Consolidated Statements of Cash Flows - USD ($)	3 Months Ended			6 Months Ended		12 Months Ended
	Jun. 30, 2019		Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018
Cash flows from operating activities:
Net income (loss)	$ 10,143,000		$ 30,006,000	$ 22,132,000	$ 58,015,000
Adjustments to reconcile net income (loss) to net cash provided by / (used in) operating activities:
Depreciation and amortization	4,952,000		3,194,000	9,908,000	6,419,000
Amortization of debt issuance costs				509,000	656,000
Amortization of debt discount				2,419,000	2,871,000
Noncash lease expense				(1,632,000)	0
Gain / (loss) on extinguishment of debt				0	(652,000)
Share-based compensation				17,181,000	19,080,000
Change in deferred taxes				5,997,000	10,953,000
Deferred rent obligations				0	(939,000)
Gain (Loss) on Disposition of Property Plant Equipment				(97,000)	(155,000)
Goodwill, Impairment Loss	4,100,000	[1],[2],[3],[4]	0	4,100,000	0	$ 0
Purchases of securities owned, at fair value				(900,815,000)	(2,525,789,000)
Proceeds from sales of securities owned, at fair value				751,611,000	2,779,569,000
Proceeds from sales of securities sold, not yet purchased, at fair value				639,630,000	1,789,059,000
Payments to cover securities sold, not yet purchased, at fair value				(590,363,000)	(1,940,907,000)
Proceeds from the sale of other investments				8,174,000	3,870,000
Net (gains) losses on securities, derivatives and other investments				(42,314,000)	(28,237,000)
Consolidated Funds
Purchases of securities owned, at fair value				(1,421,720,000)	(306,995,000)
Proceeds from sales of securities owned, at fair value				1,280,181,000	344,079,000
Purchases of other investments				(2,798,000)	(1,414,000)
Proceeds from sales of other investments				17,168,000	10,289,000
Net realized and unrealized (gains) losses on investments and other transactions				(22,496,000)	(47,628,000)
(Increase) decrease in operating assets:
Securities owned, at fair value, held at broker-dealer				(201,355,000)	(89,077,000)
Receivable on derivative contracts, at fair value				(7,095,000)	43,982,000
Securities borrowed				(982,571,000)	(104,973,000)
Deposits with clearing organizations, brokers and banks				(8,300,000)	(660,000)
Receivable from brokers, dealers and clearing organizations				168,745,000	(159,702,000)
Increase (decrease) from receivable from customers				(49,622,000)	(5,321,000)
Fees receivable, net of allowance				(7,285,000)	(32,917,000)
Due from related parties				4,862,000	2,448,000
Other assets				(27,269,000)	13,027,000
Consolidated Funds
Cash and cash equivalents				34,816,000	5,590,000
Receivable on derivative contracts, at fair value				(38,000)	882,000
Receivable from brokers				(11,196,000)	(3,294,000)
Other assets				(963,000)	(91,000)
Increase (decrease) in operating liabilities:
Securities sold, not yet purchased, at fair value, held at broker dealer				177,006,000	30,292,000
Payable for derivative contracts, at fair value				6,363,000	10,097,000
Securities loaned				1,078,134,000	(22,365,000)
Payable to brokers, dealers and clearing organizations				12,281,000	(11,510,000)
Payable to customers				(97,007,000)	168,099,000
Commission management payable				1,461,000	21,721,000
Compensation payable				(119,012,000)	(28,644,000)
Fees payable				23,316,000	15,562,000
Due to related parties				(4,646,000)	4,000
Accounts payable, accrued expenses and other liabilities				18,221,000	6,747,000
Consolidated Funds
Payable to brokers				(12,395,000)	1,241,000
Payable for derivative contracts, at fair value				953,000	(6,085,000)
Accounts payable, accrued expenses and other liabilities				(144,000)	225,000
Net Cash Provided by (Used in) Operating Activities				(225,771,000)	29,036,000
Cash flows from investing activities:
Purchases of other investments				(9,513,000)	(20,227,000)
Purchase of business				(48,581,000)	0
Proceeds from sales of other investments				12,867,000	13,295,000
Proceeds from loans held for investment				0	13,000
Purchase of fixed assets				(3,666,000)	(1,397,000)
Net Cash Provided by (Used in) Investing Activities				(48,893,000)	(8,316,000)
Cash flows from financing activities:
Repayments on convertible debt				(20,860,000)	(13,500,000)
Deferred debt issuance cost				(1,480,000)	(3,883,000)
Borrowings on notes and other debt				55,175,000	105,516,000
Repayments on notes and other debt				(5,051,000)	(2,987,000)
Purchase of treasury stock				(8,079,000)	(10,862,000)
Contingent liability payment				(1,235,000)	(570,000)
Capital contributions by redeemable non-controlling interests in operating entities				11,110,000	200,000
Capital withdrawals to redeemable non-controlling interests in operating entities				(1,346,000)	(1,113,000)
Consolidated Funds
Capital contributions by redeemable non-controlling interests in Consolidated Funds				191,485,000	18,937,000
Capital withdrawals to redeemable non-controlling interests in Consolidated Funds				(58,601,000)	(58,136,000)
Net Cash Provided by (Used in) Financing Activities				161,118,000	33,602,000
Change in cash and cash equivalents				(113,546,000)	54,322,000
Total cash beginning of period				442,113,000	264,208,000	264,208,000
Cash and cash equivalents	182,400,000		207,708,000	182,400,000	207,708,000	259,148,000
Cash collateral pledged	7,097,000		15,513,000	7,097,000	15,513,000	6,318,000
Segregated cash	139,070,000		95,309,000	139,070,000	95,309,000	176,647,000
Total cash at end of period	328,567,000		318,530,000	328,567,000	318,530,000	442,113,000
Supplemental information
Cash paid during the year for interest				52,260,000	39,061,000
Cash paid during the year for taxes				3,580,000	2,233,000
Purchase of treasury stock, at cost, through net settlement				12,015,000	8,376,000
Preferred stock dividends	1,698,000		1,698,000	3,396,000	3,396,000
Net assets (liabilities) acquired upon acquisition (net of cash)				90,727,000	0
Operating right of use assets	101,628,000			101,628,000		0
Operating Lease, Liability	$ 106,873,000			106,873,000		$ 0
Transfer of investment from consolidated funds, securities owned, fair value to securities owned, fair value				97,655,000	8,820,000
Net decrease in redeemable non-controlling interests in Consolidated Funds due to deconsolidation of consolidated fund					32,559,000
Separately recognized conversion option reclassification from a derivative liability to equity			$ 28,973,000		28,973,000
Common stock issuance upon close of acquisition				$ 14,446,000	$ 0

[1] Economic Income (Loss) excludes income taxes and acquisition related adjustments as management does not consider these items when evaluating the performance of the segment.

[2] Economic Income (Loss) presents underwriting expenses net of investment banking revenues, expenses reimbursedfrom clients within their respective expense category. Economic Income (Loss) also records retainer fees, relating to investment banking activities, collectible during the period that would otherwise be deferred until closing for US GAAP reporting

[3] Economic Income (Loss) recognizes Company income from proprietary trading (including interest and dividends

[4] Economic Income (Loss) recognizes the Company's proportionate share of expenses, for certain real estate operating entities and the activist business, for which the investments are recorded under the equity method of accounting for investments.