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

Fair Value Measurements - Derivative Contingently Issuable Warrant liabilities (Detail)

Fair Value Measurements - Derivative Contingently Issuable Warrant liabilities (Detail) - USD ($) $ in Thousands	1 Months Ended	5 Months Ended	6 Months Ended
	Mar. 31, 2018	Mar. 15, 2018	Jun. 30, 2018	Mar. 31, 2018
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Payment of convertible notes			$ (4,076)
Reclassification of warrant to equity			(13,615)
National [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair value at the beginning of period:	$ 13,615	$ 5,597		$ 5,597
Trading revenue gain		8,018
Reclassification of warrant to equity	(13,615)
Fair value at end of period:	0	13,615		0
Helocyte [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair value at the beginning of period:			87
Change in fair value			(87)
Fair value at end of period:			0
Helocyte [Member] \| Convertible Debt [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair value at the beginning of period:			4,700
Payment of convertible notes			(4,076)
Change in fair value			(291)
Fair value at end of period:			333
National Warrant Liabilities [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair value at the beginning of period:		$ 202		202
Change in fair value				1,349
Fair value at end of period:	$ 1,551			$ 1,551
Caelum Convertible Notes [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair value at the beginning of period:			10,059
Change in fair value			181
Fair value at end of period:			$ 10,240