Redeemable Non-Controlling Interests in Consolidated Subsidiaries and Funds (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Noncontrolling Interest [Line Items]
Redeemable non-controlling interests in consolidated subsidiaries and funds	$ 86,076				$ 85,814				$ 86,076	$ 85,814
Net income (loss) attributable to redeemable non-controlling interests in consolidated subsidiaries and funds	2,155	4,006	5,216	4,187	2,684	4,759	2,255	3,495	15,564	13,193	(72)
Operating Entities
Noncontrolling Interest [Line Items]
Redeemable non-controlling interests in consolidated subsidiaries and funds	9,619				12,009				9,619	12,009
Net income (loss) attributable to redeemable non-controlling interests in consolidated subsidiaries and funds									10,094	10,461	301
Consolidated Funds
Noncontrolling Interest [Line Items]
Redeemable non-controlling interests in consolidated subsidiaries and funds	76,457				73,805				76,457	73,805
Net income (loss) attributable to redeemable non-controlling interests in consolidated subsidiaries and funds									$ 5,470	$ 2,732	$ (373)