Investments - Summary of Investments (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Summary of Investment Holdings [Line Items]
Investments owned	$ 266,794	$ 714,344
Seed capital
Summary of Investment Holdings [Line Items]
Investments owned	358,100	391,600
U.S. Treasury Bills
Summary of Investment Holdings [Line Items]
Investments owned	0	392,424
Equity securities: | Long-term incentive compensation-related
Summary of Investment Holdings [Line Items]
Investments owned	36,665	38,883
Equity securities: | Seed capital
Summary of Investment Holdings [Line Items]
Investments owned	70,464	105,951
Equity securities: | Other
Summary of Investment Holdings [Line Items]
Investments owned	73,202	73,409
Exchange-traded options
Summary of Investment Holdings [Line Items]
Investments owned	6,931	2,568
Investments in limited partnership hedge funds: | Long-term incentive compensation-related
Summary of Investment Holdings [Line Items]
Investments owned	14,237	13,546
Investments in limited partnership hedge funds: | Seed capital
Summary of Investment Holdings [Line Items]
Investments owned	33,124	67,153
Time deposits
Summary of Investment Holdings [Line Items]
Investments owned	18,281	8,783
Other
Summary of Investment Holdings [Line Items]
Investments owned	$ 13,890	$ 11,627