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Investment Securities - Significant Unobservable Inputs (Details) $ in Millions | 9 Months Ended | 12 Months Ended
--- | --- | ---
Sep. 30, 2022 USD ($) | Sep. 30, 2021 USD ($) | Dec. 31, 2021 USD ($)
Quantitative information for Level 3 Fair Value Measurements Assets |  |  |
Investments in trading securities | $ 97.9 | $ 141.6 |
Kudu investments | Discount rate | Standard Poors NR Rating |  |  |
Quantitative information for Level 3 Fair Value Measurements Assets |  |  |
Fair value, pretax discount rate | 0.20 |  | 0.20
Cash flow exit multiple, pretax | 9.7 |  | 10
TIG Advisors, TK Partners, Third Eye Capital Management, Douglass Winthrop Advisors, Granahan Investment Management and Radcliffe Capital Management | Kudu |  |  |
Quantitative information for Level 3 Fair Value Measurements Assets |  |  |
Investments in trading securities |  |  | $ 223.4
Level 3 | Other long-term investments | Standard Poors NR Rating |  |  |
Quantitative information for Level 3 Fair Value Measurements Assets |  |  |
Assets, fair value | $ 42.9 |  | 46.7
Level 3 | Kudu investments | Standard Poors NR Rating | Discounted cash flow |  |  |
Quantitative information for Level 3 Fair Value Measurements Assets |  |  |
Assets, fair value | 813.2 |  | 669.5
Level 3 | Kudu investments | Standard Poors NR Rating | Probability weighted expected return method |  |  |
Quantitative information for Level 3 Fair Value Measurements Assets |  |  |
Assets, fair value | $ 312.4 |  | $ 78.8
Level 3 | Kudu investments | Discount rate | Standard Poors NR Rating | Minimum |  |  |
Quantitative information for Level 3 Fair Value Measurements Assets |  |  |
Fair value, discount rate | 17.00% |  | 18.00%
Level 3 | Kudu investments | Discount rate | Standard Poors NR Rating | Maximum |  |  |
Quantitative information for Level 3 Fair Value Measurements Assets |  |  |
Fair value, discount rate | 24.00% |  | 23.00%
Level 3 | Kudu investments | Terminal Multiple | Standard Poors NR Rating | Minimum |  |  |
Quantitative information for Level 3 Fair Value Measurements Assets |  |  |
Terminal cash flow exit multiple | 7 |  | 7
Level 3 | Kudu investments | Terminal Multiple | Standard Poors NR Rating | Maximum |  |  |
Quantitative information for Level 3 Fair Value Measurements Assets |  |  |
Terminal cash flow exit multiple | 16 |  | 13
Level 3 | PassportCard/DavidShield | Standard Poors NR Rating | Discounted cash flow |  |  |
Quantitative information for Level 3 Fair Value Measurements Assets |  |  |
Assets, fair value | $ 132.0 |  | $ 120.0
Level 3 | PassportCard/DavidShield | Discount rate | Standard Poors NR Rating |  |  |
Quantitative information for Level 3 Fair Value Measurements Assets |  |  |
Fair value, discount rate | 24.00% |  | 23.00%
Level 3 | PassportCard/DavidShield | Measurement Input, Long-term Revenue Growth Rate | Standard Poors NR Rating |  |  |
Quantitative information for Level 3 Fair Value Measurements Assets |  |  |
Terminal revenue growth rate | 4.00% |  | 4.00%
Level 3 | Elementum Holdings, L.P. | Standard Poors NR Rating | Discounted cash flow |  |  |
Quantitative information for Level 3 Fair Value Measurements Assets |  |  |
Assets, fair value | $ 45.0 |  | $ 45.0
Level 3 | Elementum Holdings, L.P. | Discount rate | Standard Poors NR Rating |  |  |
Quantitative information for Level 3 Fair Value Measurements Assets |  |  |
Fair value, discount rate | 18.00% |  | 17.00%
Level 3 | Elementum Holdings, L.P. | Measurement Input, Long-term Revenue Growth Rate | Standard Poors NR Rating |  |  |
Quantitative information for Level 3 Fair Value Measurements Assets |  |  |
Terminal revenue growth rate | 4.00% |  | 4.00%
Level 3 | Private debt investments | Standard Poors NR Rating | Discounted cash flow |  |  |
Quantitative information for Level 3 Fair Value Measurements Assets |  |  |
Assets, fair value | $ 11.0 |  | $ 9.4
Level 3 | Private debt investments | Discount rate | Standard Poors NR Rating |  |  |
Quantitative information for Level 3 Fair Value Measurements Assets |  |  |
Fair value, discount rate | 10.00% |  | 8.00%
Level 3 | Gramercy Funds Management, GenTrust, EC Management Services, and TK Partners | Standard Poors NR Rating | Discounted cash flow |  |  |
Quantitative information for Level 3 Fair Value Measurements Assets |  |  |
Investments in trading securities | $ 97.9 |  |

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