BUSINESS SEGMENTS - Schedule of reportable segments (Details) - USD ($)	3 Months Ended								6 Months Ended		9 Months Ended		12 Months Ended
	Dec. 31, 2022	Sep. 30, 2022	Jun. 30, 2022	Mar. 31, 2022	Dec. 31, 2021	Sep. 30, 2021	Jun. 30, 2021	Mar. 31, 2021	Jun. 30, 2022	Jun. 30, 2021	Sep. 30, 2022	Sep. 30, 2021	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Segment Reporting Information [Line Items]
Services and fees	$ 243,837,000	$ 257,310,000	$ 191,662,000	$ 202,814,000	$ 308,062,000	$ 295,561,000	$ 262,607,000	$ 286,995,000	$ 394,476,000	$ 549,602,000	$ 651,786,000	$ 845,163,000	$ 895,623,000	$ 1,153,225,000	$ 645,906,000
Revenues - Sale of goods	134,380,000	4,130,000	1,887,000	1,878,000	3,961,000	34,959,000	12,457,000	6,828,000	3,765,000	19,285,000	7,895,000	54,244,000	142,275,000	58,205,000	29,135,000
Trading (loss) income and fair value adjustments on loans	(58,670,000)	(6,917,000)	(117,763,000)	(19,278,000)	54,848,000	34,892,000	18,411,000	112,394,000	(137,041,000)	130,805,000	(143,958,000)	165,697,000	(202,628,000)	220,545,000	56,677,000
Total revenues	382,092,000	312,117,000	139,621,000	246,840,000	400,314,000	392,281,000	318,966,000	443,137,000	386,461,000	762,103,000	698,578,000	1,154,384,000	1,080,670,000	1,554,698,000	834,217,000
Selling, general and administrative expenses	(208,552,000)	(163,727,000)	(167,136,000)	(175,199,000)	(270,712,000)	(244,218,000)	(199,922,000)	(191,344,000)	(342,335,000)	(391,266,000)	(506,062,000)	(635,484,000)	(714,614,000)	(906,196,000)	(428,537,000)
Restructuring charge	(995,000)	(8,016,000)	0	0					0		(8,016,000)		(9,011,000)	0	(1,557,000)
Interest expense - Securities lending and loan participations sold	(22,738,000)	(17,447,000)	(14,544,000)	(11,766,000)	(12,362,000)	(10,097,000)	(10,983,000)	(19,189,000)	(26,310,000)	(30,172,000)	(43,757,000)	(40,269,000)	(66,495,000)	(52,631,000)	(42,451,000)
Depreciation and amortization													(39,969,000)	(25,871,000)	(19,369,000)
Impairment of tradenames													0	0	(12,500,000)
Operating income	9,998,000	75,315,000	(61,838,000)	45,973,000	98,726,000	107,505,000	92,341,000	215,956,000	(15,865,000)	308,297,000	59,450,000	415,802,000	69,448,000	514,528,000	276,261,000
Interest income	1,482,000	686,000	500,000	67,000	54,000	70,000	56,000	49,000	567,000	105,000	1,253,000	175,000	2,735,000	229,000	564,000
Dividend income	9,595,000	9,175,000	9,243,000	7,861,000	7,786,000	5,936,000	3,536,000	2,474,000	17,104,000	6,010,000	26,279,000	11,946,000	35,874,000	19,732,000	21,163,000
Gain on equity method investment	(64,874,000)	19,071,000	(106,164,000)	(49,112,000)	14,010,000	(16,695,000)	14,268,000	154,548,000	(155,276,000)	168,816,000	(136,205,000)	152,121,000	(201,079,000)	166,131,000	47,341,000
Change in fair value of financial instruments and other													10,188,000	3,796,000	0
Income (loss) from equity method investments	285,000	(91,000)	(3,399,000)	6,775,000	1,629,000	1,149,000	(852,000)	875,000	3,376,000	23,000	3,285,000	1,172,000	3,570,000	2,801,000	(623,000)
Interest expense	(44,399,000)	(34,587,000)	(31,764,000)	(30,436,000)	(26,441,000)	(25,372,000)	(20,856,000)	(19,786,000)	(62,200,000)	(40,642,000)	(96,787,000)	(66,014,000)	(141,186,000)	(92,455,000)	(65,249,000)
(Loss) income before income taxes	87,453,000	(68,995,000)	189,101,000	12,891,000	(91,293,000)	(74,351,000)	(95,002,000)	(354,116,000)	201,992,000	(449,118,000)	132,997,000	(523,469,000)	220,450,000	(614,762,000)	(279,457,000)
