accounts Receivable, Allowance for Credit Loss | (2.7) |  |  | (0.5) |
Loans, principally due to allowance for credit losses | (0.4) |  |  |  |
Less loans charged-off | 0.0 |  |  |  |
Financing Receivable, Allowance for Credit Loss, Recovery | 0.0 |  |  |  |
Agricultural Real Estate Financing Receivable [Member] | Cumulative-Effect Adjustment, Consolidation of Variable Interest Entity |  |  |  |  |
Loans and Leases Receivable |  |  |  |  |
Accounts Receivable, Allowance for Credit Loss | (1.8) |  |  |  |
Real Estate Financing Receivable [Member] |  |  |  |  |
Loans and Leases Receivable |  |  |  |  |
Loans held for investment | 6,399.5 | 5,938.2 |  |  |
Accounts Receivable, Allowance for Credit Loss | (80.5) |  |  | (28.9) |
Loans, principally due to allowance for credit losses | (22.9) |  |  |  |
Less loans charged-off | (0.9) |  |  |  |
Financing Receivable, Allowance for Credit Loss, Recovery | 1.1 |  |  |  |
Real Estate Financing Receivable [Member] | Cumulative-Effect Adjustment, Consolidation of Variable Interest Entity |  |  |  |  |
Loans and Leases Receivable |  |  |  |  |
Accounts Receivable, Allowance for Credit Loss | (28.5) |  |  |  |
Indirect consumer |  |  |  |  |
Loans and Leases Receivable |  |  |  |  |
Loans held for investment | 805.1 | 784.6 |  |  |
Total loans | 805.1 |  |  |  |
Accounts Receivable, Allowance for Credit Loss | (16.7) |  |  | (4.5) |
Loans, principally due to allowance for credit losses | (5.4) |  |  |  |
Less loans charged-off | (4.1) |  |  |  |
Financing Receivable, Allowance for Credit Loss, Recovery | 2.1 |  |  |  |
Indirect consumer | Cumulative-Effect Adjustment, Consolidation of Variable Interest Entity |  |  |  |  |
Loans and Leases Receivable |  |  |  |  |
Accounts Receivable, Allowance for Credit Loss | (8.8) |  |  |  |
Other consumer |  |  |  |  |
Loans and Leases Receivable |  |  |  |  |
Loans held for investment | 150.6 | 179.0 |  |  |
Total loans | 150.6 |  |  |  |
Accounts Receivable, Allowance for Credit Loss | (4.6) |  |  | (2.9) |
Loans, principally due to allowance for credit losses | (1.6) |  |  |  |
Less loans charged-off | (3.9) |  |  |  |
Financing Receivable, Allowance for Credit Loss, Recovery | 1.0 |  |  |  |
Other consumer | Cumulative-Effect Adjustment, Consolidation of Variable Interest Entity |  |  |  |  |
Loans and Leases Receivable |  |  |  |  |
Accounts Receivable, Allowance for Credit Loss | (3.0) |  |  |  |
Credit card consumer |  |  |  |  |
Loans and Leases Receivable |  |  |  |  |
Loans held for investment | 70.2 | 81.6 |  |  |
Accounts Receivable, Allowance for Credit Loss | (2.6) |  |  | (2.5) |
Loans, principally due to allowance for credit losses | (1.8) |  |  |  |
Less loans charged-off | (2.8) |  |  |  |
Financing Receivable, Allowance for Credit Loss, Recovery | 0.8 |  |  |  |
Credit card consumer | Cumulative-Effect Adjustment, Consolidation of Variable Interest Entity |  |  |  |  |
Loans and Leases Receivable |  |  |  |  |
Accounts Receivable, Allowance for Credit Loss | (0.3) |  |  |  |
Total consumer loans |  |  |  |  |
Loans and Leases Receivable |  |  |  |  |
Loans held for investment | 1,025.9 | 1,045.2 |  |  |
Accounts Receivable, Allowance for Credit Loss | (23.9) |  |  | (9.9) |
Loans, principally due to allowance for credit losses | (8.8) |  |  |  |
Less loans charged-off | (10.8) |  |  |  |
Financing Receivable, Allowance for Credit Loss, Recovery | 3.9 |  |  |  |
Total consumer loans | Cumulative-Effect Adjustment, Consolidation of Variable Interest Entity |  |  |  |  |
Loans and Leases Receivable |  |  |  |  |
Accounts Receivable, Allowance for Credit Loss | (12.1) |  |  |  |
Commercial Portfolio Segment [Member] |  |  |  |  |
Loans and Leases Receivable |  |  |  |  |
Loans held for investment | 2,153.9 | 1,673.7 |  |  |
Accounts Receivable, Allowance for Credit Loss | (39.2) |  |  | (32.6) |
Loans, principally due to allowance for credit losses | (24.0) |  |  |  |
Less loans charged-off | (9.1) |  |  |  |
