Business Segments (Details) - Schedule of reportable segments - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Segment Reporting Information [Line Items]
Selling, general and administrative expenses	$ (97,143)	$ (101,092)	$ (291,449)	$ (287,963)
Restructuring (charge) recovery	(1,557)		(1,557)	(1,699)
Interest expense - Securities lending and loan participations sold	(10,975)	(10,273)	(30,669)	(22,579)
Depreciation and amortization			(14,765)	(14,217)
Segment income	83,501	59,851	93,697	129,084
Impairment of tradenames			12,500
Consolidated operating income from reportable segments	90,443	70,468	121,769	157,862
Income (loss) on equity investments			(145)	(4,049)
Interest expense	16,374	12,772	48,537	35,130
Provision for income taxes	18,711	14,409	13,380	26,802
Net income	48,892	34,144	32,172	64,432
Net income (loss) attributable to noncontrolling interests	513	(158)	(1,382)	(50)
Net income attributable to B. Riley Financial, Inc.			(1,005)	(1,454)
Preferred stock dividends	1,088		3,230
Net income available to common shareholders	47,291	34,302	30,324	64,482
Capital Markets Segment [Member]
Segment Reporting Information [Line Items]
Revenues - Services and fees	89,032	68,062	280,303	187,768
Trading income (losses) and fair value adjustments on loans	31,753	40,268	(36,142)	71,730
Interest income - Loans and securities lending	26,026	25,766	72,383	54,147
Total revenues	146,811	134,096	316,544	313,645
Selling, general and administrative expenses	(68,442)	(70,140)	(204,183)	(196,570)
Restructuring (charge) recovery	(1,417)		(1,417)	4
Interest expense - Securities lending and loan participations sold	(10,975)	(10,273)	(30,669)	(22,579)
Depreciation and amortization	(1,166)	(1,281)	(3,362)	(3,844)
Segment income	64,811	52,402	76,913	90,656
Auction and Liquidation segment [Member]
Segment Reporting Information [Line Items]
Revenues - Services and fees	21,473	11,232	49,340	65,681
Revenues - Sale of goods	22,712	54	23,757	1,230
Total revenues	44,185	11,286	73,097	66,911
Direct cost of services	(18,373)	(2,371)	(36,406)	(21,584)
Cost of goods sold	(9,046)	(126)	(9,360)	(992)
Selling, general and administrative expenses	(4,625)	(2,835)	(8,880)	(9,045)
Restructuring (charge) recovery	(140)		(140)
Depreciation and amortization	(1)	(1)	(2)	(5)
Segment income	12,000	5,953	18,309	35,285
Valuation and Appraisal segment [Member]
Segment Reporting Information [Line Items]
Revenues - Services and fees	9,655	10,818	26,112	29,143
Selling, general and administrative expenses	(6,632)	(7,331)	(19,643)	(21,492)
Depreciation and amortization	(51)	(36)	(139)	(100)
Segment income	2,972	3,451	6,330	7,551
Principal Investments - United Online and magicJack segment [Member]
Segment Reporting Information [Line Items]
Revenues - Services and fees	20,663	22,999	63,037	74,383
Revenues - Sale of goods	939	864	2,718	2,793
Total revenues	21,602	23,863	65,755	77,176
Direct cost of services	(4,891)	(5,565)	(14,795)	(20,131)
Cost of goods sold	(767)	(785)	(2,082)	(2,843)
Selling, general and administrative expenses	(4,840)	(5,895)	(14,352)	(18,410)
Restructuring (charge) recovery				(1,703)
Depreciation and amortization	(2,736)	(2,956)	(8,466)	(9,719)
Segment income	8,368	8,662	26,060	24,370
Brands Segment [Member]
Segment Reporting Information [Line Items]
Revenues - Services and fees	4,000		11,007
Selling, general and administrative expenses	(994)		(2,207)
Depreciation and amortization	(714)		(2,143)
Impairment of tradenames			(12,500)
Segment income (loss)	2,292		(5,843)
Consolidated operating (loss) income from reportable segments [Member]
Segment Reporting Information [Line Items]
Corporate and other expenses	(6,942)	(10,617)	(28,072)	(28,778)
Interest income	67	361	537	1,329
Income (loss) on equity investments	409	1,113	(145)	(4,049)
Interest expense	(16,374)	(12,772)	(48,537)	(35,130)
Income before income taxes	67,603	48,553	45,552	91,234
Provision for income taxes	(18,711)	(14,409)	(13,380)	(26,802)
Net income	48,892	34,144	32,172	64,432
Net income (loss) attributable to noncontrolling interests	513	(158)	(1,382)	(50)
Net income attributable to B. Riley Financial, Inc.	48,379	34,302	33,554	64,482
Preferred stock dividends	1,088		3,230
Net income available to common shareholders	$ 47,291	$ 34,302	$ 30,324	$ 64,482