REVENUE FROM CONTRACTS WITH CUSTOMERS - Schedule of revenues from contracts with customers (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021
Revenue from External Customer [Line Items]
Total revenues from contracts with customers	$ 209,712	$ 326,609	$ 589,849	$ 886,653
Interest income - Loans and securities lending	57,594	26,869	182,855	89,280
Trading gains on investments	16,198	19,446	(276,095)	309,022
Fair value adjustment on loans	(4,044)	(1,249)	(4,068)	8,796
Other	60,903	9,847	96,111	24,700
Total revenues	340,363	381,522	588,652	1,318,451
Sale of goods	4,130	34,959	7,895	54,244
Capital Markets Segment
Revenue from External Customer [Line Items]
Total revenues from contracts with customers	53,409	127,616	158,855	413,597
Interest income - Loans and securities lending	55,054	26,869	178,879	89,280
Trading gains on investments	15,171	18,184	(279,172)	302,539
Fair value adjustment on loans	(4,044)	(1,249)	(4,068)	8,796
Other	59,808	7,233	90,872	18,228
Total revenues	179,398	178,653	145,366	832,440
Wealth Management Segment
Revenue from External Customer [Line Items]
Total revenues from contracts with customers	46,050	114,958	179,724	264,086
Interest income - Loans and securities lending	0	0	0	0
Trading gains on investments	1,027	1,262	3,077	6,483
Fair value adjustment on loans	0	0	0	0
Other	1,095	2,614	5,239	6,472
Total revenues	48,172	118,834	188,040	277,041
Auction and Liquidation Segment
Revenue from External Customer [Line Items]
Total revenues from contracts with customers	4,499	37,072	10,342	67,799
Interest income - Loans and securities lending	2,540	0	3,976	0
Trading gains on investments	0	0	0	0
Fair value adjustment on loans	0	0	0	0
Other	0	0	0	0
Total revenues	7,039	37,072	14,318	67,799
Sale of goods	2,550	34,327	2,550	52,162
Financial Consulting Segment
Revenue from External Customer [Line Items]
Total revenues from contracts with customers	22,835	21,291	73,081	66,435
Interest income - Loans and securities lending	0	0	0	0
Trading gains on investments	0	0	0	0
Fair value adjustment on loans	0	0	0	0
Other	0		0	0
Total revenues	22,835	21,291	73,081	66,435
Principal Investments- Communications and Other Segment
Revenue from External Customer [Line Items]
Total revenues from contracts with customers	77,896	19,300	153,093	59,475
Interest income - Loans and securities lending	0	0	0	0
Trading gains on investments	0	0	0	0
Fair value adjustment on loans	0	0	0	0
Other	0	0	0	0
Total revenues	77,896	19,300	153,093	59,475
Sale of goods		631		2,081
Brands Segment
Revenue from External Customer [Line Items]
Total revenues from contracts with customers	5,023	6,372	14,754	15,261
Interest income - Loans and securities lending	0	0	0	0
Trading gains on investments		0	0	0
Fair value adjustment on loans	0	0	0	0
Other	0	0	0	0
Total revenues	5,023	6,372	14,754	15,261
Corporate finance, consulting and investment banking fees
Revenue from External Customer [Line Items]
Total revenues from contracts with customers	53,644	128,394	163,406	410,627
Corporate finance, consulting and investment banking fees | Capital Markets Segment
Revenue from External Customer [Line Items]
Total revenues from contracts with customers	41,302	116,044	118,448	370,337
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	12,342	12,350	44,958	40,290
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	47,602	87,258	170,034	209,664
Wealth and asset management fees | Capital Markets Segment
Revenue from External Customer [Line Items]
Total revenues from contracts with customers	3,280	679	8,199	5,557
Wealth and asset management fees | Wealth Management Segment
Revenue from External Customer [Line Items]
Total revenues from contracts with customers	44,322	86,579	161,835	204,107
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	22,997	50,953	86,012	138,374
Commissions, fees and reimbursed expenses | Capital Markets Segment
Revenue from External Customer [Line Items]
Total revenues from contracts with customers	8,827	10,893	32,208	37,703
Commissions, fees and reimbursed expenses | Wealth Management Segment
Revenue from External Customer [Line Items]
Total revenues from contracts with customers	1,728	28,379	17,889	59,979
Commissions, fees and reimbursed expenses | Auction and Liquidation Segment
Revenue from External Customer [Line Items]
Total revenues from contracts with customers	1,949	2,740	7,792	14,547
Commissions, fees and reimbursed expenses | Financial Consulting Segment
Revenue from External Customer [Line Items]
Total revenues from contracts with customers	10,493	8,941	28,123	26,145
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	70,152	16,303	135,774	50,802
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	70,152	16,303	135,774	50,802
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	15,317	43,696	34,623	76,096
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	2,550	34,327	2,550	52,162
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	7,744	2,997	17,319	8,673
Sale of goods	1,580		5,345
Advertising, licensing and other | Brands Segment
Revenue from External Customer [Line Items]
Total revenues from contracts with customers	$ 5,023	6,372	$ 14,754	15,261
Service contract revenues
Revenue from External Customer [Line Items]
Total revenues from contracts with customers		5		1,090
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		5		1,090
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