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

Fair Value Measurements - Contingently Issuable Warrants with option pricing model (Detail)

Fair Value Measurements - Contingently Issuable Warrants with option pricing model (Detail)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Expected dividend yield		0.00%
Helocyte [Member] \| Measurement Input, Risk Free Interest Rate [Member] \| Minimum [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Risk-free interest rate		2.04%
Helocyte [Member] \| Measurement Input, Risk Free Interest Rate [Member] \| Maximum [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Risk-free interest rate		2.08%
Helocyte [Member] \| Measurement Input, Expected Dividend Rate [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Expected dividend yield		0.00%
Helocyte [Member] \| Measurement Input, Expected Term [Member] \| Minimum [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Expected term in years		3 years 6 months
Helocyte [Member] \| Measurement Input, Expected Term [Member] \| Maximum [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Expected term in years		3 years 11 months 1 day
Helocyte [Member] \| Measurement Input, Price Volatility [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Expected volatility		70.00%
Caelum [Member] \| Contingently Issuable Warrants [Member] \| Measurement Input, Risk Free Interest Rate [Member] \| Minimum [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Risk-free interest rate	2.905%	2.154%
Caelum [Member] \| Contingently Issuable Warrants [Member] \| Measurement Input, Risk Free Interest Rate [Member] \| Maximum [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Risk-free interest rate	2.909%	2.168%
Caelum [Member] \| Contingently Issuable Warrants [Member] \| Measurement Input, Expected Dividend Rate [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Expected dividend yield	8211.00%	8211.00%
Caelum [Member] \| Contingently Issuable Warrants [Member] \| Measurement Input, Expected Term [Member] \| Minimum [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Expected term in years	3 years 10 months 2 days	4 years 6 months 29 days
Caelum [Member] \| Contingently Issuable Warrants [Member] \| Measurement Input, Expected Term [Member] \| Maximum [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Expected term in years	3 years 11 months 16 days	4 years 8 months 16 days
Caelum [Member] \| Contingently Issuable Warrants [Member] \| Measurement Input, Price Volatility [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Expected volatility	70.00%	70.00%