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Equity Method Investments in Affiliates - Additional Information (Details) - USD ($) $ in Millions | 3 Months Ended | 6 Months Ended
--- | --- | ---
Jun. 30, 2020 | Mar. 31, 2020 | Jun. 30, 2019 | Mar. 31, 2019 | Jun. 30, 2020 | Jun. 30, 2019
Estimated Future Amortization Expense of Finite-Lived Intangibles |  |  |  |  |  |
Net income | $ 63.5 |  | $ 180.2 |  | $ 103.4 | $ 47.2
Acquired Client Relationships |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |
Amortization expense during the period |  |  |  |  | 55.7 |
Estimated Future Amortization Expense of Finite-Lived Intangibles |  |  |  |  |  |
Finite-lived intangible, future amortization expense in 2020 | 60.0 |  |  |  | 60.0 |
Finite-lived intangible, future amortization expense in 2021 | 30.0 |  |  |  | 30.0 |
Finite-lived intangible, future amortization expense in 2022 | 30.0 |  |  |  | 30.0 |
Finite-lived intangible, future amortization expense in 2023 | 30.0 |  |  |  | 30.0 |
Finite-lived intangible, future amortization expense in 2024 | 20.0 |  |  |  | 20.0 |
Equity Method Investee |  |  |  |  |  |
Estimated Future Amortization Expense of Finite-Lived Intangibles |  |  |  |  |  |
Impairment expense |  | $ 140.0 |  | $ 415.0 |  |
Average projected growth rate period |  | 5 years |  | 5 years |  |
Average projected growth rate |  | (2.00%) |  | (13.00%) |  |
Discount rate for assets based fees |  | 11.00% |  | 11.00% |  |
Discount rate for performance fees |  | 20.00% |  | 20.00% |  |
Market participant tax rate |  | 25.00% |  | 25.00% |  |
Equity Method Investee | Acquired Client Relationships |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |
Amortization expense during the period | 36.9 |  | 38.9 |  | 76.2 | 62.1
Estimated Future Amortization Expense of Finite-Lived Intangibles |  |  |  |  |  |
Finite-lived intangible, future amortization expense in 2020 | 150.0 |  |  |  | 150.0 |
Finite-lived intangible, future amortization expense in 2021 | 120.0 |  |  |  | 120.0 |
Finite-lived intangible, future amortization expense in 2022 | 50.0 |  |  |  | 50.0 |
Finite-lived intangible, future amortization expense in 2023 | 50.0 |  |  |  | 50.0 |
Finite-lived intangible, future amortization expense in 2024 | 50.0 |  |  |  | 50.0 |
Certain Affiliates |  |  |  |  |  |
Estimated Future Amortization Expense of Finite-Lived Intangibles |  |  |  |  |  |
Revenues | 460.1 |  | 519.9 |  | 1,165.3 | 1,168.2
Net income | $ 128.5 |  | $ 238.5 |  | $ 555.6 | $ 580.7

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