Investments (Summary of Investments) (Details) - USD ($) $ in Thousands	Sep. 30, 2016	Dec. 31, 2015
Summary of Investment Holdings [Line Items]
Investments owned	$ 694,492	$ 669,800
Long-term incentive compensation obligations	67,507	78,154
Seed capital
Summary of Investment Holdings [Line Items]
Investments owned	401,000	478,000
Consolidated private equity fund
Summary of Investment Holdings [Line Items]
Investments owned	0	23,897
Private equity
Summary of Investment Holdings [Line Items]
Investments owned	36,412	48,761
Investments held by consolidated VIEs
Summary of Investment Holdings [Line Items]
Investments owned	205,104	0
Time deposits
Summary of Investment Holdings [Line Items]
Investments owned	35,311	9,906
Available-for-sale
Summary of Investment Holdings [Line Items]
Investments owned	228	364
Trading | Long-term incentive compensation-related
Summary of Investment Holdings [Line Items]
Investments owned	50,095	59,150
Trading | U.S. Treasury Bills
Summary of Investment Holdings [Line Items]
Investments owned	29,922	24,942
Trading | Seed capital
Summary of Investment Holdings [Line Items]
Investments owned	269,078	406,322
Trading | Equities
Summary of Investment Holdings [Line Items]
Investments owned	16,793	43,584
Trading | Exchange-traded options
Summary of Investment Holdings [Line Items]
Investments owned	3,549	5,910
Investments in limited partnership hedge funds | Long-term incentive compensation-related
Summary of Investment Holdings [Line Items]
Investments owned	17,412	19,004
Investments in limited partnership hedge funds | Seed capital
Summary of Investment Holdings [Line Items]
Investments owned	22,850	20,082
Other
Summary of Investment Holdings [Line Items]
Investments owned	$ 7,738	$ 7,878