| Document And Entity Information | Aug. 12, 2021 |
| Document Information [Line Items] | |
| Entity, Registrant Name | Safeguard Scientifics, Inc. |
| Document, Type | 8-K |
| Document, Period End Date | Aug. 12, 2021 |
| Entity, Incorporation, State or Country Code | PA |
| Entity, File Number | 1-5620 |
| Entity, Tax Identification Number | 23-1609753 |
| Entity, Address, Address Line One | 150 N. Radnor Chester Rd., STE F-200 |
| Entity, Address, City or Town | Radnor |
| Entity, Address, State or Province | PA |
| Entity, Address, Postal Zip Code | 19087 |
| City Area Code | 610 |
| Local Phone Number | 293-0600 |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Title of 12(b) Security | Common Stock |
| Trading Symbol | SFE |
| Security Exchange Name | NYSE |
| Entity, Emerging Growth Company | false |
| Amendment Flag | false |
| Entity, Central Index Key | 0000086115 |
