SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Schedule of financial assets and liabilities measured on recurring basis (Details) - USD ($) $ in Thousands	Sep. 30, 2022	Dec. 31, 2021
Assets:
Funds held in trust account	$ 173,216	$ 345,024
Securities and other investments owned:
Total securities and other investments owned	1,071,858	1,394,967
Loans receivable, at fair value	814,715	873,186
Total assets measured at fair value	2,059,789	2,613,177
Securities sold not yet purchased:
Total securities sold not yet purchased	17,751	28,623
Mandatorily redeemable noncontrolling interests issued after November 5, 2003	4,322	4,506
Warrant liabilities	633	12,938
Contingent consideration	29,578	0
Total liabilities measured at fair value	52,284	46,067
Quoted prices in active markets for identical assets (Level 1)
Assets:
Funds held in trust account	173,216	345,024
Securities and other investments owned:
Total securities and other investments owned	717,092	1,007,180
Loans receivable, at fair value	0	0
Total assets measured at fair value	890,308	1,352,204
Securities sold not yet purchased:
Total securities sold not yet purchased	10,801	20,302
Mandatorily redeemable noncontrolling interests issued after November 5, 2003	0	0
Warrant liabilities	633	12,938
Contingent consideration	0
Total liabilities measured at fair value	11,434	33,240
Other observable inputs (Level 2)
Assets:
Funds held in trust account	0	0
Securities and other investments owned:
Total securities and other investments owned	15,410	10,238
Loans receivable, at fair value	0	0
Total assets measured at fair value	15,410	10,238
Securities sold not yet purchased:
Total securities sold not yet purchased	6,950	8,321
Mandatorily redeemable noncontrolling interests issued after November 5, 2003	0	0
Warrant liabilities	0	0
Contingent consideration	0
Total liabilities measured at fair value	6,950	8,321
Significant unobservable inputs (Level 3)
Assets:
Funds held in trust account	0	0
Securities and other investments owned:
Total securities and other investments owned	339,356	377,549
Loans receivable, at fair value	814,715	873,186
Total assets measured at fair value	1,154,071	1,250,735
Securities sold not yet purchased:
Total securities sold not yet purchased	0	0
Mandatorily redeemable noncontrolling interests issued after November 5, 2003	4,322	4,506
Warrant liabilities	0	0
Contingent consideration	29,578
Total liabilities measured at fair value	33,900	4,506
Equity securities
Securities and other investments owned:
Total securities and other investments owned	1,056,448	1,384,729
Securities sold not yet purchased:
Total securities sold not yet purchased	10,801	20,302
Equity securities | Quoted prices in active markets for identical assets (Level 1)
Securities and other investments owned:
Total securities and other investments owned	717,092	1,007,180
Securities sold not yet purchased:
Total securities sold not yet purchased	10,801	20,302
Equity securities | Other observable inputs (Level 2)
Securities and other investments owned:
Total securities and other investments owned	0	0
Securities sold not yet purchased:
Total securities sold not yet purchased	0	0
Equity securities | Significant unobservable inputs (Level 3)
Securities and other investments owned:
Total securities and other investments owned	339,356	377,549
Securities sold not yet purchased:
Total securities sold not yet purchased	0	0
Corporate bonds
Securities and other investments owned:
Total securities and other investments owned	6,761	7,632
Securities sold not yet purchased:
Total securities sold not yet purchased	6,264	6,327
Corporate bonds | Quoted prices in active markets for identical assets (Level 1)
Securities and other investments owned:
Total securities and other investments owned	0	0
Securities sold not yet purchased:
Total securities sold not yet purchased	0	0
Corporate bonds | Other observable inputs (Level 2)
Securities and other investments owned:
Total securities and other investments owned	6,761	7,632
Securities sold not yet purchased:
Total securities sold not yet purchased	6,264	6,327
Corporate bonds | Significant unobservable inputs (Level 3)
Securities and other investments owned:
Total securities and other investments owned	0	0
Securities sold not yet purchased:
Total securities sold not yet purchased	0	0
Other fixed income securities
Securities and other investments owned:
Total securities and other investments owned	8,649	2,606
Securities sold not yet purchased:
Total securities sold not yet purchased	686	1,994
Other fixed income securities | Quoted prices in active markets for identical assets (Level 1)
Securities and other investments owned:
Total securities and other investments owned	0	0
Securities sold not yet purchased:
Total securities sold not yet purchased	0	0
Other fixed income securities | Other observable inputs (Level 2)
Securities and other investments owned:
Total securities and other investments owned	8,649	2,606
Securities sold not yet purchased:
Total securities sold not yet purchased	686	1,994
Other fixed income securities | Significant unobservable inputs (Level 3)
Securities and other investments owned:
Total securities and other investments owned	0	0
Securities sold not yet purchased:
Total securities sold not yet purchased	$ 0	$ 0