Condensed Consolidated Statements of Cash Flows (USD $)	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Cash flows from operating activities:
Net income (loss) from continuing operations	$ 17,840,000	$ (23,957,000)	$ (78,537,000)
Net income (loss) from discontinued operations, net of tax	0	0	(23,646,000)
Adjustments to reconcile net income (loss) to net cash provided by / (used in) operating activities:
Bargain purchase gain	0	0	22,244,000
Depreciation and amortization	10,227,000	9,437,000	26,864,000
Share-based compensation	17,915,000	24,784,000	28,308,000
Deferred rent obligations	(268,000)	(1,938,000)	(4,061,000)
Net loss on disposal of fixed assets	410,000	30,000	103,000
Goodwill impairment	0	0	7,151,000
Purchases of securities owned, at fair value	(6,821,969,000)	(6,257,362,000)	(8,953,879,000)
Proceeds from sales of securities owend, at fair value	7,106,181,000	6,328,288,000	8,726,114,000
Proceeds from sales of securities sold, not yet purchased, at fair value	2,767,452,000	4,327,700,000	4,690,844,000
Payments to cover securities sold, not yet purchased, at fair value	(2,789,081,000)	(4,456,056,000)	(4,553,832,000)
Net (gains) losses on securities, derivatives and other investments	(40,510,000)	(43,872,000)	(3,128,000)
Consolidated Funds
Purchases of securities owned, at fair value	(298,220,000)	(366,388,000)	(480,251,000)
Proceeds from sales of securities owned, at fair value	287,412,000	369,209,000	482,630,000
Proceeds from sales of securities sold, not yet purchased, at fair value	42,701,000	0	0
Payments to cover securities sold, not yet purchased, at fair value	(42,387,000)	0	0
Purchases of other investments	(4,497,000)	(9,785,000)	(18,356,000)
Proceeds from sales of other investments	56,873,000	42,071,000	127,664,000
Net realized and unrealized (gains) losses on investments and other transactions	(14,153,000)	(8,608,000)	(4,746,000)
(Increase) decrease in operating assets:
Cash acquired upon transaction	10,747,000	290,000	117,496,000
Cash collateral pledged	135,000	625,000	(25,000)
Securities owned, at fair value, held at broker dealer	20,434,000	43,657,000	152,080,000
Securities borrowed	(521,447,000)	119,758,000	0
Receivable from brokers	5,614,000	405,000	127,995,000
Fees receivable, net of allowance	(9,975,000)	(5,642,000)	9,041,000
Due from related parties	(5,888,000)	(3,570,000)	2,388,000
Other assets	1,304,000	10,661,000	(1,388,000)
Consolidated Funds
Cash and cash equivalents	1,511,000	(2,326,000)	6,913,000
Other assets	(5,528,000)	1,370,000	469,000
Increase (decrease) in operating liabilities:
Securities sold, not yet purchased, at fair value, held at broker dealer	(11,898,000)	(1,301,000)	(157,134,000)
Securities loaned	509,605,000	(132,927,000)	0
Payable to brokers	(113,368,000)	(24,572,000)	46,169,000
Compensation payable	(13,036,000)	(29,047,000)	(12,107,000)
Fees payable	1,047,000	(985,000)	(3,772,000)
Due to related parties	(280,000)	(1,252,000)	(7,273,000)
Accounts payable, accrued expenses and other liabilities	(15,490,000)	(12,737,000)	6,652,000
Consolidated Funds
Payable to brokers	1,030,000	0	0
Due to related parties	0	25,000	0
Accounts payable, accrued expenses and other liabilities	146,000	149,000	(1,582,000)
Net cash provided by / (used in) operating activities	150,589,000	(103,866,000)	232,920,000
Cash flows from investing activities:
Securities purchased under agreement to resell	0	166,260,000	(68,505,000)
Purchases of other investments	(20,048,000)	(14,848,000)	(61,364,000)
Proceeds from sales of other investments	29,900,000	13,298,000	53,317,000
Purchase of business, net of cash acquired (Note 2)	0	(10,853,000)	0
Cash paid to acquire net assets (contingent payable)	(779,000)	0	0
Purchase of fixed assets	(1,141,000)	(1,902,000)	(6,539,000)
Net cash provided by / (used in) investing activities	7,932,000	151,955,000	(83,091,000)
Cash flows from financing activities:
Securities sold under agreement to repurchase	(162,288,000)	(62,838,000)	36,618,000
Borrowings on short-term borrowings and other debt	2,044,000	0	493,000
Repayments on short-term borrowings and other debt	(3,613,000)	(1,518,000)	(26,576,000)
Purchase of treasury stock	(12,732,000)	(10,838,000)	(11,365,000)
Capital contributions by non-controlling interests in operating entities	501,000	0	0
Capital withdrawals to non-controlling interests in operating entities	(3,058,000)	(3,167,000)	(5,009,000)
Consolidated Funds
Capital contributions by non-controlling interests in Consolidated Funds	14,680,000	0	4,038,000
Capital withdrawals to non-controlling interests in Consolidated Funds	(22,873,000)	(15,065,000)	(55,507,000)
Net cash provided by / (used in) financing activities	(187,339,000)	(93,426,000)	(57,308,000)
Change in cash and cash equivalents	(28,818,000)	(45,337,000)	92,521,000
Cash and cash equivalents at beginning of period	83,538,000	128,875,000	36,354,000
Cash and cash equivalents at end of period	54,720,000	83,538,000	128,875,000
Supplemental information
Cash paid during the year for interest	24,644,000	9,419,000	9,007,000
Cash paid during the year for taxes	72,000	611,000	871,000
Purchase of treasury stock, at cost, upon close of acquisition (see Note 2)	0	0	1,906,000
Net assets (liabilities) acquired upon acquisition (net of cash) (See Note 2)	0	9,995,000	58,486,000
Non compete agreements and covenants with limiting conditions acquired (see Note 2)	460,000	167,000	2,310,000
Common stock issuance upon close of acquisition (see Note 2)	6,240,000	0	156,048,000
Purchase of treasury stock, at cost, through net settlement (see Note 21)	3,649,000	3,988,000	3,631,000
Re-issuance of treasury stock for services provided	65,000
Re-issuance of treasury stock for services provided	90,000		0
Net assets transferred to Merger Master (see Note 6)	22,152,000	0	0
Net assets of consolidated entities	0	18,521,000	3,470,000
Net assets of deconsolidated entities	$ 0	$ 17,104,000	$ 0