REVENUE FROM CONTRACTS WITH CUSTOMERS - Schedule of revenues from contracts with customers (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021
Revenue from External Customer [Line Items]
Total revenues from contracts with customers	$ 180,435	$ 270,791	$ 380,137	$ 560,043
Interest income - Loans and securities lending	63,835	25,491	125,261	62,411
Trading (losses) gains on investments	(212,965)	33,359	(292,293)	289,575
Fair value adjustment on loans	(10,962)	(680)	(24)	10,046
Other	22,357	7,809	35,208	14,854
Total revenues	42,700	336,770	248,289	936,929
Sale of goods	1,887	12,457	3,765	19,285
Capital Markets Segment
Revenue from External Customer [Line Items]
Total revenues from contracts with customers	49,328	120,483	105,446	285,980
Interest income - Loans and securities lending	62,399	25,491	123,825	62,411
Trading (losses) gains on investments	(214,493)	30,577	(294,343)	284,354
Fair value adjustment on loans	(10,962)	(680)	(24)	10,046
Other	18,098	5,514	31,064	10,996
Total revenues	(95,630)	181,385	(34,032)	653,787
Wealth Management Segment
Revenue from External Customer [Line Items]
Total revenues from contracts with customers	56,602	85,149	133,674	149,128
Interest income - Loans and securities lending	0	0	0	0
Trading (losses) gains on investments	1,528	2,865	2,050	5,221
Fair value adjustment on loans	0	0	0	0
Other	4,259	2,295	4,144	3,858
Total revenues	62,389	90,309	139,868	158,207
Auction and Liquidation Segment
Revenue from External Customer [Line Items]
Total revenues from contracts with customers	2,488	17,277	5,843	30,727
Interest income - Loans and securities lending	1,436	0	1,436	0
Trading (losses) gains on investments	0	0	0	0
Fair value adjustment on loans	0	0	0	0
Other	0	0	0	0
Total revenues	3,924	17,277	7,279	30,727
Sale of goods		11,743		17,835
Financial Consulting Segment
Revenue from External Customer [Line Items]
Total revenues from contracts with customers	24,310	23,735	50,246	45,144
Interest income - Loans and securities lending	0	0	0	0
Trading (losses) gains on investments	0	0	0	0
Fair value adjustment on loans	0	0	0	0
Other	0		0	0
Total revenues	24,310	23,735	50,246	45,144
Principal Investments- Communications and Other Segment
Revenue from External Customer [Line Items]
Total revenues from contracts with customers	42,533	19,646	75,197	40,175
Interest income - Loans and securities lending	0	0	0	0
Trading (losses) gains on investments	0	0	0	0
Fair value adjustment on loans	0	0	0	0
Other	0	0	0	0
Total revenues	42,533	19,646	75,197	40,175
Sale of goods		714		1,450
Brands Segment
Revenue from External Customer [Line Items]
Total revenues from contracts with customers	5,174	4,501	9,731	8,889
Interest income - Loans and securities lending	0	0	0	0
Trading (losses) gains on investments		(83)	0	0
Fair value adjustment on loans	0	0	0	0
Other	0	0	0	0
Total revenues	5,174	4,418	9,731	8,889
Corporate finance, consulting and investment banking fees
Revenue from External Customer [Line Items]
Total revenues from contracts with customers	51,119	121,737	109,762	282,233
Corporate finance, consulting and investment banking fees | Capital Markets Segment
Revenue from External Customer [Line Items]
Total revenues from contracts with customers	35,473	107,224	77,146	254,293
Corporate finance, consulting and investment banking fees | Wealth Management Segment
Revenue from External Customer [Line Items]
Total revenues from contracts with customers	0	0	0	0
Corporate finance, consulting and investment banking fees | Auction and Liquidation Segment
Revenue from External Customer [Line Items]
Total revenues from contracts with customers	0	0	0	0
Corporate finance, consulting and investment banking fees | Financial Consulting Segment
Revenue from External Customer [Line Items]
Total revenues from contracts with customers	15,646	14,513	32,616	27,940
Corporate finance, consulting and investment banking fees | Principal Investments- Communications and Other Segment
Revenue from External Customer [Line Items]
Total revenues from contracts with customers	0	0	0	0
Corporate finance, consulting and investment banking fees | Brands Segment
Revenue from External Customer [Line Items]
Total revenues from contracts with customers	0	0	0	0
Wealth and asset management fees
Revenue from External Customer [Line Items]
Total revenues from contracts with customers	55,810	69,011	122,432	122,406
Wealth and asset management fees | Capital Markets Segment
Revenue from External Customer [Line Items]
Total revenues from contracts with customers	2,519	1,994	4,919	4,878
Wealth and asset management fees | Wealth Management Segment
Revenue from External Customer [Line Items]
Total revenues from contracts with customers	53,291	67,017	117,513	117,528
Wealth and asset management fees | Auction and Liquidation Segment
Revenue from External Customer [Line Items]
Total revenues from contracts with customers	0	0	0	0
Wealth and asset management fees | Financial Consulting Segment
Revenue from External Customer [Line Items]
