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

Annual report pursuant to Section 13 and 15(d)

Commitments and Contingencies - Additional Information (Detail)

Commitments and Contingencies - Additional Information (Detail) € in Millions				1 Months Ended								12 Months Ended
	Jul. 12, 2018 USD ($)	Sep. 14, 2016 USD ($)	Oct. 03, 2014 USD ($)	Aug. 31, 2018 USD ($) ft²	Nov. 30, 2017 USD ($)	Nov. 30, 2017 USD ($)	Oct. 31, 2017 USD ($)	Oct. 27, 2017 USD ($) ft²	Jun. 30, 2017 USD ($) ft²	Oct. 31, 2015 USD ($) ft²	Oct. 30, 2015	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2012 USD ($) ft²	Dec. 31, 2019 USD ($)	Dec. 31, 2018 EUR (€)	Dec. 31, 2017 EUR (€)	Mar. 20, 2012 EUR (€)
Operating Leased Assets [Line Items]
Land Subject to Ground Leases \| ft²				3,681					2,295	6,100				8,700
Operating Leases, Rent Expense			$ 2,500,000						$ 55,000	$ 200,000				$ 100,000
Operating Leases, Rent Expense, Net												$ 1,700,000	$ 1,200,000
Lease Expiration Period											5 years
Lease Expiration Date												Nov. 30, 2020
Loss Contingency, Damages Sought, Value	$ 3,300,000
Accounts Payable and Accrued Liabilities, Current												$ 34,067,000	27,412,000
Legal Fees		$ 25,000,000
Administration Fee Payable												39,500
Operating Leases, Rent Expense, Minimum Rentals				$ 94,000
Scenario, Forecast [Member]
Operating Leased Assets [Line Items]
Accounts Payable and Accrued Liabilities, Current															$ 300,000
Letter of Credit [Member]
Operating Leased Assets [Line Items]
Increase (Decrease) in Security Deposits								$ 1,000,000
General and Administrative Expense [Member]
Operating Leased Assets [Line Items]
Legal Fees						$ 2,200,000
New York, NY office space [Member]
Operating Leased Assets [Line Items]
Lease Expiration Period			15 years
Waltham office space [Member]
Operating Leased Assets [Line Items]
Operating Leases, Rent Expense												$ 200,000	200,000
Opus Point Partners Management, LLC [Member]
Operating Leased Assets [Line Items]
Operating Leases, Rent Expense			$ 300,000
Percentage of Rentable Area			10.00%									9.00%
Prepaid Rent												$ 900,000	1,000,000
TG Therapeutics, Inc [Member]
Operating Leased Assets [Line Items]
Operating Leases, Rent Expense			$ 1,100,000
Percentage of Rentable Area			45.00%									46.00%
Journey Medical Corporation [Member]
Operating Leased Assets [Line Items]
Operating Leases, Rent Expense, Net												$ 100,000	100,000
Mustang [Member]
Operating Leased Assets [Line Items]
Land Subject to Ground Leases \| ft²								27,043
Operating Leases, Rent Expense								$ 600,000
Operating Leases, Rent Expense, Net												400,000	100,000
Payments for Legal Settlements					$ 200,000	200,000
Operating Leases, Rent Expense, Sublease Rentals								3,600,000
Land Improvements								3,500,000
Security Deposit								800,000
Increase (Decrease) in Security Deposits								1,300,000
Litigation Settlement, Expense						$ 2,000,000
Mustang [Member] \| Cash [Member]
Operating Leased Assets [Line Items]
Security Deposit								300,000
Increase (Decrease) in Security Deposits							$ 300,000
Mustang [Member] \| Letter of Credit [Member]
Operating Leased Assets [Line Items]
Increase (Decrease) in Security Deposits								$ 500,000
Dr.Falk Pharma [Member]
Operating Leased Assets [Line Items]
Contractual Obligation \| €																		€ 2.5
Accounts Payable and Accrued Liabilities, Current												$ 300,000	$ 3,000,000			€ 2.5	€ 2.5