BUSINESS SEGMENTS - Schedule of reportable segments (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021
Segment Reporting Information [Line Items]
Services and fees	$ 266,485	$ 301,497	$ 678,065	$ 857,109
Trading income (losses) and fair value adjustments on loans	12,154	18,197	(280,163)	317,818
Interest income - Loans and securities lending	57,594	26,869	182,855	89,280
Sale of goods	4,130	34,959	7,895	54,244
Total revenues	340,363	381,522	588,652	1,318,451
Direct cost of services	(44,523)	(18,019)	(73,959)	(41,435)
Cost of goods sold	(3,089)	(12,442)	(7,334)	(21,394)
Selling, general and administrative expenses	(163,727)	(244,218)	(506,062)	(635,484)
Restructuring charge	(8,016)	0	(8,016)	0
Interest expense - Securities lending and loan participations sold	(17,447)	(10,097)	(43,757)	(40,269)
Depreciation and amortization			(26,526)	(19,066)
Operating income (loss)	103,561	96,746	(50,476)	579,869
Corporate and other expenses	(19,832)	(17,987)	(44,368)	(42,007)
Interest income	686	70	1,253	175
Change in fair value of financial instruments and other	(574)	1,758	9,728	8,267
(Loss) income from equity investments	(91)	1,149	3,285	1,172
Interest expense	(34,587)	(25,372)	(96,787)	(66,014)
Income (loss) before income taxes	68,995	74,351	(132,997)	523,469
(Provision for) benefit from income taxes	(16,350)	(22,693)	39,858	(140,113)
Net income (loss)	52,645	51,658	(93,139)	383,356
Net income attributable to noncontrolling interests and redeemable noncontrolling interests	4,808	1,108	9,245	2,474
Net income (loss) attributable to B. Riley Financial, Inc.	47,837	50,550	(102,384)	380,882
Preferred stock dividends	2,002	1,929	6,006	5,467
Net income (loss) available to common shareholders	45,835	48,621	(108,390)	375,415
Net income (loss) available to common shareholders	45,835	48,621	(108,390)	375,415
Operating Segments
Segment Reporting Information [Line Items]
Operating income (loss)	123,393	114,733	(6,108)	621,876
Capital Markets Segment
Segment Reporting Information [Line Items]
Interest income - Loans and securities lending	55,054	26,869	178,879	89,280
Total revenues	179,398	178,653	145,366	832,440
Capital Markets Segment | Operating Segments
Segment Reporting Information [Line Items]
Services and fees	113,217	134,849	249,727	431,825
Trading income (losses) and fair value adjustments on loans	11,127	16,935	(283,240)	311,335
Interest income - Loans and securities lending	55,054	26,869	178,879	89,280
Total revenues	179,398	178,653	145,366	832,440
Selling, general and administrative expenses	(35,673)	(80,152)	(115,655)	(231,765)
Interest expense - Securities lending and loan participations sold	(17,447)	(10,097)	(43,757)	(40,269)
Depreciation and amortization	(2,174)	(514)	(6,271)	(1,526)
Operating income (loss)	124,104	87,890	(20,317)	558,880
Wealth Management Segment
Segment Reporting Information [Line Items]
Interest income - Loans and securities lending	0	0	0	0
Total revenues	48,172	118,834	188,040	277,041
Restructuring charge			(4,107)
Wealth Management Segment | Operating Segments
Segment Reporting Information [Line Items]
Services and fees	47,145	117,572	184,963	270,558
Trading income (losses) and fair value adjustments on loans	1,027	1,262	3,077	6,483
Total revenues	48,172	118,834	188,040	277,041
Selling, general and administrative expenses	(52,302)	(110,157)	(206,438)	(260,331)
Restructuring charge	(4,106)	0	(4,106)	0
Depreciation and amortization	(1,261)	(2,093)	(4,402)	(6,832)
Operating income (loss)	(9,497)	6,584	(26,906)	9,878
Auction and Liquidation Segment
Segment Reporting Information [Line Items]
Interest income - Loans and securities lending	2,540	0	3,976	0
Sale of goods	2,550	34,327	2,550	52,162
Total revenues	7,039	37,072	14,318	67,799
Auction and Liquidation Segment | Operating Segments
Segment Reporting Information [Line Items]
Services and fees	1,949	2,745	7,792	15,637
Interest income - Loans and securities lending	2,540	0	3,976	0
Sale of goods	2,550	34,327	2,550	52,162
Total revenues	7,039	37,072	14,318	67,799
Direct cost of services	(2,999)	(13,622)	(6,630)	(27,742)
Cost of goods sold	(1,235)	(11,999)	(1,235)	(19,578)
Selling, general and administrative expenses	(2,228)	(5,153)	(6,225)	(9,719)
Operating income (loss)	577	6,298	228	10,760
Financial Consulting Segment
Segment Reporting Information [Line Items]
Interest income - Loans and securities lending	0	0	0	0
Total revenues	22,835	21,291	73,081	66,435
Financial Consulting Segment | Operating Segments
Segment Reporting Information [Line Items]
Services and fees	22,835	21,291	73,081	66,435
Selling, general and administrative expenses	(20,056)	(18,436)	(60,947)	(55,896)
Depreciation and amortization	(75)	(86)	(234)	(273)
Operating income (loss)	2,704	2,769	11,900	10,266
Principal Investments- Communications and Other Segment
Segment Reporting Information [Line Items]
Interest income - Loans and securities lending	0	0	0	0
Sale of goods		631		2,081
Total revenues	77,896	19,300	153,093	59,475
Restructuring charge			(3,909)
Principal Investments- Communications and Other Segment | Operating Segments
Segment Reporting Information [Line Items]
Services and fees	76,316	18,669	147,748	57,394
Sale of goods	1,580	631	5,345	2,081
Total revenues	77,896	19,300	153,093	59,475
Direct cost of services	(41,524)	(4,397)	(67,329)	(13,693)
Cost of goods sold	(1,854)	(443)	(6,099)	(1,816)
Selling, general and administrative expenses	(22,267)	(5,458)	(44,103)	(15,096)
Restructuring charge	(3,910)	0	(3,910)	0
Depreciation and amortization	(6,435)	(2,496)	(13,255)	(7,558)
Operating income (loss)	1,906	6,506	18,397	21,312
Brands Segment
Segment Reporting Information [Line Items]
Interest income - Loans and securities lending	0	0	0	0
Total revenues	5,023	6,372	14,754	15,261
Brands Segment | Operating Segments
Segment Reporting Information [Line Items]
Services and fees	5,023	6,372	14,754	15,261
Selling, general and administrative expenses	(845)	(972)	(2,419)	(2,338)
Depreciation and amortization	(579)	(714)	(1,745)	(2,143)
Operating income (loss)	$ 3,599	$ 4,686	$ 10,590	$ 10,780