Total revenues from contracts with customers	0	0	0	0
Wealth and asset management fees | Principal Investments- Communications and Other Segment
Revenue from External Customer [Line Items]
Total revenues from contracts with customers	0	0	0	0
Wealth and asset management fees | Brands Segment
Revenue from External Customer [Line Items]
Total revenues from contracts with customers	0	0	0	0
Commissions, fees and reimbursed expenses
Revenue from External Customer [Line Items]
Total revenues from contracts with customers	25,799	43,368	63,015	87,420
Commissions, fees and reimbursed expenses | Capital Markets Segment
Revenue from External Customer [Line Items]
Total revenues from contracts with customers	11,336	11,265	23,381	26,809
Commissions, fees and reimbursed expenses | Wealth Management Segment
Revenue from External Customer [Line Items]
Total revenues from contracts with customers	3,311	18,132	16,161	31,600
Commissions, fees and reimbursed expenses | Auction and Liquidation Segment
Revenue from External Customer [Line Items]
Total revenues from contracts with customers	2,488	4,749	5,843	11,807
Commissions, fees and reimbursed expenses | Financial Consulting Segment
Revenue from External Customer [Line Items]
Total revenues from contracts with customers	8,664	9,222	17,630	17,204
Commissions, fees and reimbursed expenses | Principal Investments- Communications and Other Segment
Revenue from External Customer [Line Items]
Total revenues from contracts with customers	0	0	0	0
Commissions, fees and reimbursed expenses | Brands Segment
Revenue from External Customer [Line Items]
Total revenues from contracts with customers	0	0	0	0
Subscription services
Revenue from External Customer [Line Items]
Total revenues from contracts with customers	37,809	17,255	65,622	34,499
Subscription services | Capital Markets Segment
Revenue from External Customer [Line Items]
Total revenues from contracts with customers	0	0	0	0
Subscription services | Wealth Management Segment
Revenue from External Customer [Line Items]
Total revenues from contracts with customers	0	0	0	0
Subscription services | Auction and Liquidation Segment
Revenue from External Customer [Line Items]
Total revenues from contracts with customers	0	0	0	0
Subscription services | Financial Consulting Segment
Revenue from External Customer [Line Items]
Total revenues from contracts with customers	0	0	0	0
Subscription services | Principal Investments- Communications and Other Segment
Revenue from External Customer [Line Items]
Total revenues from contracts with customers	37,809	17,255	65,622	34,499
Subscription services | Brands Segment
Revenue from External Customer [Line Items]
Total revenues from contracts with customers	0	0	0	0
Advertising, licensing and other
Revenue from External Customer [Line Items]
Total revenues from contracts with customers	9,898	18,636	19,306	32,400
Advertising, licensing and other | Capital Markets Segment
Revenue from External Customer [Line Items]
Total revenues from contracts with customers	0	0	0	0
Advertising, licensing and other | Wealth Management Segment
Revenue from External Customer [Line Items]
Total revenues from contracts with customers	0	0	0	0
Advertising, licensing and other | Auction and Liquidation Segment
Revenue from External Customer [Line Items]
Total revenues from contracts with customers	0	11,744	0	17,835
Advertising, licensing and other | Financial Consulting Segment
Revenue from External Customer [Line Items]
Total revenues from contracts with customers	0	0	0	0
Advertising, licensing and other | Principal Investments- Communications and Other Segment
Revenue from External Customer [Line Items]
Total revenues from contracts with customers	4,724	2,391	9,575	5,676
Sale of goods	1,887		3,765
Advertising, licensing and other | Brands Segment
Revenue from External Customer [Line Items]
Total revenues from contracts with customers	$ 5,174	4,501	$ 9,731	8,889
Service contract revenues
Revenue from External Customer [Line Items]
Total revenues from contracts with customers		784		1,085
Service contract revenues | Capital Markets Segment
Revenue from External Customer [Line Items]
Total revenues from contracts with customers		0		0
Service contract revenues | Wealth Management Segment
Revenue from External Customer [Line Items]
Total revenues from contracts with customers		0		0
Service contract revenues | Auction and Liquidation Segment
Revenue from External Customer [Line Items]
Total revenues from contracts with customers		784		1,085
Service contract revenues | Financial Consulting Segment
Revenue from External Customer [Line Items]
Total revenues from contracts with customers		0		0
Service contract revenues | Principal Investments- Communications and Other Segment
Revenue from External Customer [Line Items]
Total revenues from contracts with customers		0		0
Service contract revenues | Brands Segment
Revenue from External Customer [Line Items]
Total revenues from contracts with customers		$ 0		$ 0