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

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

Sponsored Research and Clinical Trial Agreements (Narrative) (Details) £ in Millions										1 Months Ended				12 Months Ended
	Dec. 16, 2020 USD ($)	Jul. 24, 2018 USD ($)	Mar. 17, 2018 USD ($)	Jan. 25, 2018 USD ($)	Jan. 03, 2018 USD ($)	Nov. 30, 2017 USD ($)	Nov. 28, 2017 USD ($)	Feb. 17, 2017 USD ($)	Mar. 31, 2015 USD ($) installment	Jan. 31, 2021 USD ($)	Jan. 31, 2021 GBP (£)	Oct. 31, 2020 USD ($)	Jun. 30, 2020 USD ($)	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Dec. 16, 2020 GBP (£)	Nov. 30, 2020 USD ($)	Sep. 30, 2020 USD ($)	May 31, 2020 USD ($)	Jul. 03, 2017 USD ($)	Oct. 31, 2016 USD ($)
Research and development expenses														$ 64,109,000	$ 81,326,000
Research and Clinical Trial Agreements [Member] \| Aevitas [Member] \| AAV Gene Therapies [Member]
Research and development expenses														948,000	1,133,000
Research and Clinical Trial Agreements [Member] \| Aevitas [Member] \| University of Massachusetts [Member]
Sponsored research agreement, funding commitment																			$ 700,000
Research and Clinical Trial Agreements [Member] \| Aevitas [Member] \| University of Massachusetts [Member] \| Within 30 days of Execution [Member]
Sponsored research agreement, funding commitment																			$ 400,000
Research and Clinical Trial Agreements [Member] \| Aevitas [Member] \| University of Massachusetts [Member] \| AAV Gene Therapies [Member]
Payments for research and development expenses				$ 800,000
Sponsored research agreement, funding commitment				$ 800,000
Research and development expenses														381,000	0
Research and Clinical Trial Agreements [Member] \| Aevitas [Member] \| University of Pennsylvania [Member] \| AAV Gene Therapies [Member]
Payments for research and development expenses		$ 300,000
Sponsored research agreement, funding commitment		$ 2,000,000.0
Research and development expenses														567,000	1,067,000
Research and Clinical Trial Agreements [Member] \| Aevitas [Member] \| Duke University School of Medicine [Member] \| AAV Gene Therapies [Member]
Research and development expenses														0	66,000
Research and Clinical Trial Agreements [Member] \| Cellvation [Member] \| University of Texas [Member]
Sponsored research agreement, funding commitment																					$ 800,000
Research and development expenses														0	100,000
Research and Clinical Trial Agreements [Member] \| Mustang [Member]
Research and development expenses														7,717,000	6,143,000
Research and Clinical Trial Agreements [Member] \| Mustang [Member] \| City of Hope (COH) [Member]
Sponsored research agreement, funding commitment									$ 2,000,000.0
Research and development expenses														500,000	2,000,000
Number of installments to pay the upfront fees \| installment									4
Research and Clinical Trial Agreements [Member] \| Mustang [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 expenses														433,000	1,202,000
Upfront fees payment								20,000
Research and Clinical Trial Agreements [Member] \| Mustang [Member] \| City of Hope (COH) [Member] \| MB-102 (CD 123 CAR T for AML) [Member] \| Over Three Years [Member]
Sponsored research agreement, additional funding commitment								200,000
Research and Clinical Trial Agreements [Member] \| Mustang [Member] \| City of Hope (COH) [Member] \| MB-104 (CS1 CAR T) [Member]
Research and development expenses														885,000	0
Research and Clinical Trial Agreements [Member] \| Mustang [Member] \| City of Hope (COH) [Member] \| MB-101 (IL13R2 CAR T for Glioblastoma) [Member]
Sponsored research agreement, additional funding commitment								100,000
Research and development expenses														530,000	876,000
Upfront fees payment								$ 9,300				$ 29,375
Payments of milestones												100,000
Funding commitment period								3 years
Research and Clinical Trial Agreements [Member] \| Mustang [Member] \| City of Hope (COH) [Member] \| MB-101 (IL13R2 CAR T for Glioblastoma) [Member] \| Over Three Years [Member]
