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Fair Value Measurements - Schedule of Financial Assets and Financial Liabilities Measured at Fair Value on a Recurring and Non-Recurring Basis (Details) - USD ($) $ in Millions | 3 Months Ended |
--- | --- | ---
Mar. 31, 2020 | Mar. 31, 2019 | Dec. 31, 2019
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Investment debt securities available-for-sale | $ 3,000.3 |  | $ 2,960.0
Derivative assets | 65.1 |  | 23.2
Derivative liabilities | 59.5 |  | 22.2
Related Allowance |  |  | 3.6
Write downs | 0.0 | $ (0.3) |
Quoted Prices in Active Markets for Identical Assets (Level 1) | Fair Value Measured on a Recurring Basis |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Loans held for sale | 0.0 |  | 0.0
Deferred compensation plan assets | 0.0 |  | 0.0
Deferred compensation plan liabilities | 0.0 |  | 0.0
Significant Other Observable Inputs (Level 2) | Fair Value Measured on a Recurring Basis |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Loans held for sale | 94.4 |  | 100.9
Deferred compensation plan assets | 17.3 |  | 18.2
Deferred compensation plan liabilities | 17.3 |  | 18.2
Significant Unobservable Inputs (Level 3) | Fair Value Measured on a Recurring Basis |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Loans held for sale | 0.0 |  | 0.0
Deferred compensation plan assets | 0.0 |  | 0.0
Deferred compensation plan liabilities | 0.0 |  | 0.0
Significant Unobservable Inputs (Level 3) | Fair Value Measured on a Non-recurring Basis |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Related Allowance | 2.1 |  | 3.6
Partial loan charge-offs | 0.2 |  | 10.1
U.S. Treasury Notes |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Investment debt securities available-for-sale | 17.1 |  | 9.0
U.S. Treasury Notes | Quoted Prices in Active Markets for Identical Assets (Level 1) | Fair Value Measured on a Recurring Basis |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Investment debt securities available-for-sale | 0.0 |  | 0.0
U.S. Treasury Notes | Significant Other Observable Inputs (Level 2) | Fair Value Measured on a Recurring Basis |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Investment debt securities available-for-sale | 17.1 |  | 9.0
U.S. Treasury Notes | Significant Unobservable Inputs (Level 3) | Fair Value Measured on a Recurring Basis |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Investment debt securities available-for-sale | 0.0 |  | 0.0
State, county and municipal securities |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Investment debt securities available-for-sale | 112.3 |  | 80.9
State, county and municipal securities | Quoted Prices in Active Markets for Identical Assets (Level 1) | Fair Value Measured on a Recurring Basis |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Investment debt securities available-for-sale | 0.0 |  | 0.0
State, county and municipal securities | Significant Other Observable Inputs (Level 2) | Fair Value Measured on a Recurring Basis |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Investment debt securities available-for-sale | 112.3 |  | 80.9
State, county and municipal securities | Significant Unobservable Inputs (Level 3) | Fair Value Measured on a Recurring Basis |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Investment debt securities available-for-sale | 0.0 |  | 0.0
Obligations of U.S. government agencies |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Investment debt securities available-for-sale | 203.6 |  | 366.8
Obligations of U.S. government agencies | Quoted Prices in Active Markets for Identical Assets (Level 1) | Fair Value Measured on a Recurring Basis |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Investment debt securities available-for-sale | 0.0 |  | 0.0
Obligations of U.S. government agencies | Significant Other Observable Inputs (Level 2) | Fair Value Measured on a Recurring Basis |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Investment debt securities available-for-sale | 203.6 |  | 366.8
Obligations of U.S. government agencies | Significant Unobservable Inputs (Level 3) | Fair Value Measured on a Recurring Basis |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Investment debt securities available-for-sale | 0.0 |  | 0.0
U.S. agency residential mortgage-backed securities & collateralized mortgage obligations |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Investment debt securities available-for-sale | 2,414.8 |  | 2,317.2
