BUSINESS SEGMENTS - Schedule of reportable segments (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Segment Reporting Information [Line Items]
Services and fees	$ 210,675	$ 289,469
Trading (losses) income and fair value adjustments on loans	(68,390)	266,942
Interest income - Loans and securities lending	61,426	36,920
Sale of goods	1,878	6,828
Total revenues	205,589	600,159
Direct cost of services	(11,651)	(11,322)
Cost of goods sold	(2,251)	(5,326)
Selling, general and administrative expenses	(175,199)	(191,344)
Interest expense - Securities lending and loan participations sold	(11,766)	(19,189)
Depreciation and amortization	(7,848)	(6,759)
Operating income	4,722	372,978
Corporate and other expenses	(15,178)	(12,198)
Interest income	67	49
Change in fair value of financial instruments and other	5,981	0
Income from equity investments	6,775	875
Interest expense	(30,436)	(19,786)
(Loss) income before income taxes	(12,891)	354,116
Benefit from (provision for) income taxes	3,695	(97,518)
Net (loss) income	(9,196)	256,598
Net income attributable to noncontrolling interests	866	1,942
Net (loss) income attributable to B. Riley Financial, Inc.	(10,062)	254,656
Preferred stock dividends	2,002	1,749
Net (loss) income available to common shareholders	(12,064)	252,907
Net (loss) income available to common shareholders	(12,064)	252,907
Operating Segments
Segment Reporting Information [Line Items]
Operating income	19,900	385,176
Capital Markets Segment
Segment Reporting Information [Line Items]
Interest income - Loans and securities lending	61,426	36,920
Total revenues	61,598	472,402
Capital Markets Segment | Operating Segments
Segment Reporting Information [Line Items]
Services and fees	69,084	170,979
Trading (losses) income and fair value adjustments on loans	(68,912)	264,503
Interest income - Loans and securities lending	61,426	36,920
Total revenues	61,598	472,402
Selling, general and administrative expenses	(34,117)	(86,140)
Interest expense - Securities lending and loan participations sold	(11,766)	(19,189)
Depreciation and amortization	(1,893)	(765)
Operating income	13,822	366,308
Wealth Management Segment
Segment Reporting Information [Line Items]
Interest income - Loans and securities lending	0	0
Total revenues	77,479	67,898
Wealth Management Segment | Operating Segments
Segment Reporting Information [Line Items]
Services and fees	76,957	65,542
Trading (losses) income and fair value adjustments on loans	522	2,356
Total revenues	77,479	67,898
Selling, general and administrative expenses	(85,742)	(61,472)
Depreciation and amortization	(1,833)	(2,399)
Operating income	(10,096)	4,027
Auction and Liquidation Segment
Segment Reporting Information [Line Items]
Interest income - Loans and securities lending	0	0
Sale of goods		6,092
Total revenues	3,355	13,450
Auction and Liquidation Segment | Operating Segments
Segment Reporting Information [Line Items]
Services and fees	3,355	7,358
Sale of goods	0	6,092
Total revenues	3,355	13,450
Direct cost of services	(2,335)	(6,580)
Cost of goods sold	0	(4,474)
Selling, general and administrative expenses	(1,820)	(1,489)
Operating income	(800)	907
Financial Consulting Segment
Segment Reporting Information [Line Items]
Interest income - Loans and securities lending	0	0
Total revenues	25,936	21,409
Financial Consulting Segment | Operating Segments
Segment Reporting Information [Line Items]
Services and fees	25,936	21,409
Selling, general and administrative expenses	(20,943)	(17,989)
Depreciation and amortization	(81)	(98)
Operating income	4,912	3,322
Principal Investments- Communications and Other Segment
Segment Reporting Information [Line Items]
Interest income - Loans and securities lending	0	0
Sale of goods		736
Total revenues	32,664	20,529
Principal Investments- Communications and Other Segment | Operating Segments
Segment Reporting Information [Line Items]
Services and fees	30,786	19,793
Sale of goods	1,878	736
Total revenues	32,664	20,529
Direct cost of services	(9,316)	(4,742)
Cost of goods sold	(2,251)	(852)
Selling, general and administrative expenses	(9,028)	(4,870)
Depreciation and amortization	(3,225)	(2,534)
Operating income	8,844	7,531
Brands Segment
Segment Reporting Information [Line Items]
Interest income - Loans and securities lending	0	0
Total revenues	4,557	4,471
Brands Segment | Operating Segments
Segment Reporting Information [Line Items]
Services and fees	4,557	4,388
Trading (losses) income and fair value adjustments on loans	0	83
Total revenues	4,557	4,471
Selling, general and administrative expenses	(756)	(676)
Depreciation and amortization	(583)	(714)
Operating income	$ 3,218	$ 3,081