Redeemable Non-Controlling Interests in Consolidated Subsidiaries and Funds (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Noncontrolling Interest [Line Items]
Redeemable non-controlling interests in consolidated subsidiaries and funds	$ 440,604				$ 379,205				$ 440,604	$ 379,205
Net income (loss) attributable to redeemable non-controlling interests in consolidated subsidiaries and funds	(11,621)	$ 5,162	$ 21,145	$ 9,105	9,406	$ 18,478	$ (16,705)	$ (4,297)	23,791	6,882	$ 15,246
Operating Entities
Noncontrolling Interest [Line Items]
Redeemable non-controlling interests in consolidated subsidiaries and funds	6,113				7,638				6,113	7,638
Net income (loss) attributable to redeemable non-controlling interests in consolidated subsidiaries and funds									2,353	3,717	9,503
Consolidated Funds
Noncontrolling Interest [Line Items]
Redeemable non-controlling interests in consolidated subsidiaries and funds	$ 434,491				$ 371,567				434,491	371,567
Net income (loss) attributable to redeemable non-controlling interests in consolidated subsidiaries and funds									$ 21,438	$ 3,165	$ 5,743