U.S. agency residential mortgage-backed securities & collateralized mortgage obligations | Quoted Prices in Active Markets for Identical Assets (Level 1) | Fair Value Measured on a Recurring Basis |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Investment debt securities available-for-sale | 0.0 |  | 0.0
U.S. agency residential mortgage-backed securities & collateralized mortgage obligations | Significant Other Observable Inputs (Level 2) | Fair Value Measured on a Recurring Basis |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Investment debt securities available-for-sale | 2,414.8 |  | 2,317.2
U.S. agency residential mortgage-backed securities & collateralized mortgage obligations | Significant Unobservable Inputs (Level 3) | Fair Value Measured on a Recurring Basis |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Investment debt securities available-for-sale | 0.0 |  | 0.0
Private mortgage-backed securities |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Investment debt securities available-for-sale | 40.0 |  | 47.2
Private mortgage-backed securities | Quoted Prices in Active Markets for Identical Assets (Level 1) | Fair Value Measured on a Recurring Basis |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Investment debt securities available-for-sale | 0.0 |  | 0.0
Private mortgage-backed securities | Significant Other Observable Inputs (Level 2) | Fair Value Measured on a Recurring Basis |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Investment debt securities available-for-sale | 40.0 |  | 47.2
Private mortgage-backed securities | Significant Unobservable Inputs (Level 3) | Fair Value Measured on a Recurring Basis |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Investment debt securities available-for-sale | 0.0 |  | 0.0
Corporate securities |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Investment debt securities available-for-sale | 210.5 |  | 135.7
Corporate securities | Quoted Prices in Active Markets for Identical Assets (Level 1) | Fair Value Measured on a Recurring Basis |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Investment debt securities available-for-sale | 0.0 |  | 0.0
Corporate securities | Significant Other Observable Inputs (Level 2) | Fair Value Measured on a Recurring Basis |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Investment debt securities available-for-sale | 210.5 |  | 135.7
Corporate securities | Significant Unobservable Inputs (Level 3) | Fair Value Measured on a Recurring Basis |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Investment debt securities available-for-sale | 0.0 |  | 0.0
Other investments |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Investment debt securities available-for-sale | 2.0 |  | 3.2
Other investments | Quoted Prices in Active Markets for Identical Assets (Level 1) | Fair Value Measured on a Recurring Basis |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Investment debt securities available-for-sale | 0.0 |  | 0.0
Other investments | Significant Other Observable Inputs (Level 2) | Fair Value Measured on a Recurring Basis |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Investment debt securities available-for-sale | 2.0 |  | 3.2
Other investments | Significant Unobservable Inputs (Level 3) | Fair Value Measured on a Recurring Basis |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Investment debt securities available-for-sale | 0.0 |  | 0.0
Collateral dependent loans | Quoted Prices in Active Markets for Identical Assets (Level 1) | Fair Value Measured on a Non-recurring Basis |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Collateral dependent loans | 0.0 |  | 0.0
Collateral dependent loans | Significant Other Observable Inputs (Level 2) | Fair Value Measured on a Non-recurring Basis |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Collateral dependent loans | 0.0 |  | 0.0
Collateral dependent loans | Significant Unobservable Inputs (Level 3) | Fair Value Measured on a Non-recurring Basis |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Collateral dependent loans |  |  | 27.3
Other real estate owned | Quoted Prices in Active Markets for Identical Assets (Level 1) | Fair Value Measured on a Non-recurring Basis |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Other real estate owned | 0.0 |  | 0.0
Other real estate owned | Significant Other Observable Inputs (Level 2) | Fair Value Measured on a Non-recurring Basis |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Other real estate owned | 0.0 |  | 0.0
