Segment Reporting (Details)		3 Months Ended				9 Months Ended
		Sep. 30, 2020 USD ($)		Sep. 30, 2019 USD ($)		Sep. 30, 2020 USD ($) segment		Sep. 30, 2019 USD ($)
Segment Reporting Information [Line Items]
Number of reportable segments | segment						2
Revenues
Investment banking		$ 194,341,000		$ 77,292,000		$ 503,351,000		$ 272,103,000
Brokerage		138,483,000		93,995,000		425,069,000		302,840,000
Management fees		11,954,000		7,300,000		35,211,000		21,480,000
Incentive income		127,000		701,000		127,000		724,000
Investment Income		0		0		0		0
Interest and dividends		37,552,000		60,707,000		127,547,000		129,846,000
Reimbursement from affiliates		269,000		238,000		777,000		780,000
Reinsurance premiums		2,505,000		8,146,000		18,943,000		29,068,000
Other revenues		1,369,000		1,237,000		4,709,000		3,228,000
Total revenues		387,735,000		252,047,000		1,120,384,000		768,308,000
Interest expense		37,754,000		56,477,000		125,850,000		125,089,000
Total net revenues		349,981,000		195,570,000		994,534,000		643,219,000
Expenses
Employee compensation and benefits		153,427,000		120,320,000		583,137,000		388,611,000
Other non-compensation expense		89,636,000		92,046,000		286,666,000		276,054,000
Depreciation and amortization		5,682,000		5,082,000		17,324,000		14,990,000
Goodwill Impairment		0		0		0		4,100,000
Total expenses		249,239,000		219,964,000		891,920,000		689,984,000
Other income (loss)
Total other income (loss)		(62,396,000)		32,342,000		54,328,000		82,976,000
Preferred stock dividends		1,698,000		1,698,000		5,094,000		5,094,000
Income (Loss) before income taxes / Economic income (loss)		38,346,000		7,948,000		156,942,000		36,211,000
Consolidated Funds
Revenues
Total revenues		1,135,000		2,431,000		4,650,000		8,239,000
Expenses
Total expenses		494,000		2,516,000		4,793,000		6,229,000
Operating Company
Revenues
Management fees		11,721,000		7,052,000		34,492,000		20,492,000
Incentive income		127,000		701,000		127,000		710,000
Asset Company
Revenues
Management fees		233,000		248,000		719,000		988,000
Incentive income		0		0		0		14,000
Operating Segments | Operating Company
Revenues
Investment banking		185,151,000		69,433,000		474,778,000		254,374,000
Brokerage		167,084,000		110,178,000		466,823,000		346,095,000
Management fees		14,374,000		10,321,000		41,724,000		30,016,000
Incentive income		(2,621,000)		15,251,000		40,829,000		33,998,000
Investment Income		(90,364,000)		10,913,000		32,566,000		13,827,000
Interest and dividends		0		0		0		0
Reimbursement from affiliates		0		0		0		0
Reinsurance premiums		0		0		0		0
Other revenues		(796,000)		(132,000)		(298,000)		5,295,000
Total revenues		272,828,000		215,964,000		1,056,422,000		683,605,000
Interest expense		6,026,000		5,758,000		18,471,000		16,371,000
Total net revenues		266,802,000		210,206,000		1,037,951,000		667,234,000
Expenses
Employee compensation and benefits		152,829,000		121,890,000		582,480,000		386,593,000
Fixed expenses		34,257,000		36,458,000		106,350,000		107,889,000
Variable expenses		37,736,000		37,216,000		121,846,000		113,728,000
Other non-compensation expense		0		0		0		0
Depreciation and amortization		5,670,000		5,073,000		16,756,000		14,957,000
Economic Non-Controlling Interest		2,105,000		661,000		5,584,000		2,944,000
Goodwill Impairment								0
Total expenses		232,597,000		201,298,000		833,016,000		626,111,000
Other income (loss)
Total other income (loss)		0		0		0		0
Preferred stock dividends		1,415,000		1,341,000		4,160,000		4,058,000
Income (Loss) before income taxes / Economic income (loss)		32,790,000		7,567,000		200,775,000		37,065,000
Operating Segments | Operating Company | Consolidated Funds
Revenues
Total revenues		0		0		0		0
Expenses
Total expenses		0		0		0		0
Operating Segments | Asset Company
Revenues
Investment banking		0		0		0		0
Brokerage		0		0		0		0
Management fees		262,000		586,000		634,000		1,788,000
Incentive income		1,319,000		(862,000)		158,000		762,000
Investment Income		(124,000)		822,000		(13,671,000)		5,289,000
Interest and dividends		0		0		0		0
Reimbursement from affiliates		0		0		0		0
Reinsurance premiums		0		0		0		0
Other revenues		2,000		6,000		4,000		56,000
Total revenues		1,459,000		552,000		(12,875,000)		7,895,000
Interest expense		1,109,000		1,389,000		4,014,000		4,046,000
Total net revenues		350,000		(837,000)		(16,889,000)		3,849,000
Expenses
Employee compensation and benefits		957,000		729,000		2,093,000		4,383,000
Fixed expenses		127,000		625,000		378,000		2,485,000
Variable expenses		6,000		40,000		18,000		127,000
Other non-compensation expense		0		0		0		0
Depreciation and amortization		5,000		9,000		17,000		30,000
Economic Non-Controlling Interest		0		0		0		0
Goodwill Impairment								0
Total expenses		1,095,000		1,403,000		2,506,000		7,025,000
Other income (loss)
Total other income (loss)		0		0		0		0
Preferred stock dividends		283,000		357,000		934,000		1,036,000
