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Equity Method Investments in Affiliates - Additional Information (Details) - USD ($) $ in Millions | 3 Months Ended | 9 Months Ended
--- | --- | ---
Sep. 30, 2017 | Sep. 30, 2016 | Sep. 30, 2017 | Sep. 30, 2016
Schedule of Equity Method Investments [Line Items] |  |  |  |
Amortization expense during the period | $ 21.2 | $ 26.9 | $ 65.1 | $ 82.2
Acquired Client Relationships |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |
Weighted average client-acquired relationships |  |  | 12 years |
Finite-lived intangible, future amortization expense, next twelve months | 85.0 |  | $ 85.0 |
Finite-lived intangible, future amortization expense, year 2 | 85.0 |  | 85.0 |
Finite-lived intangible, future amortization expense, year 3 | 85.0 |  | 85.0 |
Finite-lived intangible, future amortization expense, year 4 | 50.0 |  | 50.0 |
Finite-lived intangible, future amortization expense, year 5 | 30.0 |  | 30.0 |
Equity Method Investee |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |
Revenue from equity method investments | 301.8 | 230.2 | 826.6 | 658.6
Net income from equity method investments | 178.3 | 126.4 | $ 471.3 | 361.0
Equity Method Investee | Acquired Client Relationships |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |
Weighted average client-acquired relationships |  |  | 10 years |
Amortization expense during the period | 25.9 | 14.0 | $ 71.7 | 43.0
Finite-lived intangible, future amortization expense, next twelve months | 100.0 |  | 100.0 |
Finite-lived intangible, future amortization expense, year 2 | 100.0 |  | 100.0 |
Finite-lived intangible, future amortization expense, year 3 | 80.0 |  | 80.0 |
Finite-lived intangible, future amortization expense, year 4 | 80.0 |  | 80.0 |
Finite-lived intangible, future amortization expense, year 5 | 80.0 |  | 80.0 |
Systematica Investment LP and Baring Private Equity Asia | Equity Method Investee | Acquired Client Relationships |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |
Amortization expense during the period | $ 15.5 | $ 3.7 | $ 33.9 | $ 11.2

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