Redeemable Non-Controlling Interests in Consolidated Subsidiaries and Funds (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Noncontrolling Interest [Line Items]
Redeemable non-controlling interests in consolidated subsidiaries and funds	$ 284,780				$ 440,604				$ 284,780	$ 440,604
Net income (loss) attributable to redeemable non-controlling interests in consolidated subsidiaries and funds	(655)	$ 5,290	$ 24,607	$ 11,156	(11,621)	$ 5,162	$ 21,145	$ 9,105	40,398	23,791	$ 6,882
Operating Entities
Noncontrolling Interest [Line Items]
Redeemable non-controlling interests in consolidated subsidiaries and funds	10,434				6,113				10,434	6,113
Net income (loss) attributable to redeemable non-controlling interests in consolidated subsidiaries and funds									6,515	2,353	3,717
Consolidated Funds
Noncontrolling Interest [Line Items]
Redeemable non-controlling interests in consolidated subsidiaries and funds	$ 274,346				$ 434,491				274,346	434,491
Net income (loss) attributable to redeemable non-controlling interests in consolidated subsidiaries and funds									$ 33,883	$ 21,438	$ 3,165