Investments in Affiliates - Investment Fund Affiliates (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Schedule of Equity Method Investments [Line Items]
Investments in affiliates		$ 2,177,645	$ 1,708,899
Equity in net income (loss) in operating affiliates		115,155	118,060	$ 203,034
Investment fund affiliates
Schedule of Equity Method Investments [Line Items]
Investments in affiliates		1,674,925	1,386,837
Equity in net income (loss) in operating affiliates		$ 70,758	$ 73,320
Ownership percentage remaining		5.50%	5.80%
Combined funds/ estimated total net assets	[1]	$ 30,600,053	$ 24,101,796
Investment fund affiliates | Hedge funds
Schedule of Equity Method Investments [Line Items]
Investments in affiliates		1,317,375	1,084,198
Equity in net income (loss) in operating affiliates		$ 41,670	$ 42,668
Ownership percentage remaining		4.80%	5.20%
Combined funds/ estimated total net assets	[1]	$ 27,281,980	$ 20,906,592
Investment fund affiliates | Arbitrage
Schedule of Equity Method Investments [Line Items]
Investments in affiliates		165,633	190,016
Equity in net income (loss) in operating affiliates		$ 965	$ 612
Ownership percentage remaining		12.30%	8.60%
Combined funds/ estimated total net assets	[1]	$ 1,343,655	$ 2,202,112
Investment fund affiliates | Directional
Schedule of Equity Method Investments [Line Items]
Investments in affiliates		672,934	551,262
Equity in net income (loss) in operating affiliates		$ 1,480	$ 31,012
Ownership percentage remaining		7.40%	7.20%
Combined funds/ estimated total net assets	[1]	$ 9,039,159	$ 7,643,134
Investment fund affiliates | Event driven
Schedule of Equity Method Investments [Line Items]
Investments in affiliates	[2]	297,836	285,823
Equity in net income (loss) in operating affiliates	[2]	$ 9,676	$ 5,592
Ownership percentage remaining	[2]	2.60%	3.00%
Combined funds/ estimated total net assets	[1],[2]	$ 11,341,870	$ 9,460,387
Investment fund affiliates | Multi-style
Schedule of Equity Method Investments [Line Items]
Investments in affiliates		180,972	57,097
Equity in net income (loss) in operating affiliates		$ 29,549	$ 5,452
Ownership percentage remaining		3.30%	3.60%
Combined funds/ estimated total net assets	[1]	$ 5,557,296	$ 1,600,959
Investment fund affiliates | Private investment funds
Schedule of Equity Method Investments [Line Items]
Investments in affiliates		357,550	302,639
Equity in net income (loss) in operating affiliates		$ 29,088	$ 30,652
Ownership percentage remaining		10.80%	9.50%
Combined funds/ estimated total net assets	[1]	$ 3,318,073	$ 3,195,204

[1] Total estimated net assets are generally as at November 30 for hedge fund affiliates and September 30 for private investment fund affiliates.

[2] The Company accounts for its investment in certain funds using the equity method where the Company has significant influence over the related investment management company even though the ownership percentage is less than three percent.