Consolidated Statements of Cash Flows - USD ($) $ / shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Cash flows from operating activities:
Net income (loss)	$ 152,066	$ (72,111)
Adjustments to reconcile net income (loss) to net cash provided by / (used in) operating activities:
Bargain Purchase Gain, net of tax	3,855	0
Depreciation and amortization	4,354	5,442
Amortization of debt issuance costs	480	334
Amortization of debt discount (premium)	776	1,109
Noncash lease expense	(362)	(1,200)
Gain (Loss) on Extinguishment of Debt	3,890	0
Share-based compensation	19,037	8,281
Change in deferred taxes	5,913	(1,682)
Contingent Liability adjustment	(614)	0
Purchases of securities owned, at fair value	(269,073)	(749,807)
Proceeds from sales of securities owned, at fair value	271,314	845,779
Proceeds from sales of securities sold, not yet purchased, at fair value	63,511	416,453
Payments to cover securities sold, not yet purchased, at fair value	(58,346)	(334,068)
Proceeds from other investments	16,995	15,693
Investment income (loss) principal transactions, net	(158,833)	38,039
Consolidated Funds
Purchases of securities owned, at fair value	0	(1,024,733)
Proceeds from sales of securities owned, at fair value	2,687	991,096
Purchases of other investments	0	(1,240)
Proceeds from other investments	14,130	6,669
Investment Income (loss) principal transactions, net	3,143	74,071
(Increase) decrease in operating assets:
Securities owned, at fair value, held at broker-dealer	(1,112,154)	713,313
Receivable on derivative contracts, at fair value	(44,054)	(20,889)
Securities borrowed	(88,570)	(216,989)
Deposits with clearing organizations, brokers and banks	22,874	(40,193)
Receivable from brokers, dealers and clearing organizations	(191,009)	(91,622)
Receivable from customers, net of allowance	(95,705)	(87,362)
Fees receivable, net of allowance	(46,170)	(30,723)
Due from related parties	440	1,947
Other assets	(9,344)	(6,919)
Consolidated Funds
Cash and cash equivalents	(6,138)	(8,847)
Receivable on derivative contracts, at fair value	(2,917)	(11,459)
Receivable from brokers	0	5,296
Other assets	13	(94)
Increase (decrease) in operating liabilities:
Securities sold, not yet purchased, at fair value, held at broker dealer	187,749	15,925
Securities sold under agreement to repurchase	(2,490)	34,176
Payable for derivative contracts, at fair value	(24,035)	11,624
Securities loaned	607,531	(604,072)
Payable to brokers, dealers and clearing organizations	73,328	59,078
Payable to customers	977,274	58,590
Commission management payable	22,634	41,068
Compensation payable	(17,809)	(156,333)
Fees payable	(918)	(378)
Due to related parties	48	0
Accounts payable, accrued expenses and other liabilities	41,793	23,974
Consolidated Funds
Contributions received in advance	0	150
Payable to brokers	0	399
Payable for derivative contracts, at fair value	0	13,297
Due To Related Parties, Consolidated Funds	0	(581)
Accounts payable, accrued expenses and other liabilities	(359)	382
Net Cash Provided by (Used in) Operating Activities	359,225	(79,117)
Cash flows from investing activities:
Securities purchased under agreement to resell	191	0
Purchases of other investments	(29,117)	(17,650)
Purchase of business (see note 3)	2,109	0
Proceeds from sales of other investments	31,267	12,059
Purchase of fixed assets and intangibles	(1,643)	(2,485)
Net Cash Provided by (Used in) Investing Activities	2,807	(8,076)
Cash flows from financing activities:
Deferred Debt Issuance Costs	6,467	0
Borrowings on notes and other debt	301,490	62,812
Repayments on notes and other debt	(139,737)	(933)
Purchase of treasury stock	$ (20,629)	$ (18,018)
Cash dividends paid	$ (2,313)	$ (1,168)
Preferred dividends paid	$ (1,698)	$ (1,698)
Contingent liability payment	(10,698)	(782)
Capital contributions by non-controlling interests in operating entities	3,498	286
Capital withdrawals to non-controlling interests in operating entities	(2,348)	(462)
Consolidated Funds
Capital contributions by non-controlling interests in Consolidated Funds	19,017	207,263
Capital withdrawals to non-controlling interests in Consolidated Funds	(16,424)	(166,238)
Net Cash Provided by (Used in) Financing Activities	123,691	81,062
Change in cash and cash equivalents	485,723	(6,131)
Total cash beginning of period	941,053	415,014
Cash and cash equivalents	1,147,531	270,079
Cash collateral pledged	110,303	7,538
Segregated cash	168,942	131,266
Total cash at end of period	1,426,776	408,883
Supplemental information
Cash paid during the year for interest	65,259	29,560
Cash paid during the year for taxes	8,087	950
Purchase of treasury stock, at cost, through net settlement	6,245	2,825
Dividends, Preferred Stock, Cash	(1,698)	(1,698)
Dividends, Cash	2,777	1,429
Net assets (liabilities) acquired upon acquisition (net of cash)	3,107	0
Decrease in noncontrolling interest due to deconsolidation of entity	74,813	0
Common stock issuance upon close of acquisition	$ 2,202	$ 618