EARNINGS PER SHARE - Schedule of basic and diluted earnings per share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021
Earnings Per Share [Abstract]
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
Weighted average common shares outstanding:
Basic (in shares)	28,051,570	27,344,184	27,953,845	27,159,257
Effect of dilutive potential common shares:
Restricted stock units and warrants (in shares)	0	1,324,281	0	1,531,187
Diluted (in shares)	28,051,570	28,668,465	27,953,845	28,690,444
Basic (loss) income per common share (in dollars per share)	$ (5.07)	$ 2.70	$ (5.52)	$ 12.03
Diluted (loss) income per common share (in dollars per share)	$ (5.07)	$ 2.58	$ (5.52)	$ 11.39