Condensed Consolidated Statements of Cash Flows (USD $) In Thousands, unless otherwise specified	6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011
Cash flows from operating activities:
Net income (loss)	$ (4,144)	$ 23,375
Adjustments to reconcile net income (loss) to net cash provided by / (used in) operating activities:
Bargain purchase gain	0	(22,244)
Depreciation and amortization	4,518	4,069
Share-based compensation	13,526	14,086
Deferred rent obligations	(952)	(569)
Purchases of securities owned, at fair value	(3,318,650)	(5,053,676)
Proceeds from sales of securities owned, at fair value	3,232,262	4,834,296
Proceeds from sales of securities sold, not yet purchased, at fair value	2,497,536	2,485,115
Payments to cover securities sold, not yet purchased, at fair value	(2,403,844)	(2,435,760)
Net (gains) losses on securities, derivatives and other investments	(24,157)	(13,509)
Consolidated Funds
Purchases of securities owned, at fair value, Consolidated Funds	(163,715)	(245,778)
Proceeds from sales of securities owned, at fair value, Consolidated Funds	167,812	248,297
Purchases of other investments, Consolidated Funds	(7,122)	(11,101)
Proceeds from sales of other investments, Consolidated Funds	11,986	87,963
Net realized and unrealized (gains) losses on investments and other transactions, Consolidated Funds	(4,883)	(5,373)
(Increase) decrease in operating assets:
Cash acquired upon transaction	0	117,496
Cash collateral pledged	528	(41)
Securities owned, at fair value, held at broker dealer	23,444	(73,150)
Receivable from brokers	46,808	64,704
Fees receivable	4,258	9,246
Due from related parties	(447)	136
Other assets	3,301	(8,765)
Consolidated Funds
Cash and cash equivalents, Consolidated Funds	926	6,421
Other assets, Consolidated Funds	1,036	449
Increase (decrease) in operating liabilities:
Securities sold, not yet purchased, at fair value, held at broker dealer	(14,181)	28,189
Payable to brokers	13,434	154,035
Compensation payable	(50,540)	(52,799)
Fees payable	490	(3,338)
Due to related parties	(1,143)	(6,630)
Accounts payable, accrued expenses and other liabilities	(5,406)	3,908
Consolidated Funds
Due to related parties, Consolidated Funds	25	0
Accounts payable, accrued expenses and other liabilities, Consolidated Funds	324	(1,165)
Net cash provided by / (used in) operating activities	23,924	147,615
Cash flows from investing activities:
Securities purchased under agreement to resell	(58,313)	20,423
Purchases of other investments	(3,889)	(40,650)
Purchase of business, net of cash acquired (See Note 2)	(10,062)	0
Proceeds from sales of other investments	7,429	39,567
Purchase of fixed assets	(1,084)	(4,263)
Net cash provided by / (used in) investing activities	(65,919)	15,077
Cash flows from financing activities:
Securities sold under agreement to repurchase	6,175	(22,726)
Borrowings on short-term borrowings and other debt	0	493
Repayments on short-term borrowings and other debt	(794)	(25,608)
Purchase of treasury stock	(4,516)	0
Capital withdrawals to noncontrolling interests in operating entities	(2,267)	(2,009)
Consolidated Funds
Capital contributions by non-controlling interests in Consolidated Funds	0	4,038
Capital withdrawals to non-controlling interests in Consolidated Funds	(5,409)	(43,059)
Net cash provided by / (used in) financing activities	(6,811)	(88,871)
Change in cash and cash equivalents	(48,806)	73,821
Cash and cash equivalents at beginning of year	128,875	36,354
Cash and cash equivalents at end of year	80,069	110,175
Supplemental non-cash information
Purchase of treasury stock, at cost, upon close of acquisition (see Note 2)	0	1,906
Net assets acquired upon acquisition (net of cash) (See Note 2)	0	58,486
Non compete agreements and covenants with limiting conditions acquired (see Note 2)	0	2,310
Common stock issuance upon close of acquisition (see Note 2)	0	156,048
Purchase of treasury stock, at cost, through net settlement (See Note 15)	1,841	0
Net assets of consolidated entities	18,521	3,470
Net assets of deconsolidated entities	$ 17,104	$ 0