Redeemable Non-Controlling Interests in Consolidated Subsidiaries (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Noncontrolling Interest [Line Items]
Redeemable non-controlling interests in consolidated subsidiaries	$ 85,703				$ 104,587				$ 85,703	$ 104,587
Net income (loss) attributable to redeemable non-controlling interests in consolidated subsidiaries	1,154	(1,033)	(2,434)	2,241	3,354	(783)	2,458	798	(72)	5,827	13,727
Operating Companies
Noncontrolling Interest [Line Items]
Redeemable non-controlling interests in consolidated subsidiaries	4,106				6,472				4,106	6,472
Net income (loss) attributable to redeemable non-controlling interests in consolidated subsidiaries									301	7,002	1,759
Consolidated Funds
Noncontrolling Interest [Line Items]
Redeemable non-controlling interests in consolidated subsidiaries	81,597				98,115				81,597	98,115
Net income (loss) attributable to redeemable non-controlling interests in consolidated subsidiaries									$ (373)	$ (1,175)	$ 11,968