Fortress Biotech, Inc. Quarterly report pursuant to Section 13 or 15(d)

Sponsored Research and Clinical Trial Agreements - summary of Mustang expense related to its sponsored research agreements (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Research and Development in Process	$ 450	$ 97
Mustang Therapeutics, Inc [Member]
Research and Development in Process	450	75
Mustang Therapeutics, Inc [Member] \| COH – manufacturing [Member]
Research and Development in Process	0	75
Research and clinical trial agreements [Member] \| Mustang Therapeutics, Inc [Member]
Research and Development in Process	1,595	1,390
Research and clinical trial agreements [Member] \| Mustang Therapeutics, Inc [Member] \| City of Hope (COH) [Member]
Research and Development in Process	500	500
Research and clinical trial agreements [Member] \| Mustang Therapeutics, Inc [Member] \| COH – CD123 (MB-102) [Member]
Research and Development in Process	303	150
Research and clinical trial agreements [Member] \| Mustang Therapeutics, Inc [Member] \| COH – IL13Ra2 (MB-101) [Member]
Research and Development in Process	342	360
Research and clinical trial agreements [Member] \| Mustang Therapeutics, Inc [Member] \| COH – manufacturing [Member]
Research and Development in Process	114	114
Research and clinical trial agreements [Member] \| Mustang Therapeutics, Inc [Member] \| Fred HutchCD20 MB106 [Member]
Research and Development in Process	267	266
Research and clinical trial agreements [Member] \| Mustang Therapeutics, Inc [Member] \| BIDMC – CRISPR [Member]
Research and Development in Process	$ 69	$ 0