Fortress Biotech, Inc. Annual report pursuant to Section 13 and 15(d)

Milestones and Sponsored Research Agreements - summary of Mustang's expense related to its sponsored research agreements (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Research and Development in Process	$ 4,050	$ 4,164
Mustang Therapeutics, Inc [Member]
Research and Development in Process	1,275	2,875
Mustang Therapeutics, Inc [Member] \| Research and clinical trial agreements [Member]
Research and Development in Process	5,719	5,504
Mustang Therapeutics, Inc [Member] \| City of Hope [Member] \| Research and clinical trial agreements [Member]
Research and Development in Process	2,000	2,000
Mustang Therapeutics, Inc [Member] \| City of Hope - CD123 [Member] \| Research and clinical trial agreements [Member]
Research and Development in Process	835	1,367
Mustang Therapeutics, Inc [Member] \| COH - IL13Ra2 [Member] \| Research and clinical trial agreements [Member]
Research and Development in Process	1,056	1,385
Mustang Therapeutics, Inc [Member] \| City of Hope - Manufacturing [Member] \| Research and clinical trial agreements [Member]
Research and Development in Process	458	0
Mustang Therapeutics, Inc [Member] \| Fred Hutch - CD20 [Member] \| Research and clinical trial agreements [Member]
Research and Development in Process	1,301	614
Mustang Therapeutics, Inc [Member] \| BIDMC CRISPR [Member] \| Research and clinical trial agreements [Member]
Research and Development in Process	$ 69	$ 138