Income (Loss) before income taxes / Economic income (loss)		(1,028,000)		(2,597,000)		(20,329,000)		(4,212,000)
Operating Segments | Asset Company | Consolidated Funds
Revenues
Total revenues		0		0		0		0
Expenses
Total expenses		0		0		0		0
Adjustments | Management Reclassifications
Revenues
Investment banking	[1],[2]	(9,190,000)		(7,859,000)		(28,573,000)		(17,729,000)
Brokerage	[3],[4]	28,601,000		16,183,000		41,754,000		43,255,000
Management fees	[5],[6]	2,519,000		3,033,000		5,672,000		8,684,000
Incentive income	[6]	(1,462,000)		13,675,000		40,827,000		33,479,000
Investment Income	[7]	(90,488,000)		11,735,000		18,895,000		19,116,000
Interest and dividends	[3]	(37,552,000)		(60,707,000)		(127,547,000)		(129,846,000)
Reimbursement from affiliates	[1]	(269,000)		(265,000)		(827,000)		(874,000)
Reinsurance premiums	[8]	(2,505,000)		(8,146,000)		(18,943,000)		(29,068,000)
Other revenues	[8]	(2,160,000)		(1,389,000)		(4,982,000)		2,109,000
Total revenues		(112,506,000)		(33,740,000)		(73,724,000)		(70,874,000)
Interest expense	[3]	(29,467,000)		(48,238,000)		(99,971,000)		(101,464,000)
Total net revenues		(83,039,000)		14,498,000		26,247,000		30,590,000
Expenses
Employee compensation and benefits	[9]	359,000		2,299,000		1,436,000		2,365,000
Fixed expenses	[6],[10]	37,708,000		37,559,000		111,880,000		112,038,000
Variable expenses	[10]	37,742,000		37,256,000		121,864,000		113,855,000
Other non-compensation expense	[1],[2],[5],[8],[9]	(89,636,000)		(92,046,000)		(286,666,000)		(276,054,000)
Depreciation and amortization		0		0		0		(3,000)
Economic Non-Controlling Interest	[10]	2,105,000		661,000		5,584,000		2,944,000
Goodwill Impairment								0
Total expenses		(11,722,000)		(14,271,000)		(45,902,000)		(44,855,000)
Other income (loss)
Total other income (loss)	[4],[6],[7]	64,896,000		(26,721,000)		(82,006,000)		(73,907,000)
Preferred stock dividends		0		0		0		0
Income (Loss) before income taxes / Economic income (loss)		(6,421,000)		2,048,000		(9,857,000)		1,538,000
Adjustments | Management Reclassifications | Consolidated Funds
Revenues
Total revenues		0		0		0		0
Expenses
Total expenses		0		0		0		0
Adjustments | Income statement adjustments
Revenues
Investment banking		0		0		0		0
Brokerage		0		0		0		0
Management fees		0		0		0		0
Incentive income		0		0		0		0
Investment Income		0		0		0		0
Interest and dividends		0		0		0		0
Reimbursement from affiliates		0		0		0		0
Reinsurance premiums		0		0		0		0
Other revenues		0		0		0		0
Total revenues		0		0		0		0
Interest expense	[11]	(1,152,000)		(1,092,000)		(3,394,000)		(3,208,000)
Total net revenues		1,152,000		1,092,000		3,394,000		3,208,000
Expenses
Employee compensation and benefits		0		0		0		0
Fixed expenses	[12]	(3,324,000)		(476,000)		(5,152,000)		(1,664,000)
Variable expenses		0		0		0		0
Other non-compensation expense		0		0		0		0
Depreciation and amortization		(7,000)	[13]	0		(551,000)	[13]	0
Economic Non-Controlling Interest		0		0		0		0
Goodwill Impairment	[13]							(4,100,000)
Total expenses		(3,331,000)		(476,000)		(5,703,000)		(5,764,000)
Other income (loss)
Total other income (loss)		0		0		0		0
Preferred stock dividends		1,698,000		1,698,000		5,094,000		5,094,000
Income (Loss) before income taxes / Economic income (loss)		2,785,000		(130,000)		4,003,000		3,878,000
Adjustments | Income statement adjustments | Consolidated Funds
Revenues
Total revenues		0		0		0		0
Expenses
Total expenses		0		0		0		0
Adjustments | Funds Consolidation
Revenues
Investment banking	[14]	0		0		0		0
Brokerage	[14]	0		0		0		0
Management fees	[14]	163,000		574,000		1,475,000		1,640,000
Incentive income	[14]	33,000		13,000		33,000		557,000
Investment Income	[14]	0		0		0		0
Interest and dividends	[14]	0		0		0		0
Reimbursement from affiliates	[14]	0		27,000		50,000		94,000
Reinsurance premiums	[14]	0		0		0		0
Other revenues	[14]	(3,000)		26,000		(21,000)		14,000
Total revenues	[14]	(942,000)		(1,791,000)		(3,113,000)		(5,934,000)
Interest expense	[14]	0		0		0		0
Total net revenues	[14]	(942,000)		(1,791,000)		(3,113,000)		(5,934,000)
Expenses
Employee compensation and benefits	[14]	0		0		0		0
Fixed expenses		0	[14]	0	[14]	0	[14]	0
Variable expenses	[14]	0		0		0		0
Other non-compensation expense	[14]	0		0		0		0
Depreciation and amortization	[14]	0		0		0		0
Economic Non-Controlling Interest	[14]	0		0		0		0
Goodwill Impairment	[14]							0
Total expenses	[14]	(494,000)		(2,516,000)		(4,793,000)		(6,229,000)
Other income (loss)
Total other income (loss)	[14]	(2,500,000)		(5,621,000)		27,678,000		(9,069,000)
Preferred stock dividends	[14]	0		0		0		0
Income (Loss) before income taxes / Economic income (loss)		(2,948,000)	[14]	(4,896,000)		29,358,000	[14]	(8,774,000)	[14]
Adjustments | Funds Consolidation | Consolidated Funds
Revenues
Total revenues	[14]	(1,135,000)		(2,431,000)		(4,650,000)		(8,239,000)
Expenses
Total expenses	[14]	$ (494,000)		$ (2,516,000)		$ (4,793,000)		$ (6,229,000)

