Investments - Summary of Investments (Details) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Summary of Investment Holdings [Line Items]
Investments owned	$ 669,800	$ 763,475
Long-term incentive compensation-related	78,154	98,779
Available-for-sale Securities [Member]
Summary of Investment Holdings [Line Items]
Investments owned	364	6,172
Other Investment [Member]
Summary of Investment Holdings [Line Items]
Investments owned	17,784	11,497
Long-term Incentive Compensation-Related [Member] | Trading Securities [Member]
Summary of Investment Holdings [Line Items]
Investments owned	59,150	74,095
Long-term Incentive Compensation-Related [Member] | Investments In Limited Partnership Hedge Funds [Member]
Summary of Investment Holdings [Line Items]
Investments owned	19,004	24,684
US Treasury Bill Securities [Member] | Trading Securities [Member]
Summary of Investment Holdings [Line Items]
Investments owned	24,942	28,982
Seed Capital [Member] | Trading Securities [Member]
Summary of Investment Holdings [Line Items]
Investments owned	406,322	400,746
Seed Capital [Member] | Investments In Limited Partnership Hedge Funds [Member]
Summary of Investment Holdings [Line Items]
Investments owned	20,082	33,951
Equities [Member] | Trading Securities [Member]
Summary of Investment Holdings [Line Items]
Investments owned	43,584	79,720
Exchange Traded Options [Member] | Trading Securities [Member]
Summary of Investment Holdings [Line Items]
Investments owned	5,910	22,290
Consolidated Private Equity Fund [Member]
Summary of Investment Holdings [Line Items]
Investments owned	23,897	32,604
Private Equity [Member]
Summary of Investment Holdings [Line Items]
Investments owned	$ 48,761	$ 48,734