Significant Accounting Policies - Basis of Presentation (Details) - USD ($)	Mar. 31, 2019	Dec. 31, 2018
Variable Interest Entity [Line Items]
Investments in firm-sponsored vehicles where we are not primary beneficiary	$ 500,000	$ 2,400,000
Maximum loss exposure	800,000	2,700,000
Pzena International Value Service, a series of Pzena Investment Management International, LLC
Variable Interest Entity [Line Items]
Equity method investment, assets	3,800,000
VIEs that are not consolidated
Variable Interest Entity [Line Items]
Equity method investment, assets	$ 253,600,000	$ 205,400,000

The amount of assets reported by an equity method investment of the entity.

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The reporting entity's maximum amount of exposure to loss as a result of its involvement with the Variable Interest Entity (VIE).

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