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

Licenses Acquired - Summary Of Research and Development Arrangement Contract (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Research and Development Total	$ 6,090	$ 4,050
Aevitas [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Research and Development Total	0	1
Avenue [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Research and Development Total	1,000	0
Baergic[Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Research and Development Total	3,290	0
Caelum [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Research and Development Total	0	252
Checkpoint [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Research and Development Total	0	1,000
Cellvation [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Research and Development Total	0	1
Helocyte [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Research and Development Total	450	1,521
Mustang [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Research and Development Total	$ 1,350	$ 1,275