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

Licenses Acquired (Narrative) (Details)

Licenses Acquired (Narrative) (Details) - USD ($) $ in Millions				9 Months Ended
	Sep. 29, 2021	Jun. 29, 2021	Apr. 01, 2021	Sep. 30, 2021	Dec. 31, 2020
Journey [Member] \| Contingent Payment Warrant [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Warrants, fair value				$ 3.8	$ 0.0
Journey [Member] \| Licensing Agreements [Member] \| Dr. Reddy's Laboratories, Ltd [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Upfront fees payment		$ 10.0
Payments of milestones		2.0
Maintenance fees		24.0
Journey [Member] \| Licensing Agreements [Member] \| Dr. Reddy's Laboratories, Ltd [Member] \| Achievement of Certain Clinical Development, Regulatory and First Commercial Sale milestones [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Payments of milestones		$ 163.0
Journey [Member] \| Licensing Agreements [Member] \| Dr. Reddy's Laboratories, Ltd [Member] \| Payable 90 days Following the Effective Date [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Payments of milestones	$ 8.0
Journey [Member] \| Licensing Agreements [Member] \| Minimum [Member] \| Dr. Reddy's Laboratories, Ltd [Member] \| Payable on Net Sales of the DFD-29 Product [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Sales royalties (as a percent)		10.00%
Journey [Member] \| Licensing Agreements [Member] \| Maximum [Member] \| Dr. Reddy's Laboratories, Ltd [Member] \| Payable on Net Sales of the DFD-29 Product [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Sales royalties (as a percent)		15.00%
Mustang [Member] \| Licensing Agreements [Member] \| Mayo Clinic [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Upfront fees payment			$ 0.8	$ 0.8