GOODWILL AND OTHER INTANGIBLE ASSETS - Schedule of carrying amount of goodwill (Details) $ in Thousands	6 Months Ended
	Jun. 30, 2022 USD ($)
Goodwill [Roll Forward]
Beginning Balance	$ 250,568
Acquisition of other businesses	143,763
Ending Balance	394,331
Capital Markets Segment
Goodwill [Roll Forward]
Beginning Balance	51,338
Acquisition of other businesses	110,512
Ending Balance	161,850
Wealth Management Segment
Goodwill [Roll Forward]
Beginning Balance	51,195
Acquisition of other businesses	0
Ending Balance	51,195
Auction and Liquidation Segment
Goodwill [Roll Forward]
Beginning Balance	1,975
Acquisition of other businesses	0
Ending Balance	1,975
Financial Consulting Segment
Goodwill [Roll Forward]
Beginning Balance	23,680
Acquisition of other businesses	0
Ending Balance	23,680
Principal Investments- Communications and Other Segment
Goodwill [Roll Forward]
Beginning Balance	122,380
Acquisition of other businesses	33,251
Ending Balance	$ 155,631