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

Segment Information - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016
Customer One [Member]
Segment Reporting Information [Line Items]
Sales Revenue, Goods, Gross	$ 3.0	$ 0.2	$ 6.7	$ 0.8
Accounts Receivable, Net	1.7		1.7		$ 1.1
Customer Two [Member]
Segment Reporting Information [Line Items]
Sales Revenue, Goods, Gross	1.7	$ 43.0	6.0	0.3
Accounts Receivable, Net	$ 1.5		$ 1.5		$ 0.5
Customer Three [Member]
Segment Reporting Information [Line Items]
Sales Revenue, Goods, Gross				$ 0.3