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Goodwill and Acquired Client Relationships - Additional Information (Details) - USD ($) | 3 Months Ended | 9 Months Ended
--- | --- | ---
Sep. 30, 2018 | Sep. 30, 2017 | Sep. 30, 2018 | Sep. 30, 2017
Intangible Assets |  |  |  |
Goodwill impairment |  |  | $ 0 |
Amortization and impairment expenses of intangible assets | $ 30,100,000 | $ 21,200,000 | 76,500,000 | $ 65,100,000
Acquired Client Relationships |  |  |  |
Estimated Future Amortization Expense of Finite-Lived Intangibles |  |  |  |
Finite-lived intangible, future amortization expense in 2018 | 100,000,000 |  | 100,000,000 |
Finite-lived intangible, future amortization expense in 2019 | 90,000,000 |  | 90,000,000 |
Finite-lived intangible, future amortization expense in 2020 | 60,000,000 |  | 60,000,000 |
Finite-lived intangible, future amortization expense in 2021 | 35,000,000 |  | 35,000,000 |
Finite-lived intangible, future amortization expense in 2022 | 35,000,000 |  | 35,000,000 |
Acquired Client Relationships | Intangible amortization and impairments |  |  |  |
Intangible Assets |  |  |  |
Amortization and impairment expenses of intangible assets | $ 30,100,000 | $ 21,200,000 | $ 76,500,000 | $ 65,100,000

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