Financing Receivable, Allowance for Credit Loss, Recovery | 1.7 |  |  |  |
Commercial Portfolio Segment [Member] | Cumulative-Effect Adjustment, Consolidation of Variable Interest Entity |  |  |  |  |
Loans and Leases Receivable |  |  |  |  |
Accounts Receivable, Allowance for Credit Loss | 10.0 |  |  |  |
Agricultural Financing Receivable [Member] |  |  |  |  |
Loans and Leases Receivable |  |  |  |  |
Loans held for investment | 247.6 | 279.1 |  |  |
Accounts Receivable, Allowance for Credit Loss | (0.7) |  |  | (1.6) |
Loans, principally due to allowance for credit losses | (0.2) |  |  |  |
Less loans charged-off | (0.1) |  |  |  |
Financing Receivable, Allowance for Credit Loss, Recovery | 0.0 |  |  |  |
Agricultural Financing Receivable [Member] | Cumulative-Effect Adjustment, Consolidation of Variable Interest Entity |  |  |  |  |
Loans and Leases Receivable |  |  |  |  |
Accounts Receivable, Allowance for Credit Loss | 0.6 |  |  |  |
Other, including overdrafts |  |  |  |  |
Loans and Leases Receivable |  |  |  |  |
Loans held for investment | 1.6 | 0.0 |  |  |
Loans held for investment |  |  |  |  |
Loans and Leases Receivable |  |  |  |  |
Loans held for investment | 9,828.5 | 8,936.2 |  |  |
FIBK Commercial Real Estate Non Owner Occupied Loans |  |  |  |  |
Loans and Leases Receivable |  |  |  |  |
Total loans | 1,674.5 |  |  |  |
Accounts Receivable, Allowance for Credit Loss | (25.5) |  |  | (8.8) |
Loans, principally due to allowance for credit losses | (11.7) |  |  |  |
Less loans charged-off | 0.0 |  |  |  |
FIBK Commercial Real Estate Non Owner Occupied Loans | Cumulative-Effect Adjustment, Consolidation of Variable Interest Entity |  |  |  |  |
Loans and Leases Receivable |  |  |  |  |
Accounts Receivable, Allowance for Credit Loss | (4.9) |  |  |  |
Financing Receivable, Allowance for Credit Loss, Recovery | 0.1 |  |  |  |
Commercial Real Estate Owner Occupied |  |  |  |  |
Loans and Leases Receivable |  |  |  |  |
Total loans | 1,705.0 |  |  |  |
Accounts Receivable, Allowance for Credit Loss | (18.3) |  |  | (10.0) |
Loans, principally due to allowance for credit losses | (5.0) |  |  |  |
Less loans charged-off | (0.4) |  |  |  |
Financing Receivable, Allowance for Credit Loss, Recovery | 0.2 |  |  |  |
Commercial Real Estate Owner Occupied | Cumulative-Effect Adjustment, Consolidation of Variable Interest Entity |  |  |  |  |
Loans and Leases Receivable |  |  |  |  |
Accounts Receivable, Allowance for Credit Loss | (3.5) |  |  |  |
Commercial Real Estate Multifamily |  |  |  |  |
Loans and Leases Receivable |  |  |  |  |
Total loans | 363.7 |  |  |  |
Accounts Receivable, Allowance for Credit Loss | (11.0) |  |  | (0.7) |
Loans, principally due to allowance for credit losses | (3.4) |  |  |  |
Less loans charged-off | 0.0 |  |  |  |
Financing Receivable, Allowance for Credit Loss, Recovery | 0.0 |  |  |  |
Commercial Real Estate Multifamily | Cumulative-Effect Adjustment, Consolidation of Variable Interest Entity |  |  |  |  |
Loans and Leases Receivable |  |  |  |  |
Accounts Receivable, Allowance for Credit Loss | (6.9) |  |  |  |
Land Acquisition And Development Construction Financing Receivable [Member] |  |  |  |  |
Loans and Leases Receivable |  |  |  |  |
Loans held for investment | 265.0 | $ 302.1 |  |  |
Total loans | 265.0 |  |  |  |
Accounts Receivable, Allowance for Credit Loss | (1.3) |  |  | (1.9) |
Loans, principally due to allowance for credit losses | (0.4) |  |  |  |
Less loans charged-off | (0.5) |  |  |  |
Financing Receivable, Allowance for Credit Loss, Recovery | 0.4 |  |  |  |
Land Acquisition And Development Construction Financing Receivable [Member] | Cumulative-Effect Adjustment, Consolidation of Variable Interest Entity |  |  |  |  |
Loans and Leases Receivable |  |  |  |  |
Accounts Receivable, Allowance for Credit Loss | 0.1 |  |  |  |
Construction Loans |  |  |  |  |
Loans and Leases Receivable |  |  |  |  |
Accounts Receivable, Allowance for Credit Loss | (10.2) |  |  | (6.1) |
