Acquisitions (Details 4) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Weighted average basic shares outstanding	26,547,023	26,556,223	26,278,352	26,217,215	26,177,560	25,968,997	25,424,178	26,219,277	26,401,036	25,937,305	23,181,388
Weighted average diluted shares outstanding	28,412,871	28,233,423	26,896,573	26,687,531	26,177,560	26,854,261	26,397,513	27,271,819	27,529,157	26,764,856	24,290,904
MagicJack VocalTec [Member]
Revenues										$ 489,556
Net income attributable to B. Riley Financial, Inc.										$ 20,822
Basic earnings per share										$ 0.80
Diluted earnings per share										$ 0.78
Weighted average basic shares outstanding									26,401,036	25,937,305
Weighted average diluted shares outstanding									27,529,157	26,764,856