Other real estate owned | Significant Unobservable Inputs (Level 3) | Fair Value Measured on a Non-recurring Basis |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Other real estate owned | 2.3 |  | 2.2
Estimated Fair Value |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Investment debt securities available-for-sale | 3,000.3 |  | 2,960.0
Derivative assets | 65.1 |  | 23.2
Derivative liabilities | 59.5 |  | 22.2
Deferred compensation plan assets | 17.3 |  | 18.2
Deferred compensation plan liabilities | 17.3 |  | 18.2
Estimated Fair Value | Fair Value Measured on a Recurring Basis |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Loans held for sale | 94.4 |  | 100.9
Deferred compensation plan assets | 17.3 |  | 18.2
Deferred compensation plan liabilities | 17.3 |  | 18.2
Estimated Fair Value | Fair Value Measured on a Non-recurring Basis |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Long-lived assets to be disposed of by sale | 5.0 |  | 6.2
Estimated Fair Value | Quoted Prices in Active Markets for Identical Assets (Level 1) |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Investment debt securities available-for-sale | 0.0 |  | 0.0
Derivative assets | 0.0 |  | 0.0
Derivative liabilities | 0.0 |  | 0.0
Deferred compensation plan assets | 0.0 |  | 0.0
Deferred compensation plan liabilities | 0.0 |  | 0.0
Estimated Fair Value | Significant Other Observable Inputs (Level 2) |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Investment debt securities available-for-sale | 3,000.3 |  | 2,960.0
Derivative assets | 65.1 |  | 23.2
Derivative liabilities | 59.5 |  | 22.2
Deferred compensation plan assets | 17.3 |  | 18.2
Deferred compensation plan liabilities | 17.3 |  | 18.2
Estimated Fair Value | Significant Unobservable Inputs (Level 3) |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Investment debt securities available-for-sale | 0.0 |  | 0.0
Derivative assets | 0.0 |  | 0.0
Derivative liabilities | 0.0 |  | 0.0
Deferred compensation plan assets | 0.0 |  | 0.0
Deferred compensation plan liabilities | 0.0 |  | 0.0
Estimated Fair Value | Significant Unobservable Inputs (Level 3) | Fair Value Measured on a Non-recurring Basis |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Collateral dependent loans | 3.6 |  | 27.6
Estimated Fair Value | U.S. Treasury Notes | Fair Value Measured on a Recurring Basis |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Investment debt securities available-for-sale | 17.1 |  | 9.0
Estimated Fair Value | State, county and municipal securities | Fair Value Measured on a Recurring Basis |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Investment debt securities available-for-sale | 112.3 |  | 80.9
Estimated Fair Value | Obligations of U.S. government agencies | Fair Value Measured on a Recurring Basis |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Investment debt securities available-for-sale | 203.6 |  | 366.8
Estimated Fair Value | U.S. agency residential mortgage-backed securities & collateralized mortgage obligations | Fair Value Measured on a Recurring Basis |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Investment debt securities available-for-sale | 2,414.8 |  | 2,317.2
Estimated Fair Value | Private mortgage-backed securities | Fair Value Measured on a Recurring Basis |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Investment debt securities available-for-sale | 40.0 |  | 47.2
Estimated Fair Value | Corporate securities | Fair Value Measured on a Recurring Basis |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Investment debt securities available-for-sale | 210.5 |  | 135.7
Estimated Fair Value | Other investments | Fair Value Measured on a Recurring Basis |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Investment debt securities available-for-sale | 2.0 |  | 3.2
Estimated Fair Value | Collateral dependent loans | Significant Unobservable Inputs (Level 3) | Fair Value Measured on a Non-recurring Basis |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Collateral dependent loans | 3.6 |  | 27.3
Estimated Fair Value | Other real estate owned | Significant Unobservable Inputs (Level 3) | Fair Value Measured on a Non-recurring Basis |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Other real estate owned | 2.3 |  | 2.2
Carrying Amount |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Investment debt securities available-for-sale | 3,000.3 |  | 2,960.0