Loans, principally due to allowance for credit losses | (3.9) |  |  |  |
Less loans charged-off | (0.5) |  |  |  |
Financing Receivable, Allowance for Credit Loss, Recovery | 0.4 |  |  |  |
Construction Loans | Cumulative-Effect Adjustment, Consolidation of Variable Interest Entity |  |  |  |  |
Loans and Leases Receivable |  |  |  |  |
Accounts Receivable, Allowance for Credit Loss | (0.3) |  |  |  |
Residential Real Estate 1-4 Family |  |  |  |  |
Loans and Leases Receivable |  |  |  |  |
Total loans | 1,012.3 |  |  |  |
Accounts Receivable, Allowance for Credit Loss | (11.4) |  |  | (1.8) |
Loans, principally due to allowance for credit losses | (1.1) |  |  |  |
Less loans charged-off | 0.0 |  |  |  |
Financing Receivable, Allowance for Credit Loss, Recovery | 0.1 |  |  |  |
Residential Real Estate 1-4 Family | Cumulative-Effect Adjustment, Consolidation of Variable Interest Entity |  |  |  |  |
Loans and Leases Receivable |  |  |  |  |
Accounts Receivable, Allowance for Credit Loss | (10.6) |  |  |  |
Home Equity Loan |  |  |  |  |
Loans and Leases Receivable |  |  |  |  |
Total loans | 384.0 |  |  |  |
Accounts Receivable, Allowance for Credit Loss | (1.4) |  |  | (1.0) |
Loans, principally due to allowance for credit losses | (0.4) |  |  |  |
Less loans charged-off | 0.0 |  |  |  |
Financing Receivable, Allowance for Credit Loss, Recovery | 0.3 |  |  |  |
Home Equity Loan | Cumulative-Effect Adjustment, Consolidation of Variable Interest Entity |  |  |  |  |
Loans and Leases Receivable |  |  |  |  |
Accounts Receivable, Allowance for Credit Loss | (0.5) |  |  |  |
Residential Real Estate |  |  |  |  |
Loans and Leases Receivable |  |  |  |  |
Accounts Receivable, Allowance for Credit Loss | (12.8) |  |  | (2.8) |
Loans, principally due to allowance for credit losses | (1.5) |  |  |  |
Less loans charged-off | 0.0 |  |  |  |
Financing Receivable, Allowance for Credit Loss, Recovery | 0.4 |  |  |  |
Residential Real Estate | Cumulative-Effect Adjustment, Consolidation of Variable Interest Entity |  |  |  |  |
Loans and Leases Receivable |  |  |  |  |
Accounts Receivable, Allowance for Credit Loss | (11.1) |  |  |  |
Commercial and Floor Plans |  |  |  |  |
Loans and Leases Receivable |  |  |  |  |
Total loans | 1,814.5 |  |  |  |
Accounts Receivable, Allowance for Credit Loss | (34.2) |  |  | (25.5) |
Loans, principally due to allowance for credit losses | (20.4) |  |  |  |
Less loans charged-off | (8.0) |  |  |  |
Financing Receivable, Allowance for Credit Loss, Recovery | 1.4 |  |  |  |
Commercial and Floor Plans | Cumulative-Effect Adjustment, Consolidation of Variable Interest Entity |  |  |  |  |
Loans and Leases Receivable |  |  |  |  |
Accounts Receivable, Allowance for Credit Loss | 5.1 |  |  |  |
Commercial Purpose Secured by 1-4 Family |  |  |  |  |
Loans and Leases Receivable |  |  |  |  |
Total loans | 272.8 |  |  |  |
Accounts Receivable, Allowance for Credit Loss | (4.7) |  |  | (5.9) |
Loans, principally due to allowance for credit losses | (2.5) |  |  |  |
Less loans charged-off | (0.1) |  |  |  |
Financing Receivable, Allowance for Credit Loss, Recovery | 0.2 |  |  |  |
Commercial Purpose Secured by 1-4 Family | Cumulative-Effect Adjustment, Consolidation of Variable Interest Entity |  |  |  |  |
Loans and Leases Receivable |  |  |  |  |
Accounts Receivable, Allowance for Credit Loss | 3.8 |  |  |  |
Commercial Borrower |  |  |  |  |
Loans and Leases Receivable |  |  |  |  |
Accounts Receivable, Allowance for Credit Loss | (0.3) |  |  | $ (1.2) |
Loans, principally due to allowance for credit losses | (1.1) |  |  |  |
Less loans charged-off | (1.0) |  |  |  |
Financing Receivable, Allowance for Credit Loss, Recovery | 0.1 |  |  |  |
Commercial Borrower | Cumulative-Effect Adjustment, Consolidation of Variable Interest Entity |  |  |  |  |
Loans and Leases Receivable |  |  |  |  |
Accounts Receivable, Allowance for Credit Loss | $ 1.1 |  |  |  |

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