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

Annual report pursuant to Section 13 and 15(d)

Milestones and Sponsored Research Agreements - Additional Information (Detail)

Milestones and Sponsored Research Agreements - Additional Information (Detail) - USD ($)					1 Months Ended							12 Months Ended
	Mar. 12, 2018	Jan. 03, 2018	Jul. 03, 2017	Mar. 05, 2015	Oct. 29, 2018	Nov. 30, 2017	Nov. 28, 2017	Jun. 30, 2017	Feb. 17, 2017	Mar. 31, 2016	Feb. 29, 2016	Dec. 31, 2018	Dec. 31, 2017	Oct. 31, 2016
Research and Development Expense												$ 83,333,000	$ 48,322,000
Payment of Upfront Fees												1,000,000
Payments to Acquire in Process Research and Development												1,074,000	3,365,000
Reimbursement Of Cost Recognized As Revenue												35,000	600,000
Revenue Recognition Milestone Method Payments Due					$ 2,000,000
Sponsor Research Agreement Funding Commitment		$ 900,000				$ 2,300,000
Research and Development Arrangement, Contract to Perform for Others, Costs Incurred, Gross	$ 100,000
Research and Development Arrangement, Contract to Perform for Others, Description and Terms		2 year
SPR Sponsored Research Agreement [Member]
Research and Development Expense												100,000	100,000
Revenue Recognition Milestone Method Payments Due Over Three Years							$ 800,000
Checkpoint Therapeutics, Inc [Member]
Stock Issued During Period, Value, Purchase of Assets												22,000,000
AR CD123 License [Member]
Revenue Recognition Milestone Method Payments Due Over Three Years									$ 200,000
UPenn Sponsored Research Agreement [Member]
Research and Development Expense												500,000
Payments For Research And Development Expenses												300,000
Sponsor Research Agreement Funding Commitment												2,000,000
Umass Sponsored Research Agreement [Member]
Research and Development Expense												800,000
Payments For Research And Development Expenses												800,000
Sponsor Research Agreement Funding Commitment												800,000
Pep Vax [Member]
Payments For Research And Development Expenses												100,000	1,100,000
Triplex [Member]
Payments For Research And Development Expenses													2,600,000
Helocyte Inc [Member]
Payments For Research And Development Expenses												100,000	3,700,000
Payment of Upfront								$ 1,500,000
Mustang Bio, Inc [Member]
Research And Development Expense Payable Milestone Payment									200,000
Research and Development Expense												1,300,000	600,000
Payment of Upfront Fees									9,300
Revenue Recognition Milestone Method Payments Due									100,000
Mustang Bio, Inc [Member] \| AR IL-13 License [Member]
Research and Development Expense												1,100,000	1,400,000
Mustang Bio, Inc [Member] \| CD20 Technology License [Member]
Payment of Upfront Fees			$ 5,300,000
UCLB [Member]
Payment of Upfront Fees												$ 100,000
UCLB [Member] \| Minimum [Member]
Royalty Percentage												3.00%
UCLB [Member] \| Maximum [Member]
Royalty Percentage												5.00%
Cellvation [Member]
Research And Development Expense Payable Milestone Payment														$ 800,000
Research and Development Expense												$ 300,000	100,000
City Of Hope [Member]
Research And Development Expense Payable Milestone Payment										$ 2,000,000	$ 3,400,000
Research and Development Expense												500,000	0
Payments to Acquire in Process Research and Development										$ 1,000,000	$ 1,000,000
City Of Hope [Member] \| AR CD123 License [Member]
Research and Development Expense												800,000	1,400,000
Payment of Upfront Fees									20,000
Revenue Recognition Milestone Method Payments Due									$ 100,000
Pentamer [Member]
Payments For Research And Development Expenses												1,300,000	200,000
Mustag [Member] \| COH [Member]
Research and Development Expense												2,000,000	2,000,000
Amount payable for research				$ 2,000,000
Tamid [Member]
Research and Development Expense												$ 700,000	$ 100,000
Research and development payments due						$ 800,000