Condensed Consolidated Statements of Cash Flows (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011
Cash flows from operating activities:
Net income (loss)	$ 6,236	$ 880
Adjustments to reconcile net income (loss) to net cash provided by / (used in) operating activities:
Depreciation and amortization	2,155	2,058
Share-based compensation	5,944	7,148
Deferred rent obligations	(664)	44
Purchases of securities owned, at fair value	(1,643,802)	(3,709,677)
Proceeds from sales of securities owned, at fair value	1,579,427	3,693,913
Proceeds from sales of securities sold, not yet purchased, at fair value	967,861	1,276,363
Payments to cover securities sold, not yet purchased, at fair value	(994,775)	(1,275,464)
Net (gains) losses on securities, derivatives and other investments	(17,866)	(16,200)
Purchases of securities owned, at fair value, Consolidated Funds	(108,768)	(148,429)
Proceeds from sales of securities owned, at fair value, Consolidated Funds	112,522	149,665
Purchases of other investments, Consolidated Funds	(4,279)	(8,100)
Proceeds from sales of other investments, Consolidated Funds	7,580	58,982
Net realized and unrealized (gains) losses on investments and other transactions, Consolidated Funds	(6,323)	(883)
(Increase) decrease in operating assets:
Cash collateral pledged	47	(19)
Securities owned, at fair value, held at broker dealer	26,836	(11,835)
Receivable from brokers	(4,778)	42,843
Fees receivable	3,317	(1,482)
Due from related parties	(724)	5,841
Other assets	304	(6,312)
Cash and cash equivalents, Consolidated Funds	(1,322)	5,162
Other assets, Consolidated Funds	1,206	(26)
Increase (decrease) in operating liabilities:
Securities sold, not yet purchased, at fair value, held at broker dealer	14,748	(5,644)
Payable to brokers	(48,314)	33,269
Compensation payable	(51,810)	(57,821)
Fees payable	3,134	(666)
Due to related parties	(927)	(1,806)
Accounts payable, accrued expenses and other liabilities	(3,703)	2,695
Due to related parties, Consolidated Funds	25	0
Accounts payable, accrued expenses and other liabilities, Consolidated Funds	(11)	(1,070)
Net cash provided by (used in) operating activities	(156,724)	33,429
Cash flows from investing activities:
Securities purchased under agreement to resell	35,253	25,635
Purchases of other investments	(6,441)	(35,683)
Proceeds from sales of other investments	9,253	35,577
Purchase of fixed assets	(445)	(2,543)
Net cash provided by (used in) investing activities	37,620	22,986
Cash flows from financing activities:
Securities sold under agreement to repurchase	65,408	(36,493)
Repayments on short-term borrowings and other debt	(375)	(1,521)
Purchase of treasury stock	(905)	0
Capital withdrawals to noncontrolling interests in operating entities	(2,042)	0
Capital contributions by non-controlling interest in Consolidated Funds	0	3,504
Capital withdrawals to non-controlling interest in Consolidated Funds	(3,653)	(32,008)
Net cash provided by (used in) financing activities	58,433	(66,518)
Change in cash and cash equivalents	(60,671)	(10,103)
Cash and cash equivalents at beginning of year	126,889	36,354
Cash and cash equivalents at end of year	66,218	26,251
Supplemental non-cash information:
Net assets of consolidated funds	19,073	0
Net assets of deconsolidated funds	$ 17,104	$ 0