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

Quarterly report pursuant to Section 13 or 15(d)

Debt and Interest- Additional Information (Detail)

Debt and Interest- Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands			1 Months Ended							3 Months Ended	9 Months Ended
	Jul. 05, 2017	May 01, 2017	Sep. 30, 2017	Aug. 31, 2017	Jul. 31, 2017	Jun. 30, 2017	May 31, 2017	Mar. 31, 2017	Mar. 17, 2017	Sep. 30, 2017	Sep. 30, 2017	Sep. 30, 2016	Jun. 26, 2017	Dec. 31, 2016	Feb. 13, 2014
Debt [Line Items]
Warrant exercise price													$ 4.02
Proceeds from Notes Payable											$ 0	$ 920
Notes Payable			$ 63,618							$ 63,618	63,618			$ 28,215
Proceeds From Convertible Debt											9,914	3,018
Payments of Financing Costs											$ 1,081	$ 0
Class of Warrant or Right, Exercise Price of Warrants or Rights													$ 4.02
Maximum [Member]
Debt [Line Items]
Warrant exercise price			$ 4.75							$ 4.75	$ 4.75
Class of Warrant or Right, Exercise Price of Warrants or Rights			$ 4.75							$ 4.75	$ 4.75
Israel Discount Bank Of New York [Member]
Debt [Line Items]
Debt Instrument, Face Amount															$ 15,000
Notes Payable			$ 14,900							$ 14,900	$ 14,900
Debt Instrument, Collateral Amount			15,000							15,000	15,000
Opus Credit Facility [Member]
Debt [Line Items]
Class Of Warrant Or Right Discount On Warrant			1,300							1,300	1,300
Warrants and Rights Outstanding			$ 9,500							$ 9,500	$ 9,500
NSC 2017 Note [Member]
Debt [Line Items]
Warrant exercise price								$ 3.70
Debt Instrument, Interest Rate, Stated Percentage								8.00%
Debt Instrument, Face Amount								$ 3,250
Debt Instrument, Maturity Date, Description											Each Note is due on the third anniversary of its issuance, provided that the Company may extend the maturity date for two one-year periods in its sole discretion
Paid-in-Kind Interest, Percentage								7.00%
Line of Credit Facility, Current Borrowing Capacity								$ 50,000
Percentage Of Placement Agent Fee									10.00%		10.00%
Warrant On Sale Price Of Note Percentage			10.00%						10.00%	10.00%	10.00%
Proceeds from Fees Received								$ 300
Class of Warrant or Right, Number of Securities Called by Warrants or Rights			716,180							716,180	716,180
Class of Warrant or Right, Exercise Price of Warrants or Rights								$ 3.70
NSC 2017 Note [Member] \| First Closing [Member]
Debt [Line Items]
Proceeds from Issuance of Debt								$ 3,200
NSC 2017 Note [Member] \| Secoud Closing [Member]
Debt [Line Items]
Warrant exercise price		$ 3.65
Proceeds from Notes Payable		$ 8,600
Proceeds from Fees Received		$ 900
Class of Warrant or Right, Number of Securities Called by Warrants or Rights		234,438	87,946							87,946	87,946
Class of Warrant or Right, Exercise Price of Warrants or Rights		$ 3.65
NSC 2017 Note [Member] \| Third Closing [Member]
Debt [Line Items]
Warrant exercise price							$ 3.61
Proceeds from Notes Payable							$ 5,300
Proceeds from Fees Received							$ 500
Class of Warrant or Right, Number of Securities Called by Warrants or Rights							147,806
Class of Warrant or Right, Exercise Price of Warrants or Rights							$ 3.61
NSC 2017 Note [Member] \| Fourth Closing [Member]
Debt [Line Items]
Warrant exercise price						$ 4.75
Proceeds from Notes Payable						$ 1,800
Proceeds from Fees Received						$ 200
Class of Warrant or Right, Number of Securities Called by Warrants or Rights						38,315
Class of Warrant or Right, Exercise Price of Warrants or Rights						$ 4.75
NSC 2017 Note [Member] \| Fifth Closing [Member]
Debt [Line Items]
Warrant exercise price				$ 4.75
Proceeds from Notes Payable				$ 3,000
Proceeds from Fees Received				$ 300
Class of Warrant or Right, Number of Securities Called by Warrants or Rights				63,526
Class of Warrant or Right, Exercise Price of Warrants or Rights				$ 4.75
NSC 2017 Note [Member] \| Sixth Closing [Member]
Debt [Line Items]
Warrant exercise price			$ 4.42							$ 4.42	$ 4.42
Proceeds from Notes Payable			$ 6,400
Proceeds from Fees Received			$ 600
Class of Warrant or Right, Number of Securities Called by Warrants or Rights			144,149							144,149	144,149
Class of Warrant or Right, Exercise Price of Warrants or Rights			$ 4.42							$ 4.42	$ 4.42
NSC 2017 Note [Member] \| Maximum [Member]
Debt [Line Items]
Debt Instrument, Face Amount								$ 40,000
Caelum Convertible Notes [Member]
Debt [Line Items]
Debt Instrument, Face Amount					$ 10,000
Debt Instrument Issuance, Percentage of Commission					10.00%
Proceeds From Convertible Debt					$ 9,900					$ 9,900
Payments of Financing Costs					$ 900					$ 900
Class of Warrant or Right, Percentage Securities Called by Warrants or Rights					10.00%					10.00%
Class of Warrant or Right, Exercise Price percentage					110.00%					110.00%
Class of Warrant or Right, Exercise Price Description											the exercise price will be $75 million dollars divided by the total number of fully-diluted shares of Common Stock outstanding immediately prior to exercise of the warrant, giving effect to the assumed conversion of all options, warrants, and convertible securities of the Company
Debt Conversion, Description											The notes convert upon a qualified financing in which Caelum raises gross proceeds of at least $10 million as follows: the lesser of (a) a discount to the price per common share being paid in the Sale of the Company equal to 20% or (b) a conversion price per share based on a pre-sale valuation of $75,000,000 divided by the number of common shares outstanding at that time assuming the hypothetical conversion or exercise of any convertible securities, options, warrants and other rights to acquire common shares of the Company.
NSC [Member]
Debt [Line Items]
Repayments of Debt	$ 3,600