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

Revenues from Contracts and Significant Customers (Narrative) (Details) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2021 USD ($)	Sep. 30, 2020 USD ($)	Sep. 30, 2021 USD ($) product	Sep. 30, 2020 USD ($)	Dec. 31, 2020 customer
Disaggregation of Revenue [Line Items]
Number of marketed products \| product			7
Revenue from Contract with Customer, Including Assessed Tax \| $	$ 19,610	$ 9,447	$ 45,617	$ 30,808
Dermatology Products Sales [Member] \| Customer Concentration Risk [Member] \| Accounts Receivable [Member]
Disaggregation of Revenue [Line Items]
Number of customers \| customer					1
Dermatology Products Sales [Member] \| One Customer [Member] \| Customer Concentration Risk [Member] \| Revenue [Member]
Disaggregation of Revenue [Line Items]
Concentration risk, percentage	10.10%
Dermatology Products Sales [Member] \| Customer one [Member] \| Customer Concentration Risk [Member] \| Accounts Receivable [Member]
Disaggregation of Revenue [Line Items]
Concentration risk, percentage			20.70%		14.50%
Dermatology Products Sales [Member] \| Customer Two [Member] \| Customer Concentration Risk [Member] \| Accounts Receivable [Member]
Disaggregation of Revenue [Line Items]
Concentration risk, percentage			14.90%