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	9 Months Ended
	Apr. 23, 2021	Oct. 23, 2020	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2021	Sep. 30, 2021	Sep. 30, 2020
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock offering, aggregate fees paid						$ 85	$ 1,506
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					758,680
Stock offering, price per share				$ 25.00	$ 25.00	$ 25.00
Stock offering, gross proceeds					$ 19,000
Stock offering, aggregate fees paid					1,900
Sale of stock, net proceeds					$ 17,000
Preferred Stock, dividend rate percentage						8.00%
At the Market Offering [Member] \| B. Riley, National Securities Corporation, LifeSci Capital LLC, Maxim Group LLC and Noble Capital Markets, Inc [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock offering, number of shares issued						786,300	16,400,000
Stock offering, price per share			$ 2.74	3.60	$ 3.60	$ 3.60	$ 2.74
Stock offering, gross proceeds						$ 2,800	$ 44,800
Stock offering, aggregate fees paid						$ 100	$ 1,600
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						10,860,983	3,614,344
Stock offering, price per share			2.40	3.42	3.42	$ 3.42	$ 2.40
Stock offering, gross proceeds						$ 37,200	$ 8,700
Sale of stock, net proceeds						$ 36,300	$ 8,400
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						271,515	273,379
Stock offering, price per share			2.92	3.41	3.41	$ 3.41	$ 2.92
At the Market Offering [Member] \| Mustang [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of Shares issuable for At-the-Market offering						52,019
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						17,300,000	7,200,000
Stock offering, price per share			3.56	$ 3.87	3.87	$ 3.87	$ 3.56
Stock offering, gross proceeds						$ 66,900	$ 25,600
Stock offering, aggregate fees paid						$ 1,300	$ 500
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				517,304			117,405
Stock offering, price per share			$ 3.56	$ 3.84	$ 3.84	$ 3.84	$ 3.56
Public Offering [Member] \| Checkpoint [Member] \| Common Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock offering, number of shares issued			7,321,429
Stock offering, price per share			$ 2.80				$ 2.80
Stock offering, gross proceeds			$ 20,500
Stock offering, aggregate fees paid			1,600
Sale of stock, net proceeds			$ 18,900
Shelf Registration Statement [Member] \| Checkpoint [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Amount available for future stock offerings				$ 58,700	$ 58,700	$ 58,700
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				$ 19,300	$ 19,300	$ 19,300