Investments - Summary of Investments (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Summary of Investment Holdings [Line Items]
Investments owned	$ 294,666	$ 266,794
Long-term incentive compensation obligations	53,600	50,900
Seed capital
Summary of Investment Holdings [Line Items]
Investments owned	342,000	358,100
Equity securities | Long-term incentive compensation-related
Summary of Investment Holdings [Line Items]
Investments owned	30,064	36,665
Equity securities | Seed capital
Summary of Investment Holdings [Line Items]
Investments owned	128,363	70,464
Equity securities | Other
Summary of Investment Holdings [Line Items]
Investments owned	53,117	73,202
Exchange-traded options
Summary of Investment Holdings [Line Items]
Investments owned	12,151	6,931
Investments in limited partnership hedge funds | Long-term incentive compensation-related
Summary of Investment Holdings [Line Items]
Investments owned	23,547	14,237
Investments in limited partnership hedge funds | Seed capital
Summary of Investment Holdings [Line Items]
Investments owned	16,463	33,124
Time deposits
Summary of Investment Holdings [Line Items]
Investments owned	17,418	18,281
Other
Summary of Investment Holdings [Line Items]
Investments owned	$ 13,543	$ 13,890