Quarterly report pursuant to Section 13 or 15(d)

Property and Equipment - Components of Property and Equipment (Detail)

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Property and Equipment - Components of Property and Equipment (Detail) - USD ($)
$ in Thousands
9 Months Ended
Sep. 30, 2017
Dec. 31, 2016
Property, Plant and Equipment [Line Items]    
Property and equipment, net $ 8,221 $ 7,376
Fortress Biotech Inc [Member]    
Property, Plant and Equipment [Line Items]    
Total property and equipment 7,015 6,657
Less: accumulated depreciation (986) (445)
Property and equipment, net 6,029 6,212
Computer Equipment [Member] | Fortress Biotech Inc [Member]    
Property, Plant and Equipment [Line Items]    
Total property and equipment $ 523 440
Useful Life (Years) 3 years  
Furniture and Fixtures [Member] | Fortress Biotech Inc [Member]    
Property, Plant and Equipment [Line Items]    
Total property and equipment $ 1,002 821
Useful Life (Years) 5 years  
Leasehold Improvements [Member] | Fortress Biotech Inc [Member]    
Property, Plant and Equipment [Line Items]    
Total property and equipment $ 5,351 5,396
Property, Plant and Equipment, Estimated Useful Lives Various  
Construction in progress [Member] | Fortress Biotech Inc [Member]    
Property, Plant and Equipment [Line Items]    
Total property and equipment [1] $ 139 $ 0
[1] In connection with Mustang’s manufacturing facility, Mustang incurred $0.1 million related to the design of the facility as of September 30, 2017.