EARNINGS PER SHARE - Schedule of basic and diluted earnings per share (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Earnings Per Share [Abstract]
Net (loss) income attributable to B. Riley Financial, Inc.	$ (99,910)	$ (159,829)	$ 445,054
Preferred stock dividends	(8,057)	(8,008)	(7,457)
Net (loss) income available to common shareholders	(107,967)	(167,837)	437,597
Net (loss) income applicable to common shareholders	$ (107,967)	$ (167,837)	$ 437,597
Weighted average common shares outstanding:
Basic	29,265,099	28,188,530	27,366,292
Effect of dilutive potential common shares:
Restricted stock units and warrants (in shares)	0	0	1,514,728
Contingently issuable shares (in shares)	0	0	124,582
Weighted average diluted common shares outstanding (in shares)	29,265,099	28,188,530	29,005,602
Basic (loss) income per common share (in dollars per share)	$ (3.69)	$ (5.95)	$ 15.99
Diluted (loss) income per common share (in dollars per share)	$ (3.69)	$ (5.95)	$ 15.09