Consolidated Statements of Cash Flows - USD ($) $ / shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Cash flows from operating activities:
Net income (loss)	$ 207,064	$ 55,870	$ 79,879
Adjustments to reconcile net income (loss) to net cash provided by / (used in) operating activities:
Depreciation and amortization	22,677	20,460	12,436
Goodwill Impairment	0	4,100	0
Amortization of debt issuance costs	1,512	1,129	1,153
Amortization of debt discount (premium)	4,490	4,598	5,473
Noncash lease expense	(561)	(2,148)	0
Impairment of Leasehold	2,425	0	0
Gain (Loss) on Extinguishment of Debt, Cash Portion	(2,719)	0	652
Share-based compensation	48,222	33,918	37,018
Change in deferred taxes	70,136	13,295	15,486
Deferred rent obligations	0	0	(3,036)
Gain (Loss) on disposal of fixed assets	0	(233)	(15,343)
Purchases of securities owned, at fair value	(1,682,598)	(2,107,956)	(3,830,757)
Proceeds from sales of securities owned, at fair value	1,793,934	2,042,946	4,032,937
Proceeds from sales of securities sold, not yet purchased, at fair value	821,829	1,360,075	2,794,434
Payments to cover securities sold, not yet purchased, at fair value	(850,608)	(1,408,043)	(2,927,916)
Proceeds from other investments	22,453	23,886	10,157
Net (gains) losses on securities, derivatives and other investments	(161,699)	(74,284)	(54,032)
Consolidated Funds
Purchases of securities owned, at fair value	(1,912,137)	(2,725,439)	(887,728)
Proceeds from sales of securities owned, at fair value	1,793,528	2,618,200	835,002
Purchases of other investments	(2,090)	(3,408)	(2,835)
Proceeds from other investments	6,734	23,954	231,559
Net realized and unrealized (gains) losses on investments and other transactions	21,597	(90,900)	(52,807)
(Increase) decrease in operating assets:
Securities owned, at fair value, held at broker-dealer	(335,510)	(990,356)	(57,732)
Receivable on derivative contracts, at fair value	11,394	(37,522)	44,053
Securities borrowed	(1,153,746)	(346,646)	35,353
Deposits with clearing organizations, brokers and banks	(13,197)	(2,332)	4,573
Receivable from brokers, dealers and clearing organizations	(1,048,049)	104,418	(277,935)
Receivable from customers, net of allowance	1,684	(67,789)	12,033
Fees receivable, net of allowance	(33,991)	(7,143)	(6,401)
Due from related parties	5,498	7,120	1,405
Other assets	63,626	(6,501)	6,017
Consolidated Funds
Cash and cash equivalents	8,075	7,299	(19,501)
Receivable on derivative contracts, at fair value	(19,710)	(1,417)	(1,896)
Receivable from brokers	(961)	(17,636)	(2,684)
Other assets	564	(159)	(538)
Increase (decrease) in operating liabilities:
Securities sold, not yet purchased, at fair value, held at broker dealer	286,105	277,119	26,232
Securities sold under agreement to repurchase	(18,208)	23,244	0
Payable for derivative contracts, at fair value	15,399	44,679	2,305
Securities loaned	874,548	1,187,014	(41,979)
Payable to brokers, dealers and clearing organizations	144,125	42,287	(23,422)
Payable to customers	1,250,102	(94,929)	172,686
Commission management payable	45,367	(23,650)	24,819
Compensation payable	134,522	(38,954)	64,456
Fees payable	22,293	(1,025)	14,518
Due to related parties	254	(5,320)	1
Accounts payable, accrued expenses and other liabilities	55,879	(3,148)	17,723
Consolidated Funds
Contributions received in advance	450	50	0
Payable to brokers	8,560	(22,657)	22,770
Payable for derivative contracts, at fair value	11,967	3,106	(5,467)
Due To Related Parties, Consolidated Funds	(386)	581	0
Accounts payable, accrued expenses and other liabilities	436	(129)	369
Net Cash Provided by (Used in) Operating Activities	521,279	(179,910)	324,176
Cash flows from investing activities:
Securities purchased under agreement to resell	(191)	0	0
Purchases of other investments	(48,634)	(19,812)	(28,092)
Purchase of business	(5,647)	(48,581)	0
Proceeds from sales of other investments	44,371	35,648	18,782
Proceeds from loans held for investment	0	0	14
Purchase of fixed assets and intangibles	(10,721)	(14,882)	(8,586)
Net Cash Provided by (Used in) Investing Activities	(20,822)	(47,627)	(17,882)
Cash flows from financing activities:
Repayments on convertible debt	(69,841)	(14,068)	(6,708)
Payments of Debt Issuance Costs	1,700	2,077	3,985
Borrowings on notes and other debt	159,821	87,365	102,382
Repayments on notes and other debt	(121,472)	(10,263)	(16,601)
Purchase of treasury stock	$ (47,314)	$ (15,217)	$ (31,762)
Cash dividends paid	$ (5,710)	$ 0	$ 0
Preferred dividends paid	$ (6,792)	$ (6,792)	$ (6,792)
Contingent liability payment	(5,653)	(1,234)	(797)
Capital contributions by non-controlling interests in operating entities	9,730	11,110	941
Capital withdrawals to non-controlling interests in operating entities	(5,605)	(3,785)	(2,774)
Consolidated Funds
Capital contributions by non-controlling interests in Consolidated Funds	375,715	267,049	114,064
Capital withdrawals to non-controlling interests in Consolidated Funds	(255,597)	(111,650)	(276,357)
Net Cash Provided by (Used in) Financing Activities	25,582	200,438	(128,389)
Change in cash and cash equivalents	526,039	(27,099)	177,905
Total cash beginning of period	415,014	442,113	264,208
Cash and cash equivalents	645,169	301,123	259,148
Cash collateral pledged	110,743	6,563	6,318
Segregated cash	185,141	107,328	176,647
Total cash at end of period	941,053	415,014	442,113
Supplemental information
Cash paid during the year for interest	153,653	145,877	90,843
Cash paid during the year for taxes	4,783	4,310	3,881
Purchase of treasury stock, at cost, through net settlement	15,147	15,217	12,310
Dividends, Preferred Stock, Cash	(6,792)	(6,792)	(6,792)
Net assets (liabilities) acquired upon acquisition (net of cash)	9,865	90,727	0
Initial recognition of right of use asset		103,694
Initial recognition of lease liability		110,505
Noncash transfer of net assets from Unconsolidated Master Fund to Consolidated Fund			8,820
Decrease in noncontrolling interest due to deconsolidation of entity	450,600		32,559
Increase in noncontrolling interest due to consolidation of entity	48,596
Embedded Derivative, No Longer Bifurcated, Amount Reclassified to Stockholders' Equity			28,974
Common stock issuance upon close of acquisition	$ 926	14,446	0
Noncash transfer of net assets from Unconsolidated Master Fund to Consolidated Fund			$ 8,820
Merger Master
Supplemental information
Noncash transfer of net assets from Unconsolidated Master Fund to Consolidated Fund		97,655
Noncash transfer of net assets from Unconsolidated Master Fund to Consolidated Fund		$ 97,655