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

Licenses Acquired - Additional Information (Detail) - USD ($)	1 Months Ended		3 Months Ended
	Jan. 31, 2018	Mar. 31, 2015	Mar. 31, 2018	Mar. 31, 2017	Feb. 02, 2018
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Research And Development In Process			$ 97,000	$ 1,294,000
Payments for Fees		$ 1,000,000
City Of Hope [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Payment of Upfront Fees	$ 75,000
Collaborative Agreements with TGTX [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Proceeds from Option Fee					$ 50,000
Collaborative Agreements with TGTX [Member] \| NeuPharma [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Payments for Fees			44,000	28,000
Caelum [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Research And Development In Process			0	200,000
Cyprium [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Research And Development In Process			$ 0	$ 100,000
Manufacturing Methods License [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Annual Maintenance Fee Payable	$ 15,000