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

Sponsored Research and Clinical Trial Agreements (Narrative) (Details)

Sponsored Research and Clinical Trial Agreements (Narrative) (Details)			1 Months Ended				3 Months Ended
	Jul. 01, 2020 USD ($)	Feb. 17, 2017 USD ($)	Oct. 31, 2020 USD ($)	Jun. 30, 2020 USD ($)	May 31, 2020 USD ($)	Mar. 31, 2015 USD ($) installment	Mar. 31, 2021 USD ($)	Mar. 31, 2020 USD ($)	Sep. 30, 2020 USD ($)	Jul. 03, 2017 USD ($)
Research and development expense							$ 20,154,000	$ 15,117,000
Research and Clinical Trial Agreements [Member] \| City of Hope (COH) [Member] \| MB-102 (CD 123 CAR T for AML) [Member]
Sponsored research agreement, additional funding commitment		$ 100,000
Research and development expense							200,000	200,000
Upfront fees payment		$ 20,000
Funding commitment period		3 years
Research and Clinical Trial Agreements [Member] \| City of Hope (COH) [Member] \| MB-102 (CD 123 CAR T for AML) [Member] \| Completion of Clinical Development Milestones [Member]
Sponsored research agreement, additional funding commitment		$ 200,000
Research and Clinical Trial Agreements [Member] \| Aevitas [Member]
Research and development expense							248,000	281,000
Research and Clinical Trial Agreements [Member] \| Aevitas [Member] \| University of Massachusetts [Member]
Research and development expense							248,000	0
Research and Clinical Trial Agreements [Member] \| Aevitas [Member] \| University of Pennsylvania [Member]
Research and development expense							0	281,000
Research and Clinical Trial Agreements [Member] \| Mustang [Member]
Research and development expense							1,842,000	1,349,000
Research and Clinical Trial Agreements [Member] \| Mustang [Member] \| City of Hope (COH) [Member]
Research and development expense							0	500,000
Research and Clinical Trial Agreements [Member] \| Mustang [Member] \| City of Hope (COH) [Member] \| MB-102 (CD 123 CAR T for AML) [Member]
Research and development expense							205,000	230,000
Research and Clinical Trial Agreements [Member] \| Mustang [Member] \| City of Hope (COH) [Member] \| MB-104 (CS1 CAR T) [Member]
Research and development expense							175,000	0
Upfront fees payment				$ 800,000
Research and Clinical Trial Agreements [Member] \| Mustang [Member] \| City of Hope (COH) [Member] \| MB-101 (IL13R2 CAR T for Glioblastoma) [Member]
Sponsored research agreement, funding commitment						$ 2,000,000.0
Sponsored research agreement, additional funding commitment		100,000	$ 100,000
Research and development expense							514,000	92,000
Upfront fees payment		$ 9,300	29,000
Funding commitment period		3 years
Number of installments to pay the upfront fees \| installment						4
Research and Clinical Trial Agreements [Member] \| Mustang [Member] \| City of Hope (COH) [Member] \| MB-101 (IL13R2 CAR T for Glioblastoma) [Member] \| Completion of Clinical Development Milestones [Member]
Sponsored research agreement, additional funding commitment		$ 200,000
Payments of milestones			200,000
Research and Clinical Trial Agreements [Member] \| Mustang [Member] \| City of Hope (COH) [Member] \| MB-103 (HER2 CAR T) [Member]
Sponsored research agreement, funding commitment									$ 29,000
Research and development expense							123,000	0
Research and Clinical Trial Agreements [Member] \| Mustang [Member] \| City of Hope (COH) [Member] \| MB-105 (PSCA CAR T) [Member]
Research and development expense							50,000	0
Research and Clinical Trial Agreements [Member] \| Mustang [Member] \| City of Hope (COH) [Member] \| MB-105 (PSCA CAR T) [Member] \| Upon Execution of Agreements [Member]
Payments of milestones			33,000
Research and Clinical Trial Agreements [Member] \| Mustang [Member] \| Fred Hutchinson Cancer Research Center [Member] \| MB-106 (CD20 CAR T) [Member]
Sponsored research agreement, additional funding commitment										$ 800,000
Research and development expense							671,000	527,000
Research and Clinical Trial Agreements [Member] \| Mustang [Member] \| St. Jude Children's Research Hospital [Member] \| MB-107 (XSCID) [Member]
Research and development expense							104,000	0
Upfront fees payment	$ 1,100,000
Research and Clinical Trial Agreements [Member] \| Mustang [Member] \| Maximum [Member] \| City of Hope (COH) [Member] \| MB-104 (CS1 CAR T) [Member]
Sponsored research agreement, additional funding commitment				$ 2,400,000
Research and Clinical Trial Agreements [Member] \| Mustang [Member] \| Maximum [Member] \| City of Hope (COH) [Member] \| MB-103 (HER2 CAR T) [Member]
Sponsored research agreement, additional funding commitment									$ 3,000,000.0
Research and Clinical Trial Agreements [Member] \| Mustang [Member] \| Maximum [Member] \| City of Hope (COH) [Member] \| MB-105 (PSCA CAR T) [Member]
Payments of milestones			$ 2,300,000
Research and Clinical Trial Agreements [Member] \| Mustang [Member] \| Maximum [Member] \| Fred Hutchinson Cancer Research Center [Member] \| MB-106 (CD20 CAR T) [Member]
Sponsored research agreement, funding commitment										$ 5,300,000
Research and Clinical Trial Agreements [Member] \| Oncogenuity [Member]
Research and development expense							323,000	0
Research and Clinical Trial Agreements [Member] \| Oncogenuity [Member] \| Columbia University [Member]
Research and development expense							188,000	0
Funding commitment period					5 years
Research and Clinical Trial Agreements [Member] \| Oncogenuity [Member] \| University of California [Member]
Research and development expense							56,000	0
Research and Clinical Trial Agreements [Member] \| Oncogenuity [Member] \| University of Oxford [Member]
Research and development expense							$ 79,000	$ 0
Research and Clinical Trial Agreements [Member] \| Oncogenuity [Member] \| Maximum [Member] \| Columbia University [Member]
Sponsored research agreement, funding commitment					$ 4,800,000