Condensed Consolidated Statements of Cash Flows (USD $) In Thousands, unless otherwise specified	9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011
Statement of Cash Flows [Abstract]
Net income (loss) from continuing operations	$ (15,761)	$ (20,553)
Cash flows from operating activities:
Net income (loss) from discontinued operations, net of tax	0	(5,087)
Adjustments to reconcile net income (loss) to net cash provided by / (used in) operating activities:
Bargain purchase gain	0	(22,244)
Depreciation and amortization	6,945	7,397
Share-based compensation	20,578	20,236
Deferred rent obligations	(1,316)	(718)
Purchases of securities owned, at fair value	(4,776,378)	(6,750,192)
Proceeds from sales of securities owned, at fair value	4,818,865	6,524,723
Proceeds from sales of securities sold, not yet purchased, at fair value	3,487,601	3,464,059
Payments to cover securities sold, not yet purchased, at fair value	(3,582,578)	(3,246,988)
Net (gains) losses on securities, derivatives and other investments	(33,576)	11,239
Consolidated Funds
Purchases of securities owned, at fair value, Consolidated Funds	(249,731)	(368,933)
Proceeds from sales of securities owned, at fair value, Consolidated Funds	252,966	373,392
Purchases of other investments, Consolidated Funds	(8,273)	(15,108)
Proceeds from sales of other investments, Consolidated Funds	33,795	106,611
Net realized and unrealized (gains) losses on investments and other transactions, Consolidated Funds	(2,718)	(1,729)
(Increase) decrease in operating assets:
Cash acquired upon transaction	0	117,496
Cash collateral pledged	516	(4)
Securities owned, at fair value, held at broker dealer	56,796	95,813
Receivable from brokers	(41,779)	68,075
Fees receivable	934	10,116
Due from related parties	(188)	(2,154)
Other assets	4,158	(16,960)
Consolidated Funds
Cash and cash equivalents, Consolidated Funds	(659)	7,019
Other assets, Consolidated Funds	1,290	475
Increase (decrease) in operating liabilities:
Securities sold, not yet purchased, at fair value, held at broker dealer	(13,086)	(131,773)
Payable to brokers	(10,110)	169,558
Compensation payable	(46,323)	(46,404)
Fees payable	(587)	(6,564)
Due to related parties	(1,268)	(7,705)
Accounts payable, accrued expenses and other liabilities	(4,487)	(611)
Consolidated Funds
Due to related parties, Consolidated Funds	25	0
Accounts payable, accrued expenses and other liabilities, Consolidated Funds	777	(1,611)
Net cash provided by / (used in) operating activities	(103,196)	335,179
Cash flows from investing activities:
Securities purchased under agreement to resell	166,260	(140,394)
Purchases of other investments	(4,291)	(56,565)
Purchase of business, net of cash acquired (See Note 2)	(10,063)	0
Proceeds from sales of other investments	9,036	52,134
Purchase of fixed assets	(1,695)	(5,786)
Net cash provided by / (used in) investing activities	159,247	(150,611)
Cash flows from financing activities:
Securities sold under agreement to repurchase	(104,944)	(53,328)
Borrowings on short-term borrowings and other debt	0	493
Repayments on short-term borrowings and other debt	(1,134)	(26,204)
Purchase of treasury stock	(8,252)	(8,228)
Capital withdrawals to noncontrolling interests in operating entities	(2,717)	(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	(12,103)	(52,164)
Net cash provided by / (used in) financing activities	(129,150)	(137,402)
Change in cash and cash equivalents	(73,099)	47,166
Cash and cash equivalents at beginning of year	128,875	36,354
Cash and cash equivalents at end of year	55,776	83,520
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)	2,652	1,566
Net assets of consolidated entities	18,521	3,470
Net assets of deconsolidated entities	$ 17,104	$ 0