Consolidated Statements of Cash Flows - USD ($) $ / shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Cash flows from operating activities:
Net income (loss)	$ (72,111)	$ 10,295
Adjustments to reconcile net income (loss) to net cash provided by / (used in) operating activities:
Depreciation and amortization	5,442	4,956
Amortization of debt issuance costs	334	244
Amortization of debt discount	1,109	1,349
Noncash lease expense	(1,200)	(806)
Share-based compensation	8,281	7,817
Change in deferred taxes	(1,682)	2,253
Purchases of securities owned, at fair value	(749,807)	(299,969)
Proceeds from sales of securities owned, at fair value	845,779	389,551
Proceeds from sales of securities sold, not yet purchased, at fair value	416,453	439,565
Payments to cover securities sold, not yet purchased, at fair value	(334,068)	(361,290)
Proceeds from other investments	15,693	3,529
Net (gains) losses on securities, derivatives and other investments	38,039	(32,320)
Consolidated Funds
Purchases of securities owned, at fair value	(1,024,733)	(674,220)
Proceeds from sales of securities owned, at fair value	991,096	565,460
Purchases of other investments	(1,240)	(296)
Proceeds from other investments	6,669	1,174
Net realized and unrealized (gains) losses on investments and other transactions	74,071	(14,309)
(Increase) decrease in operating assets:
Securities owned, at fair value, held at broker-dealer	713,313	(105,939)
Receivable on derivative contracts, at fair value	(20,889)	3,462
Securities borrowed	(216,989)	(559,062)
Deposits with clearing organizations, brokers and banks	(40,193)	(19,887)
Receivable from brokers, dealers and clearing organizations	(91,622)	123,041
Receivable from customers, net of allowance	(87,362)	1,139
Fees receivable, net of allowance	(30,723)	(10,884)
Due from related parties	1,947	5,028
Other assets	(6,919)	(13,688)
Consolidated Funds
Cash and cash equivalents	(8,847)	35,995
Receivable on derivative contracts, at fair value	(11,459)	1,232
Receivable from brokers	5,296	(31,223)
Other assets	(94)	(22,456)
Increase (decrease) in operating liabilities:
Securities sold, not yet purchased, at fair value, held at broker dealer	15,925	283,919
Securities sold under agreement to repurchase	34,176	0
Payable for derivative contracts, at fair value	11,624	27,501
Securities loaned	(604,072)	437,351
Payable to brokers, dealers and clearing organizations	59,078	(54,199)
Payable to customers	58,590	(112,103)
Commission management payable	41,068	8,364
Compensation payable	(156,333)	(159,154)
Fees payable	(378)	(11,226)
Due to related parties	0	(4,561)
Accounts payable, accrued expenses and other liabilities	24,234	9,272
Consolidated Funds
Contributions received in advance	150	1,000
Payable to brokers	399	(9,618)
Payable for derivative contracts, at fair value	13,297	3,894
Due To Related Parties, Consolidated Funds	(581)	0
Accounts payable, accrued expenses and other liabilities	382	(211)
Net Cash Provided by (Used in) Operating Activities	(78,857)	(130,030)
Cash flows from investing activities:
Purchases of other investments	(17,650)	(5,462)
Purchase of business	0	(48,581)
Proceeds from sales of other investments	12,059	6,337
Proceeds from loans held for investment	0	13
Purchase of fixed assets	(2,485)	(1,684)
Net Cash Provided by (Used in) Investing Activities	(8,076)	(49,377)
Cash flows from financing activities:
Repayments on convertible debt	0	(20,860)
Borrowings on notes and other debt	62,812	1,579
Repayments on notes and other debt	(933)	(394)
Purchase of treasury stock	$ (18,018)	$ (4,658)
Cash dividends paid	$ (1,428)	$ 0
Preferred stock dividends	$ (1,698)	$ (1,698)
Contingent liability payment	(782)	(1,235)
Capital contributions by redeemable non-controlling interests in operating entities	286	2,025
Capital withdrawals to redeemable non-controlling interests in operating entities	(462)	(346)
Consolidated Funds
Capital contributions by redeemable non-controlling interests in Consolidated Funds	207,263	159,948
Capital withdrawals to redeemable non-controlling interests in Consolidated Funds	(166,238)	(17,845)
Net Cash Provided by (Used in) Financing Activities	80,802	116,516
Change in cash and cash equivalents	(6,131)	(62,891)
Total cash beginning of period	415,014	442,113
Cash and cash equivalents	270,079	235,838
Cash collateral pledged	7,538	6,420
Segregated cash	131,266	136,964
Total cash at end of period	408,883	379,222
Supplemental information
Cash paid during the year for interest	29,560	8,822
Cash paid during the year for taxes	950	1,431
Purchase of treasury stock, at cost, through net settlement	2,825	4,671
Net assets (liabilities) acquired upon acquisition (net of cash)		90,727
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		97,655
Common stock issuance upon close of acquisition	$ 618	$ 14,446