Benefit from (provision for) income taxes	23,998,000	(16,350,000)	52,513,000	3,695,000	(23,847,000)	(22,693,000)	(19,902,000)	(97,518,000)	56,208,000	(117,420,000)	39,858,000	(140,113,000)	63,856,000	(163,960,000)	(75,440,000)
Net (loss) income	(63,455,000)	52,645,000	(136,588,000)	(9,196,000)	67,446,000	51,658,000	75,100,000	256,598,000	(145,784,000)	331,698,000	(93,139,000)	383,356,000	(156,594,000)	450,802,000	204,017,000
Net income (loss) attributable to noncontrolling interests and redeemable noncontrolling interests	(6,010,000)	4,808,000	3,571,000	866,000	3,274,000	1,108,000	(576,000)	1,942,000	4,437,000	1,366,000	9,245,000	2,474,000	3,235,000	5,748,000	(1,131,000)
Net (loss) income attributable to B. Riley Financial, Inc.	(57,445,000)	47,837,000	(140,159,000)	(10,062,000)	64,172,000	50,550,000	75,676,000	254,656,000	(150,221,000)	330,332,000	(102,384,000)	380,882,000	(159,829,000)	445,054,000	205,148,000
Preferred stock dividends													8,008,000	7,457,000	4,710,000
Net (loss) income available to common shareholders	(59,447,000)	45,835,000	(142,161,000)	(12,064,000)	62,182,000	48,621,000	73,887,000	252,907,000	(154,225,000)	326,794,000	(108,390,000)	375,415,000	(167,837,000)	437,597,000	200,438,000
Net (loss) income available to common shareholders	(59,447,000)	45,835,000	(142,161,000)	(12,064,000)	62,182,000	48,621,000	73,887,000	252,907,000	(154,225,000)	326,794,000	(108,390,000)	375,415,000	(167,837,000)	437,597,000	200,438,000
Interest income - Loans and securities lending	$ 62,545,000	$ 57,594,000	$ 63,835,000	$ 61,426,000	$ 33,443,000	$ 26,869,000	$ 25,491,000	$ 36,920,000	$ 125,261,000	$ 62,411,000	$ 182,855,000	$ 89,280,000	245,400,000	122,723,000	102,499,000
Operating Segments
Segment Reporting Information [Line Items]
Operating income													128,376,000	573,433,000	315,154,000
Corporate And Reconciling Items
Segment Reporting Information [Line Items]
Services and fees													13,797,000	0	0
Total revenues														0	0
Corporate and other expenses													(72,725,000)	(58,905,000)	(38,893,000)
Capital Markets Segment
Segment Reporting Information [Line Items]
Total revenues													327,596,000	891,230,000	477,086,000
Capital Markets Segment | Operating Segments
Segment Reporting Information [Line Items]
Services and fees													292,933,000	555,585,000	318,714,000
Trading (loss) income and fair value adjustments on loans													(206,150,000)	212,922,000	55,873,000
Interest Income - Loan													240,813,000	122,723,000	102,499,000
Total revenues													327,596,000	891,230,000	477,086,000
Selling, general and administrative expenses													(171,006,000)	(345,455,000)	(198,962,000)
Restructuring charge													0	0	(917,000)
Interest expense - Securities lending and loan participations sold													(66,495,000)	(52,631,000)	(42,451,000)
Depreciation and amortization													(8,493,000)	(2,136,000)	(2,386,000)
Operating income													81,602,000	491,008,000	232,370,000
Wealth Management Segment
Segment Reporting Information [Line Items]
Total revenues													234,257,000	381,984,000	73,149,000
Wealth Management Segment | Operating Segments
Segment Reporting Information [Line Items]
Services and fees													230,735,000	374,361,000	72,345,000
Trading (loss) income and fair value adjustments on loans													3,522,000	7,623,000	804,000