Derivative assets | 65.1 |  | 23.2
Derivative liabilities | 59.5 |  | 22.2
Deferred compensation plan assets | 17.3 |  | 18.2
Deferred compensation plan liabilities | 17.3 |  | 18.2
Carrying Amount | Significant Unobservable Inputs (Level 3) | Fair Value Measured on a Non-recurring Basis |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Collateral dependent loans | 5.9 |  | 41.3
Long-lived assets to be disposed of by sale | 5.2 |  | 6.4
Change During Period | Fair Value Measured on a Non-recurring Basis |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Long-lived assets to be disposed of by sale | 0.2 |  | 0.2
Interest Rate Swap |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Derivative assets | 57.4 |  | 21.9
Derivative liabilities | 57.4 |  | 21.9
Interest Rate Swap | Quoted Prices in Active Markets for Identical Assets (Level 1) | Fair Value Measured on a Recurring Basis |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Derivative assets | 0.0 |  | 0.0
Derivative liabilities | 0.0 |  | 0.0
Interest Rate Swap | Significant Other Observable Inputs (Level 2) | Fair Value Measured on a Recurring Basis |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Derivative assets | 57.4 |  | 21.9
Derivative liabilities | 57.4 |  | 21.9
Interest Rate Swap | Significant Unobservable Inputs (Level 3) | Fair Value Measured on a Recurring Basis |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Derivative assets | 0.0 |  | 0.0
Derivative liabilities | 0.0 |  | 0.0
Interest Rate Swap | Estimated Fair Value | Fair Value Measured on a Recurring Basis |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Derivative assets | 57.4 |  | 21.9
Derivative liabilities | 57.4 |  | 21.9
Interest Rate Lock Commitments | Quoted Prices in Active Markets for Identical Assets (Level 1) | Fair Value Measured on a Recurring Basis |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Derivative assets | 0.0 |  | 0.0
Interest Rate Lock Commitments | Significant Other Observable Inputs (Level 2) | Fair Value Measured on a Recurring Basis |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Derivative assets | 7.7 |  | 1.3
Interest Rate Lock Commitments | Significant Unobservable Inputs (Level 3) | Fair Value Measured on a Recurring Basis |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Derivative assets | 0.0 |  | 0.0
Interest Rate Lock Commitments | Estimated Fair Value | Fair Value Measured on a Recurring Basis |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Derivative assets | 7.7 |  | 1.3
Forward Contracts | Quoted Prices in Active Markets for Identical Assets (Level 1) | Fair Value Measured on a Recurring Basis |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Derivative liabilities | 0.0 |  | 0.0
Forward Contracts | Significant Other Observable Inputs (Level 2) | Fair Value Measured on a Recurring Basis |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Derivative liabilities | 2.1 |  | 0.3
Forward Contracts | Significant Unobservable Inputs (Level 3) | Fair Value Measured on a Recurring Basis |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Derivative liabilities | 0.0 |  | 0.0
Forward Contracts | Estimated Fair Value | Fair Value Measured on a Recurring Basis |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Derivative liabilities | 2.1 |  | 0.3
Long-lived assets to be disposed of by sale | Quoted Prices in Active Markets for Identical Assets (Level 1) | Fair Value Measured on a Non-recurring Basis |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Long-lived assets to be disposed of by sale | 0.0 |  | 0.0
Long-lived assets to be disposed of by sale | Significant Other Observable Inputs (Level 2) | Fair Value Measured on a Non-recurring Basis |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Long-lived assets to be disposed of by sale | 0.0 |  | 0.0
Long-lived assets to be disposed of by sale | Significant Unobservable Inputs (Level 3) | Fair Value Measured on a Non-recurring Basis |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Long-lived assets to be disposed of by sale | 5.0 |  | 6.2
Long-lived assets to be disposed of by sale | Estimated Fair Value | Significant Unobservable Inputs (Level 3) | Fair Value Measured on a Non-recurring Basis |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Long-lived assets to be disposed of by sale | $ 5.0 |  | $ 6.2

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