Research and development expenses								$ 200,000
Research and Clinical Trial Agreements [Member] \| Mustang [Member] \| City of Hope (COH) [Member] \| MB-101 (IL13R2 CAR T for Glioblastoma) [Member] \| Clinical Development and Regulatory Milestones [Member]
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																		$ 29,375
Research and development expenses														1,519,000	0
Research and Clinical Trial Agreements [Member] \| Mustang [Member] \| City of Hope (COH) [Member] \| MB-105 (PSCA CAR T) [Member]
Sponsored research agreement, funding commitment												33,000
Research and development expenses														204,000	0
Research and Clinical Trial Agreements [Member] \| Mustang [Member] \| City of Hope (COH) [Member] \| Manufacturing License [Member]
Sponsored research agreement, funding commitment					$ 900,000
Research and development expenses														0	457,000
Funding commitment period					2 years
Research and Clinical Trial Agreements [Member] \| Mustang [Member] \| City of Hope (COH) [Member] \| MB-107 (XSCID) [Member]
Sponsored research agreement, funding commitment															800,000
Research and Clinical Trial Agreements [Member] \| Mustang [Member] \| Beth Israel Deaconess Medical Center Inc. [Member] \| CRISPR (multiple programs) [Member]
Research and development expenses														0	69,000
Research and Clinical Trial Agreements [Member] \| Mustang [Member] \| Beth Israel Deaconess Medical Center Inc. [Member] \| CRISPR (multiple programs) [Member] \| Over Three Years [Member]
Sponsored research agreement, funding commitment							$ 800,000
Funding commitment period							3 years
Research and Clinical Trial Agreements [Member] \| Mustang [Member] \| Fred Hutchinson Cancer Research Center [Member] \| Manufacturing License [Member]
Payments for research and development expenses			$ 600,000											0	200,000
Research and Clinical Trial Agreements [Member] \| Mustang [Member] \| Fred Hutchinson Cancer Research Center [Member] \| MB-106 (CD20 CAR T) [Member]
Research and development expenses														1,804,000	762,000
Research and Clinical Trial Agreements [Member] \| Mustang [Member] \| St. Jude Children's Research Hospital [Member] \| MB-107 (XSCID) [Member]
Research and development expenses														1,842,000	777,000
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, 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, 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]
Sponsored research agreement, funding commitment												$ 2,300,000
Research and Clinical Trial Agreements [Member] \| Oncogenuity [Member] \| Columbia University [Member]
Research and development expenses														$ 500,000	0
Funding commitment period														5 years
Research and Clinical Trial Agreements [Member] \| Oncogenuity [Member] \| University of Oxford [Member]
Funding commitment period	18 months
Research and Clinical Trial Agreements [Member] \| Oncogenuity [Member] \| University of Oxford [Member] \| Subsequent Events [Member]
Upfront fees payment										$ 100,000	£ 0.1
Research and Clinical Trial Agreements [Member] \| Oncogenuity [Member] \| Maximum [Member] \| Columbia University [Member]
Sponsored research agreement, funding commitment														$ 4,800,000
Research and Clinical Trial Agreements [Member] \| Oncogenuity [Member] \| Maximum [Member] \| University of Oxford [Member]
Sponsored research agreement, funding commitment	$ 600,000															£ 0.4
Research and Clinical Trial Agreements [Member] \| Tamid [Member] \| University of North Carolina [Member]
Research and development expenses														0	0
Upfront fees payment						$ 800,000
Research and Clinical Trial Agreements [Member] \| Tamid [Member] \| University of North Carolina [Member] \| Over Three Years [Member]
Sponsored research agreement, funding commitment						$ 2,300,000
Funding commitment period						3 years
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 expenses														$ 1,800,000	$ 600,000
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