EARNINGS PER SHARE - Schedule of basic and diluted earnings per share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021
Earnings Per Share [Abstract]
Net income (loss) attributable to B. Riley Financial, Inc.	$ 47,837	$ 50,550	$ (102,384)	$ 380,882
Preferred stock dividends	(2,002)	(1,929)	(6,006)	(5,467)
Net income (loss) available to common shareholders	45,835	48,621	(108,390)	375,415
Net income (loss) available to common shareholders	$ 45,835	$ 48,621	$ (108,390)	$ 375,415
Weighted average common shares outstanding:
Basic (in shares)	28,293,064	27,570,716	28,068,160	27,297,917
Effect of dilutive potential common shares:
Restricted stock units and warrants (in shares)	1,675,353	1,223,350	0	1,428,575
Diluted (in shares)	29,968,417	28,794,066	28,068,160	28,726,492
Basic (loss) income per common share (in dollars per share)	$ 1.62	$ 1.76	$ (3.86)	$ 13.75
Diluted (loss) income per common share (in dollars per share)	$ 1.53	$ 1.69	$ (3.86)	$ 13.07