Earnings Per Share (Details) - Schedule of basic and diluted earnings per share - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Schedule of basic and diluted earnings per share [Abstract]
Net income attributable to B. Riley Financial, Inc. (in Dollars)	$ 48,379	$ 34,302	$ 33,554	$ 64,482
Preferred stock dividends (in Dollars)	1,088		3,230
Net income applicable to common shareholders (in Dollars)	$ 47,291	$ 34,302	$ 30,324	$ 64,482
Weighted average common shares outstanding:
Basic	25,446,292	26,556,223	25,699,735	26,351,839
Effect of dilutive potential common shares:
Restricted stock units and warrants	1,604,156	1,613,993	989,965	836,791
Contingently issuable shares		63,207		63,207
Diluted	27,050,448	28,233,423	26,689,700	27,251,837
Basic income per common share (in Dollars per share)	$ 1.86	$ 1.29	$ 1.18	$ 2.45
Diluted income per common share (in Dollars per share)	$ 1.75	$ 1.21	$ 1.14	$ 2.37