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

Stockholders' Equity (Capital Raises) (Narrative) (Details)

Stockholders' Equity (Capital Raises) (Narrative) (Details) - USD ($) $ / shares in Units, $ in Thousands			1 Months Ended		3 Months Ended	6 Months Ended
	Apr. 23, 2021	Oct. 23, 2020	Jul. 31, 2021	Mar. 31, 2021	Jun. 30, 2021	Jun. 30, 2021	Jun. 30, 2020	Dec. 31, 2020
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock offering, aggregate fees paid						$ 0	$ 793
Preferred Stock, liquidation preference per share					$ 25.00	$ 25.00		$ 25.00
Journey [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock offering, gross proceeds			$ 4,600
Stock offering, aggregate fees paid			500
Sale of stock, net proceeds			$ 4,200
Journey [Member] \| 8% Cumulative Convertible Class A Preferred Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock offering, number of shares issued						573,280
Stock offering, price per share					25.00	$ 25.00
Stock offering, gross proceeds						$ 14,300
Stock offering, aggregate fees paid						1,400
Sale of stock, net proceeds						$ 12,600
Preferred Stock, dividend rate percentage				8.00%		8.00%
At the Market Offering [Member] \| MLV & Co. and FBR Capital Markets & Co [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock offering, number of shares issued						0	9,300,000
Stock offering, price per share							$ 2.47
Stock offering, gross proceeds							$ 23,000
Stock offering, aggregate fees paid							$ 700
At the Market Offering [Member] \| Checkpoint [Member] \| Common Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock offering, number of shares issued						10,400,000	1,303,282
Stock offering, price per share					3.42	$ 3.42	$ 2.05
Stock offering, gross proceeds						$ 35,600	$ 2,700
Sale of stock, net proceeds						$ 34,700	$ 2,600
At the Market Offering [Member] \| Checkpoint [Member] \| Common Stock [Member] \| Founders Agreement [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock offering, number of shares issued						259,990	32,571
Stock offering, price per share					3.41	$ 3.41	$ 2.01
At the Market Offering [Member] \| Mustang [Member] \| Common Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock offering, number of shares issued						16,200,000	2,100,000
Stock offering, price per share					$ 3.94	$ 3.94	$ 3.76
Stock offering, gross proceeds						$ 63,800	$ 8,000
Stock offering, aggregate fees paid						$ 1,200	$ 100
At the Market Offering [Member] \| Mustang [Member] \| Common Stock [Member] \| Founders Agreement [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock offering, number of shares issued					452,965		53,390
Stock offering, price per share					$ 3.50	$ 3.50	$ 3.76
Shelf Registration Statement [Member] \| Checkpoint [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Amount available for future stock offerings					$ 60,300	$ 60,300
Shelf Registration Statement [Member] \| Mustang [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock offering, number of shares issued						0
Stock offering, aggregate offering permitted by the agreement	$ 200,000	$ 100,000
Amount available for future stock offerings					$ 22,300	$ 22,300