SELECTED QUARTERLY FINANCIAL DATA (UNAUDITED) (Details) - USD ($)
$ / shares in Units, $ in Thousands
3 Months Ended 12 Months Ended
Dec. 31, 2016
Sep. 30, 2016
Jun. 30, 2016
Mar. 31, 2016
Dec. 31, 2015
Sep. 30, 2015
Jun. 30, 2015
Mar. 31, 2015
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Quarterly Financial Information Disclosure [Abstract]                      
Total revenues $ 93,178 $ 56,966 $ 20,261 $ 19,946 $ 19,761 $ 21,272 $ 45,461 $ 26,031      
Operating income (loss) 31,458 15,422 180 1,665 (1,326) 3,277 14,669 5,462 $ 48,725 $ 22,082 $ (7,431)
Income (loss) before income taxes 31,146 14,457 (92) 1,536 (1,418) 3,218 14,254 5,211      
(Provision) benefit for income taxes (8,137) (6,083) 65 (166) 372 (600) (5,684) (1,775) 14,321 7,688 (2,886)
Net income (loss) attributable to B. Riley 23,009 8,374 (27) 1,370 (1,046) 2,618 8,569 3,436 32,726 13,577 (5,795)
Net income (loss) attributable to B. Riley Financial, Inc. $ 12,440 $ 8,939 $ (101) $ 248 $ (1,004) $ 1,463 $ 8,664 $ 2,682 $ 21,526 $ 11,805 $ (5,801)
Earnings (loss) per share:                      
Basic $ 0.65 $ 0.47 $ (0.01) $ 0.02 $ (0.06) $ 0.09 $ 0.53 $ 0.17 $ 1.19 $ 0.73 $ (0.60)
Diluted $ 0.64 $ 0.47 $ (0.01) $ 0.01 $ (0.06) $ 0.09 $ 0.53 $ 0.17 $ 1.17 $ 0.73 $ (0.60)
Weighted average shares outstanding:                      
Basic 19,004,548 18,977,072 17,935,254 16,490,178 16,283,677 16,243,425 16,237,860 16,117,422 18,106,621 16,221,040 9,612,154
Diluted 19,511,292 19,208,527 17,935,254 16,553,953 16,283,677 16,344,649 16,310,829 16,162,304 18,391,852 16,265,915 9,612,154