[1] Economic Income (Loss) presents expenses reimbursed from clients and affiliates within their respective expense category but is included as a part of revenues under US GAAP.

[2] Economic Income (Loss) presents underwriting expenses net of investment banking revenues.

[3] Economic Income (Loss) brokerage revenues included net securities borrowed and securities loaned activities which are shown gross in interest income and interest expense for US GAAP.

[4] Economic Income (Loss) recognizes gains and losses on investments held as part of the Company's facilitation and trading business within brokerage revenues as these investments are directly related to the markets business activities.

[5] Economic Income (Loss) presents revenues net of fund start-up costs and distribution fees paid to agents.

[6] Economic Income (Loss) recognizes the Company's proportionate share of management and incentive fees and associated share of expenses on a gross basis for certain real estate operating entities, the healthcare royalty business and the activist business. Additionally, carried interest, which the Company applies an equity ownership model to, is recorded in other income (loss) for US GAAP and is shown as incentive income for Economic Income (Loss).

[7] Economic Income (Loss) recognizes Company income from proprietary trading (including interest and dividends) for which the majority of this activity is shown in other income (loss) for US GAAP reporting.

[8] Economic Income (Loss) recognizes underwriting income from the Company's insurance related activities, net of expenses, within other revenue. The costs are recorded within expenses for US GAAP reporting.

[9] Economic Income (Loss) presents certain payments to associated banking partners as compensation rather than non-compensation expenses.

[10] Economic Income (Loss) presents US GAAP expenses as either Fixed non-compensation or Variable non-compensation expenses. The Company also presents US GAAP Income (loss) attributable to non-controlling interests within total other expenses for Economic Income (Loss).

[11] Economic Income (Loss) excludes the amortization of discount on convertible debt.

[12] Economic Income (Loss) excludes acquisition related adjustments as management does not consider these items when evaluating the performance of the Company.

[13] Economic Income (Loss) excludes goodwill and intangible impairment.

[14] The impacts of consolidation and the related elimination entries of the Consolidated Funds are not included in Economic Income (Loss). Adjustments to reconcile to US GAAP net income (loss) included elimination of incentive income and management fees earned from the Consolidated Funds and addition of investment fund expenses excluding management fees paid, investment fund revenues and investment income (loss).