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Fair Value Measurements - Schedule of Estimated Fair Values of Financial Instruments by Level of Valuation Inputs (Details) - USD ($) $ in Millions | Sep. 30, 2019 | Dec. 31, 2018
--- | --- | ---
Financial assets: |  |
Investment debt securities available-for-sale | $ 2,732.2 | $ 2,270.7
Investment debt securities held-to-maturity | 97.2 | 400.7
Derivative assets | 33.0 | 10.1
Financial liabilities: |  |
Derivative liabilities | 30.8 | 9.4
Carrying Amount |  |
Financial assets: |  |
Cash and cash equivalents | 1,269.6 | 822.0
Investment debt securities available-for-sale | 2,732.2 | 2,270.7
Investment debt securities held-to-maturity | 94.9 | 406.8
Accrued interest receivable | 51.1 | 44.9
Mortgage servicing rights, net | 29.8 | 27.7
Loans held for sale | 108.9 | 33.3
Net loans held for investment | 8,917.6 | 8,397.4
Derivative assets | 33.0 | 10.1
Deferred compensation plan assets | 17.5 | 12.1
Total financial assets | 13,254.6 | 12,025.0
Financial liabilities: |  |
Total deposits, excluding time deposits | 10,264.6 | 9,363.7
Time deposits | 1,535.0 | 1,317.0
Securities sold under repurchase agreements | 636.9 | 712.4
Accrued interest payable | 12.3 | 7.8
Long-term debt | 13.9 | 15.8
Subordinated debentures held by subsidiary trusts | 86.9 | 86.9
Derivative liabilities | 30.8 | 9.4
Deferred compensation plan liabilities | 17.5 | 12.1
Total financial liabilities | 12,597.9 | 11,525.1
Estimated Fair Value |  |
Financial assets: |  |
Cash and cash equivalents | 1,269.6 | 822.0
Investment debt securities available-for-sale | 2,732.2 | 2,270.7
Investment debt securities held-to-maturity | 97.2 | 400.7
Accrued interest receivable | 51.1 | 44.9
Mortgage servicing rights, net | 32.1 | 42.4
Loans held for sale | 108.9 | 33.3
Net loans held for investment | 8,953.4 | 8,439.7
Derivative assets | 33.0 | 10.1
Deferred compensation plan assets | 17.5 | 12.1
Total financial assets | 13,295.0 | 12,075.9
Financial liabilities: |  |
Total deposits, excluding time deposits | 10,264.6 | 9,363.7
Time deposits | 1,530.9 | 1,299.0
Securities sold under repurchase agreements | 636.9 | 712.4
Accrued interest payable | 12.3 | 7.8
Long-term debt | 11.3 | 13.0
Subordinated debentures held by subsidiary trusts | 77.9 | 84.9
Derivative liabilities | 30.8 | 9.4
Deferred compensation plan liabilities | 17.5 | 12.1
Total financial liabilities | 12,582.2 | 11,502.3
Quoted Prices in Active Markets for Identical Assets (Level 1) | Estimated Fair Value |  |
Financial assets: |  |
Cash and cash equivalents | 1,269.6 | 822.0
Investment debt securities available-for-sale | 0.0 | 0.0
Investment debt securities held-to-maturity | 0.0 | 0.0
Accrued interest receivable | 0.0 | 0.0
Mortgage servicing rights, net | 0.0 | 0.0
Loans held for sale | 0.0 | 0.0
Net loans held for investment | 0.0 | 0.0
Derivative assets | 0.0 | 0.0
Deferred compensation plan assets | 0.0 | 0.0
Total financial assets | 1,269.6 | 822.0
Financial liabilities: |  |
Total deposits, excluding time deposits | 10,264.6 | 9,363.7
Time deposits | 0.0 | 0.0
Securities sold under repurchase agreements | 0.0 | 0.0
Accrued interest payable | 0.0 | 0.0
Long-term debt | 0.0 | 0.0
Subordinated debentures held by subsidiary trusts | 0.0 | 0.0
Derivative liabilities | 0.0 | 0.0
Deferred compensation plan liabilities | 0.0 | 0.0
Total financial liabilities | 10,264.6 | 9,363.7
Significant Other Observable Inputs (Level 2) | Estimated Fair Value |  |
Financial assets: |  |
Cash and cash equivalents | 0.0 | 0.0
Investment debt securities available-for-sale | 2,732.2 | 2,270.7
Investment debt securities held-to-maturity | 97.2 | 400.7
Accrued interest receivable | 51.1 | 44.9
Mortgage servicing rights, net | 32.1 | 42.4
Loans held for sale | 108.9 | 33.3
Net loans held for investment | 8,926.2 | 8,415.6
Derivative assets | 33.0 | 10.1
Deferred compensation plan assets | 17.5 | 12.1
Total financial assets | 11,998.2 | 11,229.8
Financial liabilities: |  |
Total deposits, excluding time deposits | 0.0 | 0.0
Time deposits | 1,530.9 | 1,299.0
Securities sold under repurchase agreements | 636.9 | 712.4
Accrued interest payable | 12.3 | 7.8
Long-term debt | 11.3 | 13.0
Subordinated debentures held by subsidiary trusts | 77.9 | 84.9
Derivative liabilities | 30.8 | 9.4
Deferred compensation plan liabilities | 17.5 | 12.1
Total financial liabilities | 2,317.6 | 2,138.6
Significant Unobservable Inputs (Level 3) | Estimated Fair Value |  |
Financial assets: |  |
Cash and cash equivalents | 0.0 | 0.0
Investment debt securities available-for-sale | 0.0 | 0.0
Investment debt securities held-to-maturity | 0.0 | 0.0
Accrued interest receivable | 0.0 | 0.0
Mortgage servicing rights, net | 0.0 | 0.0
Loans held for sale | 0.0 | 0.0
Net loans held for investment | 27.2 | 24.1
Derivative assets | 0.0 | 0.0
Deferred compensation plan assets | 0.0 | 0.0
Total financial assets | 27.2 | 24.1
Financial liabilities: |  |
Total deposits, excluding time deposits | 0.0 | 0.0
Time deposits | 0.0 | 0.0
Securities sold under repurchase agreements | 0.0 | 0.0
Accrued interest payable | 0.0 | 0.0
Long-term debt | 0.0 | 0.0
Subordinated debentures held by subsidiary trusts | 0.0 | 0.0
Derivative liabilities | 0.0 | 0.0
Deferred compensation plan liabilities | 0.0 | 0.0
Total financial liabilities | $ 0.0 | $ 0.0

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