Investments - Additional Information (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Investment Holdings [Line Items]
Long-term incentive compensation-related	$ 52,429	$ 66,034
Investments owned	714,344	443,589
Seed capital
Investment Holdings [Line Items]
Seed investment in deconsolidated fund	42,500
Investments owned	391,600	523,200
Private equity
Investment Holdings [Line Items]
Investments owned	0	38,186
Private equity \| Seed capital
Investment Holdings [Line Items]
Investments owned		37,200
Investments in limited partnership hedge funds \| Seed capital
Investment Holdings [Line Items]
Increase in seed capital in limited partnership hedge funds	44,200
Investments owned	$ 67,153	$ 22,923

Value of the investment at close of period. For schedules of investments that are categorized, the value would be aggregated by category. For investment in and advances to affiliates, if operations of any controlled companies are different in character from those of the company, group such affiliates within divisions and by type of activities.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
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Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
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Reference 5: http://fasb.org/us-gaap/role/ref/legacyRef
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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant