Redeemable Non-Controlling Interests in Consolidated Subsidiaries and Funds (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Noncontrolling Interest [Line Items]
Redeemable non-controlling interests in consolidated subsidiaries and funds	$ 203,212		$ 203,212		$ 440,604
Net income (loss) attributable to redeemable non-controlling interests in consolidated subsidiaries and funds	5,290	$ 5,162	41,053	$ 35,412
Operating Entities
Noncontrolling Interest [Line Items]
Redeemable non-controlling interests in consolidated subsidiaries and funds	11,069		11,069		6,113
Net income (loss) attributable to redeemable non-controlling interests in consolidated subsidiaries and funds	2,486	(266)	6,060	1,457
Consolidated Funds
Noncontrolling Interest [Line Items]
Redeemable non-controlling interests in consolidated subsidiaries and funds	192,143		192,143		$ 434,491
Net income (loss) attributable to redeemable non-controlling interests in consolidated subsidiaries and funds	$ 2,804	$ 5,428	$ 34,993	$ 33,955