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Equity Method Investments in Affiliates - Additional Information (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Schedule of Equity Method Investments [Line Items]
Amortization expense during the period	$ 29.6	$ 23.2
Estimated Future Amortization Expense of Finite-Lived Intangibles
Impairment recognized on equity method investment	$ 415.0
Fair value assumptions, period of projected annual based fee margin growth rate	5 years
Fair value assumptions, projected annual based fee margin growth rate	(13.00%)
Fair value assumptions, discount rate for asset based fees	11.00%
Fair value assumptions, discount rate for performance based fees	20.00%
Fair value assumptions, market participant tax rate	25.00%
Acquired Client Relationships
Estimated Future Amortization Expense of Finite-Lived Intangibles
Finite-lived intangible, future amortization expense in 2019	$ 120.0
Finite-lived intangible, future amortization expense in 2020	90.0
Finite-lived intangible, future amortization expense in 2021	65.0
Finite-lived intangible, future amortization expense in 2022	65.0
Finite-lived intangible, future amortization expense in 2023	65.0
Equity Method Investee | Acquired Client Relationships
Schedule of Equity Method Investments [Line Items]
Amortization expense during the period	23.2	$ 30.0
Estimated Future Amortization Expense of Finite-Lived Intangibles
Finite-lived intangible, future amortization expense in 2019	90.0
Finite-lived intangible, future amortization expense in 2020	90.0
Finite-lived intangible, future amortization expense in 2021	85.0
Finite-lived intangible, future amortization expense in 2022	85.0
Finite-lived intangible, future amortization expense in 2023	$ 85.0

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