EARNINGS PER SHARE - Schedule of basic and diluted earnings per share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Earnings Per Share [Abstract]
Net (loss) income attributable to B. Riley Financial, Inc.	$ (10,062)	$ 254,656
Preferred stock dividends	(2,002)	(1,749)
Net (loss) income available to common shareholders	(12,064)	252,907
Net (loss) income available to common shareholders	$ (12,064)	$ 252,907
Weighted average common shares outstanding:
Basic (in shares)	27,855,033	26,972,275
Effect of dilutive potential common shares:
Restricted stock units and warrants (in shares)	0	1,738,093
Diluted (in shares)	27,855,033	28,710,368
Basic (loss) income per common share (in dollars per share)	$ (0.43)	$ 9.38
Diluted (loss) income per common share (in dollars per share)	$ (0.43)	$ 8.81