Goodwill and Acquired Client Relationships - Additional Information (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Intangible Assets
Amortization and impairment expenses of intangible assets	$ 21.2	$ 23.2	$ 50.9	$ 46.4
Acquired Client Relationships
Intangible Assets
Amortization and impairment expenses of intangible assets			50.9
Estimated Future Amortization Expense of Finite-Lived Intangibles
Finite-lived intangible, future amortization expense in 2019	100.0		100.0
Finite-lived intangible, future amortization expense in 2020	75.0		75.0
Finite-lived intangible, future amortization expense in 2021	50.0		50.0
Finite-lived intangible, future amortization expense in 2022	50.0		50.0
Finite-lived intangible, future amortization expense in 2023	50.0		50.0
Acquired Client Relationships \| Intangible amortization and impairments
Intangible Assets
Amortization and impairment expenses of intangible assets	$ 21.2	$ 23.2	$ 50.9	$ 46.4

-- None. No documentation exists for this element. --

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The aggregate expense charged against earnings to allocate the cost of intangible assets (nonphysical assets not used in production) in a systematic and rational manner to the periods expected to benefit from such assets. As a noncash expense, this element is added back to net income when calculating cash provided by or used in operations using the indirect method.

+ References

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Amount of amortization expense for assets, excluding financial assets and goodwill, lacking physical substance with a finite life expected to be recognized during the next fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

+ References

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-Publisher FASB
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-Topic 350
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-Section 50
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- Definition

Amount of amortization expense for assets, excluding financial assets and goodwill, lacking physical substance with a finite life expected to be recognized during the fifth fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

+ References

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Amount of amortization expense for assets, excluding financial assets and goodwill, lacking physical substance with a finite life expected to be recognized during the fourth fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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Amount of amortization expense for assets, excluding financial assets and goodwill, lacking physical substance with a finite life expected to be recognized during the third fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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Amount of amortization expense for assets, excluding financial assets and goodwill, lacking physical substance with a finite life expected to be recognized during the second fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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