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

Sponsored Research and Clinical Trial Agreements - summary of Mustang's expense related to its sponsored research agreements (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Research and Development in Process		$ 0
Mustang Therapeutics Inc [Member]
Research and Development in Process	$ 1,407	1,424	$ 4,087	$ 4,029
COH CAR T [Member] \| Mustang Therapeutics Inc [Member]
Research and Development in Process	500	500	1,500	1,500
COH - CD123 [Member] \| Mustang Therapeutics Inc [Member]
Research and Development in Process	123	642	387	1,237
COH - IL13Ra2 [Member] \| Mustang Therapeutics Inc [Member]
Research and Development in Process	346	194	849	1,204
City of Hope - Manufacturing [Member] \| Mustang Therapeutics Inc [Member]
Research and Development in Process	114	0	344	0
Fred Hutch - CD20 [Member] \| Mustang Therapeutics Inc [Member]
Research and Development in Process	255	88	938	88
BIDMC CRISPR [Member] \| Mustang Therapeutics Inc [Member]
Research and Development in Process	$ 69	$ 0	$ 69	$ 0