Condensed Consolidated Statements of Cash Flows - USD ($)	9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016
Cash flows from operating activities:
Net income (loss)	$ 50,502,000	$ (19,897,000)
Adjustments to reconcile net income (loss) to net cash provided by / (used in) operating activities:
Bargain purchase gain, net of tax	7,946,000	0
Depreciation and amortization	9,612,000	9,654,000
Net gain on sale of divested business	0	15,638,000
Amortization of Debt Issue Costs	936,000	894,000
Amortization of debt discount	5,601,000	5,107,000
Tax benefits (expense) from share based payment arrangements	0	(764,000)
Share-based compensation	24,702,000	19,271,000
Deferred tax benefit	7,039,000	(6,913,000)
Deferred rent obligations	(1,503,000)	(634,000)
Net loss on disposal of fixed assets	(2,362,000)	0
Contingent liability adjustment	0	2,139,000
Purchases of securities owned, at fair value	(3,442,431,000)	(3,050,670,000)
Proceeds from sales of securities owned, at fair value	3,620,347,000	3,173,147,000
Proceeds from sales of securities sold, not yet purchased, at fair value	1,809,863,000	2,343,063,000
Payments to cover securities sold, not yet purchased, at fair value	(1,799,136,000)	(2,442,968,000)
Net (gains) losses on securities, derivatives and other investments	(76,325,000)	(23,706,000)
Consolidated Funds
Purchases of securities owned, at fair value	(261,863,000)	(60,187,000)
Proceeds from sales of securities owned, at fair value	241,307,000	27,010,000
Proceeds from sales of securities sold, not yet purchased, at fair value	217,000	2,226,000
Payments to cover securities sold, not yet purchased, at fair value	(899,000)	(1,098,000)
Purchases of other investments	(26,206,000)	(221,897,000)
Proceeds from sales of other investments	51,709,000	14,086,000
Net realized and unrealized (gains) losses on investments and other transactions	(43,423,000)	(4,505,000)
(Increase) decrease in operating assets:
Cash Acquired from Acquisition	31,780,000	0
Cash collateral pledged	(3,653,000)	(3,698,000)
Segregated Cash	(11,825,000)	145,000
Securities owned, at fair value, held at broker dealer	(58,126,000)	(26,048,000)
Receivable on derivative contracts, at fair value	(9,204,000)	12,191,000
Securities Borrowed	113,046,000	0
Deposits with clearing organizations, brokers and banks	(22,625,000)	(1,941,000)
Receivable from brokers, dealers and clearing organizations	(105,255,000)	42,067,000
Receivable from customers, net of allowance	(2,040,000)	0
Fees receivable, net of allowance	(28,839,000)	(12,536,000)
Due from related parties	2,222,000	6,914,000
Other assets	(31,415,000)	(23,446,000)
Consolidated Funds
Cash and cash equivalents	6,605,000	3,564,000
Receivable on derivative contracts, at fair value	(149,000)	(429,000)
Receivable from brokers	(2,356,000)	(5,333,000)
Other assets	222,000	(336,000)
Increase (decrease) in operating liabilities:
Securities sold, not yet purchased, at fair value, held at broker dealer	(100,000)	21,954,000
Payable for derivative contracts, at fair value	5,555,000	(4,162,000)
Securities Loaned	128,598,000	0
Payable to brokers, dealers and clearing organizations	(128,490,000)	(4,573,000)
Payables to customers	190,926,000	0
Commission management payable	(8,457,000)	385,000
Compensation payable	(38,092,000)	(99,217,000)
Fees payable	2,807,000	999,000
Due to related parties	(6,000)	(72,000)
Accounts payable, accrued expenses and other liabilities	19,109,000	3,478,000
Consolidated Funds
Contributions received in advance	(2,000,000)	(850,000)
Payable to brokers	(2,289,000)	3,131,000
Payable for derivative contracts, at fair value	1,175,000	276,000
Due to related parties	(189,000)	264,000
Accounts payable, accrued expenses and other liabilities	(438,000)	286,000
Net cash provided by / (used in) operating activities	(19,854,000)	(339,267,000)
Cash flows from investing activities:
Purchases of other investments	(72,834,000)	(25,689,000)
Purchase of business	(54,017,000)	(6,258,000)
Proceeds from sales of other investments	118,130,000	29,814,000
Proceeds from loans held for investments	3,200,000	41,600,000
Proceeds from Divested Businesses, Net of Cash Divested	0	17,303,000
Purchase of fixed assets	(3,056,000)	(14,913,000)
Proceeds from Sale of Property, Plant, and Equipment	7,850,000
Net cash provided by / (used in) investing activities	(727,000)	41,857,000
Cash flows from financing activities:
Borrowings on notes and other debt	31,737,000	30,638,000
Repayments on notes and other debt	(8,845,000)	(28,345,000)
Income tax effect from share-based payment arrangements	0	(764,000)
Purchase of treasury stock	0	(6,014,000)
Cash paid to acquire net assets (contingent liability payment)	(393,000)	(2,358,000)
Capital withdrawals to redeemable non-controlling interests in operating entities	(4,628,000)	(6,995,000)
Consolidated Funds
Capital contributions by redeemable non-controlling interests in Consolidated Funds	60,322,000	236,720,000
Capital withdrawals to redeemable non-controlling interests in Consolidated Funds	(50,778,000)	(6,887,000)
Net cash provided by / (used in) financing activities	27,415,000	215,995,000
Change in cash and cash equivalents	6,834,000	(81,415,000)
Cash and cash equivalents at beginning of period	110,990,000	157,232,000
Cash and cash equivalents at end of period	117,824,000	75,817,000
Supplemental information
Purchase of treasury stock, at cost, through net settlement (See Note 18)	11,433,000	8,793,000
Preferred stock dividends declared (See Note 18)	5,094,000	5,094,000
Net assets (liabilities) acquired upon acquisition (net of cash) (See Note 2)	10,220,000	0
Common stock issuance upon close of acquisition (see Note 2)	47,607,000	0
Notes payable increase through asset acquisition	0	7,164,000
Net assets of deconsolidated entities	0	$ 73,042,000
Noncontrolling Interest, Decrease from Redemptions or Purchase of Interests	$ 1,299,000