EARNINGS PER SHARE - Schedule of basic and diluted earnings per share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								6 Months Ended		9 Months Ended		12 Months Ended
	Dec. 31, 2022	Sep. 30, 2022	Jun. 30, 2022	Mar. 31, 2022	Dec. 31, 2021	Sep. 30, 2021	Jun. 30, 2021	Mar. 31, 2021	Jun. 30, 2022	Jun. 30, 2021	Sep. 30, 2022	Sep. 30, 2021	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Earnings Per Share [Abstract]
Net (loss) income attributable to B. Riley Financial, Inc.	$ (57,445)	$ 47,837	$ (140,159)	$ (10,062)	$ 64,172	$ 50,550	$ 75,676	$ 254,656	$ (150,221)	$ 330,332	$ (102,384)	$ 380,882	$ (159,829)	$ 445,054	$ 205,148
Preferred stock dividends	(2,002)	(2,002)	(2,002)	(2,002)	(1,990)	(1,929)	(1,789)	(1,749)	(4,004)	(3,538)	(6,006)	(5,467)	(8,008)	(7,457)	(4,710)
Net (loss) income available to common shareholders	(59,447)	45,835	(142,161)	(12,064)	62,182	48,621	73,887	252,907	(154,225)	326,794	(108,390)	375,415	(167,837)	437,597	200,438
Net (loss) income applicable to common shareholders	$ (59,447)	$ 45,835	$ (142,161)	$ (12,064)	$ 62,182	$ 48,621	$ 73,887	$ 252,907	$ (154,225)	$ 326,794	$ (108,390)	$ 375,415	$ (167,837)	$ 437,597	$ 200,438
Weighted average common shares outstanding:
Basic	28,545,714	28,293,064	28,051,570	27,855,033	27,569,188	27,570,716	27,344,184	26,972,275	27,953,845	27,159,257	28,068,160	27,297,917	28,188,530	27,366,292	25,607,278
Effect of dilutive potential common shares:
Restricted stock units and warrants (in shares)													0	1,514,728	901,119
Contingently issuable shares (in shares)													0	124,582	0
Weighted average diluted common shares outstanding (in shares)	28,545,714	29,968,417	28,051,570	27,855,033	29,840,704	28,794,066	28,668,465	28,710,368	27,953,845	28,690,444	28,068,160	28,726,492	28,188,530	29,005,602	26,508,397
Basic income per common share (in dollars per share)	$ (2.08)	$ 1.62	$ (5.07)	$ (0.43)	$ 2.26	$ 1.76	$ 2.70	$ 9.38	$ (5.52)	$ 12.03	$ (3.86)	$ 13.75	$ (5.95)	$ 15.99	$ 7.83
Diluted income per common share (in dollars per share)	$ (2.08)	$ 1.53	$ (5.07)	$ (0.43)	$ 2.08	$ 1.69	$ 2.58	$ 8.81	$ (5.52)	$ 11.39	$ (3.86)	$ 13.07	$ (5.95)	$ 15.09	$ 7.56