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
 6 Months Ended 9 Months Ended
Jun. 30, 2018
Sep. 30, 2018
Dec. 31, 2017
Sep. 30, 2017
Property, Plant and Equipment [Line Items]        
Total property and equipment $ 3,494     $ 2,872
Less: accumulated depreciation (962)     (475)
Property and equipment, net 2,532 $ 14,642 $ 9,513 2,397
Fortress Biotech Inc [Member]        
Property, Plant and Equipment [Line Items]        
Total property and equipment   14,173 8,287  
Less: accumulated depreciation   (2,063) (1,171)  
Property and equipment, net   12,110 7,116  
Computer equipment [Member] | Fortress Biotech Inc [Member]        
Property, Plant and Equipment [Line Items]        
Total property and equipment   $ 648 543  
Estimated Useful Lives (in years)   3 years    
Furniture and fixtures [Member]        
Property, Plant and Equipment [Line Items]        
Total property and equipment $ 323     284
Estimated Useful Lives (in years) 5 years      
Furniture and fixtures [Member] | Fortress Biotech Inc [Member]        
Property, Plant and Equipment [Line Items]        
Total property and equipment   $ 1,128 1,009  
Estimated Useful Lives (in years)   5 years    
Machinery and equipment [Member] | Fortress Biotech Inc [Member]        
Property, Plant and Equipment [Line Items]        
Total property and equipment   $ 3,128 143  
Estimated Useful Lives (in years)   5 years    
Leasehold improvements [Member]        
Property, Plant and Equipment [Line Items]        
Total property and equipment $ 1,041     $ 1,006
Leasehold improvements [Member] | Fortress Biotech Inc [Member]        
Property, Plant and Equipment [Line Items]        
Total property and equipment   $ 9,236 5,351  
Leasehold improvements [Member] | Fortress Biotech Inc [Member] | Maximum [Member]        
Property, Plant and Equipment [Line Items]        
Estimated Useful Lives (in years)   15 years    
Leasehold improvements [Member] | Fortress Biotech Inc [Member] | Minimum [Member]        
Property, Plant and Equipment [Line Items]        
Estimated Useful Lives (in years)   5 years    
Construction in process [Member] | Fortress Biotech Inc [Member]        
Property, Plant and Equipment [Line Items]        
Total property and equipment [1]   $ 33 $ 1,241  
[1] Relates to the Mustang cell processing facility.