BUSINESS SEGMENTS - Schedule of reportable segments (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021
Segment Reporting Information [Line Items]
Services and fees	$ 200,905	$ 266,143	$ 411,580	$ 555,612
Trading (losses) income and fair value adjustments on loans	(223,927)	32,679	(292,317)	299,621
Interest income - Loans and securities lending	63,835	25,491	125,261	62,411
Sale of goods	1,887	12,457	3,765	19,285
Total revenues	42,700	336,770	248,289	936,929
Direct cost of services	(17,785)	(12,094)	(29,436)	(23,416)
Cost of goods sold	(1,994)	(3,626)	(4,245)	(8,952)
Selling, general and administrative expenses	(167,136)	(199,922)	(342,335)	(391,266)
Interest expense - Securities lending and loan participations sold	(14,544)	(10,983)	(26,310)	(30,172)
Depreciation and amortization			(15,809)	(12,924)
Operating (loss) income	(158,759)	110,145	(154,037)	483,123
Corporate and other expenses	(9,358)	(11,822)	(24,536)	(24,020)
Interest income	500	56	567	105
Change in fair value of financial instruments and other	4,321	6,509	10,302	6,509
(Loss) income from equity investments	(3,399)	(852)	3,376	23
Interest expense	(31,764)	(20,856)	(62,200)	(40,642)
(Loss) income before income taxes	(189,101)	95,002	(201,992)	449,118
Benefit from (provision for) income taxes	52,513	(19,902)	56,208	(117,420)
Net (loss) income	(136,588)	75,100	(145,784)	331,698
Net income (loss) attributable to noncontrolling interests and redeemable noncontrolling interests	3,571	(576)	4,437	1,366
Net (loss) income attributable to B. Riley Financial, Inc.	(140,159)	75,676	(150,221)	330,332
Preferred stock dividends	2,002	1,789	4,004	3,538
Net (loss) income available to common shareholders	(142,161)	73,887	(154,225)	326,794
Net (loss) income available to common shareholders	(142,161)	73,887	(154,225)	326,794
Operating Segments
Segment Reporting Information [Line Items]
Operating (loss) income	(149,401)	121,967	(129,501)	507,143
Capital Markets Segment
Segment Reporting Information [Line Items]
Interest income - Loans and securities lending	62,399	25,491	123,825	62,411
Total revenues	(95,630)	181,385	(34,032)	653,787
Capital Markets Segment | Operating Segments
Segment Reporting Information [Line Items]
Services and fees	67,426	125,997	136,510	296,976
Trading (losses) income and fair value adjustments on loans	(225,455)	29,897	(294,367)	294,400
Interest income - Loans and securities lending	62,399	25,491	123,825	62,411
Total revenues	(95,630)	181,385	(34,032)	653,787
Selling, general and administrative expenses	(45,865)	(65,473)	(79,982)	(151,613)
Interest expense - Securities lending and loan participations sold	(14,544)	(10,983)	(26,310)	(30,172)
Depreciation and amortization	(2,204)	(247)	(4,097)	(1,012)
Operating (loss) income	(158,243)	104,682	(144,421)	470,990
Wealth Management Segment
Segment Reporting Information [Line Items]
Interest income - Loans and securities lending	0	0	0	0
Total revenues	62,389	90,309	139,868	158,207
Wealth Management Segment | Operating Segments
Segment Reporting Information [Line Items]
Services and fees	60,861	87,444	137,818	152,986
Trading (losses) income and fair value adjustments on loans	1,528	2,865	2,050	5,221
Total revenues	62,389	90,309	139,868	158,207
Selling, general and administrative expenses	(68,394)	(88,702)	(154,136)	(150,174)
Depreciation and amortization	(1,308)	(2,340)	(3,141)	(4,739)
Operating (loss) income	(7,313)	(733)	(17,409)	3,294
Auction and Liquidation Segment
Segment Reporting Information [Line Items]
Interest income - Loans and securities lending	1,436	0	1,436	0
Sale of goods		11,743		17,835
Total revenues	3,924	17,277	7,279	30,727
Auction and Liquidation Segment | Operating Segments
Segment Reporting Information [Line Items]
Services and fees	2,488	5,534	5,843	12,892
Interest income - Loans and securities lending	1,436	0	1,436	0
Sale of goods	0	11,743	0	17,835
Total revenues	3,924	17,277	7,279	30,727
Direct cost of services	(1,296)	(7,540)	(3,631)	(14,120)
Cost of goods sold	0	(3,105)	0	(7,579)
Selling, general and administrative expenses	(2,177)	(3,077)	(3,997)	(4,566)
Operating (loss) income	451	3,555	(349)	4,462
Financial Consulting Segment
Segment Reporting Information [Line Items]
Interest income - Loans and securities lending	0	0	0	0
Total revenues	24,310	23,735	50,246	45,144
Financial Consulting Segment | Operating Segments
Segment Reporting Information [Line Items]
Services and fees	24,310	23,735	50,246	45,144
Selling, general and administrative expenses	(19,948)	(19,471)	(40,891)	(37,460)
Depreciation and amortization	(78)	(89)	(159)	(187)
Operating (loss) income	4,284	4,175	9,196	7,497
Principal Investments- Communications and Other Segment
Segment Reporting Information [Line Items]
Interest income - Loans and securities lending	0	0	0	0
Sale of goods		714		1,450
Total revenues	42,533	19,646	75,197	40,175
Principal Investments- Communications and Other Segment | Operating Segments
Segment Reporting Information [Line Items]
Services and fees	40,646	18,932	71,432	38,725
Sale of goods	1,887	714	3,765	1,450
Total revenues	42,533	19,646	75,197	40,175
Direct cost of services	(16,489)	(4,554)	(25,805)	(9,296)
Cost of goods sold	(1,994)	(521)	(4,245)	(1,373)
Selling, general and administrative expenses	(12,808)	(4,768)	(21,836)	(9,638)
Depreciation and amortization	(3,595)	(2,528)	(6,820)	(5,062)
Operating (loss) income	7,647	7,275	16,491	14,806
Brands Segment
Segment Reporting Information [Line Items]
Interest income - Loans and securities lending	0	0	0	0
Total revenues	5,174	4,418	9,731	8,889
Brands Segment | Operating Segments
Segment Reporting Information [Line Items]
Services and fees	5,174	4,501	9,731	8,889
Trading (losses) income and fair value adjustments on loans	0	(83)	0	0
Total revenues	5,174	4,418	9,731	8,889
Selling, general and administrative expenses	(818)	(690)	(1,574)	(1,366)
Depreciation and amortization	(583)	(715)	(1,166)	(1,429)
Operating (loss) income	$ 3,773	$ 3,013	$ 6,991	$ 6,094