Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Cash flows from operating activities:
Net income (loss)	$ (37,091)	$ (12,395)	$ 58,975
Adjustments to reconcile net income (loss) to net cash provided by / (used in) operating activities:
Bargain purchase gain, net of tax	(6,914)	0	0
Depreciation and amortization	13,078	12,713	9,498
Net gain on sale of divested business	0	(15,638)	0
Amortization of Debt Issue Costs	1,261	1,208	1,163
Amortization of debt discount	7,435	6,885	6,302
Gain / (loss) on extinguishment of debt	10,551	0	0
Tax benefits (expense) from share based payment arrangements	0	(822)	3,806
Share-based compensation	28,443	26,039	21,740
Deferred tax benefit	45,856	(21,274)	(17,966)
Deferred rent obligations	(2,192)	(880)	(2,333)
Net loss (gain) on disposal of fixed assets	(2,346)	0	54
Contingent liability adjustment	0	2,139	(200)
Purchases of securities owned, at fair value	(4,943,394)	(4,483,975)	(5,856,112)
Proceeds from sales of securities owned, at fair value	5,131,938	4,447,094	6,039,719
Proceeds from sales of securities sold, not yet purchased, at fair value	2,455,876	3,016,934	2,730,939
Payments to cover securities sold, not yet purchased, at fair value	(2,444,010)	(3,054,869)	(2,674,153)
Net (gains) losses on securities, derivatives and other investments	(78,303)	(28,878)	(34,495)
Consolidated Funds
Purchases of securities owned, at fair value	(385,544)	(113,653)	(25,000)
Proceeds from sales of securities owned, at fair value	338,268	73,011	0
Proceeds from sales of securities sold, not yet purchased, at fair value	217	2,226	0
Payments to cover securities sold, not yet purchased, at fair value	(899)	(1,799)	0
Purchases of other investments	(26,206)	(221,897)	(92,305)
Proceeds from sales of other investments	64,867	17,116	31,417
Net realized and unrealized (gains) losses on investments and other transactions	(28,267)	(17,402)	(13,552)
(Increase) decrease in operating assets:
Cash acquired through acquisition	30,562	0	0
Cash collateral pledged	(4,546)	(3,257)	(1,779)
Segregated Cash	13,781	229	(1,253)
Securities owned, at fair value, held at broker dealer	(102,137)	(17,005)	14,877
Receivable on derivative contracts, at fair value	(46,277)	16,717	10,259
Securities Borrowed	(184,827)	0	676,100
Deposits with clearing organizations, brokers and banks	(32,460)	(1,874)	(6,965)
Receivable from brokers, dealers and clearing organizations	(366,297)	31,795	(20,785)
Receivable from customers, net of allowance	(6,422)	0	0
Fees receivable, net of allowance	(29,669)	(12,632)	11,099
Due from related parties	4,815	(176)	(13,344)
Other assets	(33,454)	(10,048)	4,580
Consolidated Funds
Cash and cash equivalents	(4,227)	(3,827)	(13,433)
Receivable on derivative contracts, at fair value	(1,627)	(893)	0
Receivable from brokers	334	(5,978)	0
Other assets	123	152	770
Increase (decrease) in operating liabilities:
Securities sold, not yet purchased, at fair value, held at broker dealer	19,226	7,160	(11,747)
Payable for derivative contracts, at fair value	(1,399)	(421)	(20,147)
Securities Loaned	170,472	0	(682,493)
Payable to brokers, dealers and clearing organizations	(32,440)	78,520	(204,186)
Payables to customers	340,666	0	0
Commission management payable	(15,857)	242	2,225
Compensation payable	9,150	(60,279)	5,540
Fees payable	(639)	(2,366)	(693)
Due to related parties	(3)	244	(145)
Accounts payable, accrued expenses and other liabilities	13,046	(9,133)	(5,337)
Consolidated Funds
Contributions received in advance	(2,000)	1,150	850
Payable to brokers	(2,949)	3,699	0
Payable for derivative contracts, at fair value	6,558	572	0
Due to related parties	(189)	453	3
Accounts payable, accrued expenses and other liabilities	(330)	528	(98)
Net cash provided by / (used in) operating activities	(116,392)	(354,545)	(68,605)
Cash flows from investing activities:
Purchases of other investments	(10,419)	(33,786)	(14,149)
Purchase of business	(55,049)	(6,258)	(38,416)
Proceeds from sales of other investments	71,749	54,068	58,166
Loans issued	(13,745)	0	(46,000)
Proceeds from loans held for investments	3,203	42,800	0
Proceeds from divested business, net of cash divested	0	17,303	0
Purchase of fixed assets	(5,986)	(15,613)	(7,030)
Sale of fixed assets	7,850	0	0
Net cash provided by / (used in) investing activities	(2,397)	58,514	(47,429)
Cash flows from financing activities:
Proceeds from Convertible Debt	135,000	0	0
Repayments on convertible debt	(115,140)	0	0
Proceeds from Issuance of Preferred Stock, net of issuance costs	0	0	117,194
Capped call option transaction	0	0	(15,878)
Deferred Debt Issuance Costs	(7,176)	0	0
Borrowings on notes and other debt	171,148	30,638	7,140
Repayments on notes and other debt	(72,757)	(29,800)	(3,299)
Income tax effect from share-based payment arrangements	0	(822)	3,806
Proceeds from Stock Options Exercised	0	0	394
Purchase of treasury stock	(19,662)	(7,654)	(48,678)
Cash paid to acquire net assets (contingent liability payment)	(393)	(2,358)	(1,725)
Capital contributions to redeemable non-controlling interests in operating entities	0	10	5,644
Capital withdrawals to redeemable non-controlling interests in operating entities	(5,178)	(6,995)	(13,860)
Consolidated Funds
Capital contributions by redeemable non-controlling interests in Consolidated Funds	117,812	276,914	104,533
Capital withdrawals to redeemable non-controlling interests in Consolidated Funds	(65,803)	(10,144)	(11,514)
Net cash provided by / (used in) financing activities	137,851	249,789	143,757
Change in cash and cash equivalents	19,062	(46,242)	27,723
Cash and cash equivalents at beginning of period	110,990	157,232	129,509
Cash and cash equivalents at end of period	130,052	110,990	157,232
Interest Paid	26,632	17,540	17,525
Income Taxes Paid	2,172	5,085	4,161
Supplemental information
Conversion option value on 2022 Convertible Notes	23,387	0	0
Purchase of treasury stock, at cost, through net settlement (See Note 24)	11,889	8,835	8,907
Preferred stock dividends declared (See Note 24)	6,792	6,792	4,075
Net assets (liabilities) acquired upon acquisition (net of cash) (See Note 2)	77,790	0	22,468
Common stock issuance upon close of acquisition (see Note 2)	47,607	0	3,008
Notes payable increase through asset acquisition	0	7,164	0
Net assets of deconsolidated entities	0	73,042	0
Conversion of redeemable non-controlling interest to loan receivable	$ 1,299	$ 0	$ 0