Total revenues													234,257,000	381,984,000	73,149,000
Selling, general and administrative expenses													(258,134,000)	(357,130,000)	(68,368,000)
Restructuring charge													(4,955,000)	0	0
Depreciation and amortization													(5,488,000)	(8,920,000)	(1,880,000)
Operating income													(34,320,000)	15,934,000	2,901,000
Auction and Liquidation segment:
Segment Reporting Information [Line Items]
Total revenues													74,096,000	73,517,000	88,764,000
Auction and Liquidation segment: | Operating Segments
Segment Reporting Information [Line Items]
Services and fees													12,581,000	20,169,000	63,101,000
Revenues - Sale of goods													56,928,000	53,348,000	25,663,000
Direct cost of services													(23,920,000)	(30,719,000)	(40,730,000)
Cost of goods sold													(17,893,000)	(20,675,000)	(9,766,000)
Interest Income - Loan													4,587,000	0	0
Total revenues													74,096,000	73,517,000	88,764,000
Selling, general and administrative expenses													(19,683,000)	(14,069,000)	(12,357,000)
Restructuring charge													0	0	(140,000)
Depreciation and amortization													0	0	(2,000)
Operating income													12,600,000	8,054,000	25,769,000
Financial Consulting Segment
Segment Reporting Information [Line Items]
Total revenues													98,508,000	94,312,000	91,622,000
Financial Consulting Segment | Operating Segments
Segment Reporting Information [Line Items]
Services and fees													98,508,000	94,312,000	91,622,000
Selling, general and administrative expenses													(81,891,000)	(77,062,000)	(68,232,000)
Restructuring charge													0	0	500,000
Depreciation and amortization													(305,000)	(356,000)	(347,000)
Operating income													16,312,000	16,894,000	22,543,000
Communications Segment
Segment Reporting Information [Line Items]
Total revenues													235,655,000	93,347,000	87,138,000
Communications Segment | Operating Segments
Segment Reporting Information [Line Items]
Services and fees													228,129,000	88,490,000	83,666,000
Revenues - Sale of goods													7,526,000	4,857,000	3,472,000
Direct cost of services													(108,686,000)	(23,671,000)	(19,721,000)
Cost of goods sold													(8,592,000)	(6,278,000)	(2,694,000)
Total revenues													235,655,000	93,347,000	87,138,000
Selling, general and administrative expenses													(64,836,000)	(25,493,000)	(20,352,000)
Restructuring charge													(4,056,000)	0	0
Depreciation and amortization													(19,165,000)	(10,747,000)	(11,011,000)
Operating income													30,320,000	27,158,000	33,360,000
Consumer Segment
Segment Reporting Information [Line Items]
Total revenues													96,761,000	20,308,000	16,458,000
Consumer Segment | Operating Segments
Segment Reporting Information [Line Items]
Services and fees													18,940,000	20,308,000	16,458,000
Revenues - Sale of goods													77,821,000	0	0
Cost of goods sold													(52,162,000)	0	0
Total revenues													96,761,000	20,308,000	16,458,000
Selling, general and administrative expenses													(18,458,000)	(3,178,000)	(2,889,000)
Depreciation and amortization													(4,279,000)	(2,745,000)	(2,858,000)
Impairment of tradenames													0	0	(12,500,000)
Operating income													21,862,000	$ 14,385,000	$ (1,789,000)
All Other:
Segment Reporting Information [Line Items]
Total revenues													$ 13,797,000