Consolidated Statements of Cash Flows (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Statement of Cash Flows [Abstract]
Interest Paid	$ 9,419	$ 9,007	$ 6,943
Income Taxes Paid	611	871	1,310
Cash flows from operating activities:
Net income (loss) from continuing operations	(23,957)	(78,537)	(31,690)
Net income (loss) from discontinued operations, net of tax	0	(23,646)	0
Adjustments to reconcile net income (loss) to net cash provided by / (used in) operating activities:
Bargain purchase gain	0	(22,244)	0
Depreciation and amortization	9,437	26,864	11,543
Share-based compensation	24,784	28,308	20,608
Deferred rent obligations	(1,938)	(4,061)	(8,574)
Net loss on disposal of fixed assets	30	103	299
Goodwill impairment	0	(7,151)	0
Purchases of securities owned, at fair value	(6,257,362)	(8,953,879)	(3,415,775)
Proceeds from sales of securities owned, at fair value	6,328,288	8,726,114	2,943,376
Proceeds from sales of securities sold, not yet purchased, at fair value	4,327,700	4,690,844	2,678,922
Payments to cover securities sold, not yet purchased, at fair value	(4,456,056)	(4,553,832)	(2,556,056)
Net (gains) losses on securities, derivatives and other investments	(43,872)	(3,128)	(20,339)
Consolidated Funds
Purchases of securities owned, at fair value, Consolidated Funds	(366,388)	(480,251)	(445,913)
Proceeds from sales of securities owned, at fair value, Consolidated Funds	369,209	482,630	437,147
Purchases of other investments, Consolidated Funds	(9,785)	(18,356)	(30,583)
Proceeds from sales of other investments, Consolidated Funds	42,071	127,664	285,915
Net realized and unrealized (gains) losses on investments and other transactions, Consolidated Funds	(8,608)	(4,746)	(34,316)
(Increase) decrease in operating assets:
Cash acquired upon transaction	290	117,496	0
Cash collateral pledged	625	(25)	(8,132)
Securities owned, at fair value, held at broker dealer	43,657	152,080	50,895
Securities Borrowed	119,758	0	0
Receivable from brokers	405	127,995	(63,619)
Fees receivable	(5,642)	9,041	(9,035)
Due from related parties	(3,570)	2,388	(1,510)
Other assets	10,661	(1,388)	5,040
Consolidated Funds
Cash and cash equivalents, Consolidated Funds	(2,326)	6,913	(4,024)
Other assets, Consolidated Funds	1,370	469	215
Increase (decrease) in operating liabilities:
Securities sold, not yet purchased, at fair value, held at broker dealer	(1,301)	(157,134)	75,075
Securities Loaned	(132,927)	0	0
Payable to brokers	(24,572)	46,169	81,838
Compensation payable	(29,047)	(12,107)	(4,248)
Fees payable	(985)	(3,772)	3,076
Due to related parties	(1,252)	(7,273)	1,084
Accounts payable, accrued expenses and other liabilities	(12,737)	6,652	(14,424)
Consolidated Funds
Due to related parties, Consolidated Funds	25	0	0
Accounts payable, accrued expenses and other liabilities, Consolidated Funds	149	(1,582)	1,652
Net cash provided by / (used in) operating activities	(103,866)	232,920	(51,553)
Cash flows from investing activities:
Securities purchased under agreement to resell	166,260	(68,505)	(97,755)
Purchases of other investments	(14,848)	(61,364)	(321,914)
Purchase of business, net of cash acquired (See Note 2)	(10,853)	0	0
Proceeds from sales of other investments	13,298	53,317	316,063
Purchase of fixed assets	(1,902)	(6,539)	(5,853)
Net cash provided by / (used in) investing activities	151,955	(83,091)	(109,459)
Cash flows from financing activities:
Securities sold under agreement to repurchase	(62,838)	36,618	192,165
Borrowings on short-term borrowings and other debt	0	493	8,059
Repayments on short-term borrowings and other debt	(1,518)	(26,576)	(25,663)
Purchase of treasury stock	(10,838)	(11,365)	0
Capital withdrawals to noncontrolling interests in operating entities	(3,167)	(5,009)	0
Consolidated Funds
Capital contributions by non-controlling interests in Consolidated Funds	0	4,038	10,062
Capital withdrawals to non-controlling interests in Consolidated Funds	(15,065)	(55,507)	(134,624)
Net cash provided by / (used in) financing activities	(93,426)	(57,308)	49,999
Change in cash and cash equivalents	(45,337)	92,521	(111,013)
Cash and cash equivalents at beginning of year	128,875	36,354	147,367
Cash and cash equivalents at end of year	83,538	128,875	36,354
Supplemental non-cash information
Purchase of treasury stock, at cost, upon close of acquisition (see Note 2)	0	1,906	0
Net assets acquired upon acquisition (net of cash) (See Note 2)	9,995	58,486	0
Non compete agreements and covenants with limiting conditions acquired (see Note 2)	167	2,310	0
Common stock issuance upon close of acquisition (see Note 2)	0	156,048	0
Purchase of treasury stock, at cost, through net settlement (See Note 15)	3,988	3,631	0
Net assets of consolidated entities	18,521	3,470	0
Net assets of deconsolidated entities	17,104	0	6,816
Net settlement of cash collateral pledged with repayments on the line of credit	0	0	6,746
Fair Value of Assets Acquired	$ 0	$ 0	$ 6,337