| Cover | May 16, 2021 |
| Document Information [Line Items] | |
| Document Type | 8-K |
| Amendment Flag | false |
| Document Period End Date | May 16, 2021 |
| Entity File Number | 001-35366 |
| Entity Registrant Name | Fortress Biotech, Inc. |
| Entity Central Index Key | 0001429260 |
| Entity Tax Identification Number | 20-5157386 |
| Entity Incorporation, State or Country Code | DE |
| Entity Address, Address Line One | 2 Gansevoort Street |
| Entity Address, Address Line Two | 9th Floor |
| Entity Address, City or Town | New York |
| Entity Address, State or Province | NY |
| Entity Address, Postal Zip Code | 10014 |
| City Area Code | 781 |
| Local Phone Number | 652-4500 |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Entity Emerging Growth Company | false |
| Common Stock [Member] | |
| Document Information [Line Items] | |
| Title of 12(b) Security | Common Stock |
| Trading Symbol | FBIO |
| Security Exchange Name | NASDAQ |
| 9.375% Series A Cumulative Redeemable Perpetual Preferred Stock [Member] | |
| Document Information [Line Items] | |
| Title of 12(b) Security | 9.375% Series A Cumulative Redeemable Perpetual Preferred Stock |
| Trading Symbol | FBIOP |
| Security Exchange Name | NASDAQ |
