| Cover | Jul. 21, 2021 |
| Cover [Abstract] | |
| Document Type | 8-K |
| Amendment Flag | false |
| Document Period End Date | Jul. 21, 2021 |
| Entity File Number | 001-02658 |
| Entity Registrant Name | STEWART INFORMATION SERVICES CORPORATION |
| Entity Central Index Key | 0000094344 |
| Entity Tax Identification Number | 74-1677330 |
| Entity Incorporation, State or Country Code | DE |
| Entity Address, Address Line One | 1360 Post Oak Blvd |
| Entity Address, Address Line Two | Suite 100 |
| Entity Address, City or Town | Houston |
| Entity Address, State or Province | TX |
| Entity Address, Postal Zip Code | 77056 |
| City Area Code | 713 |
| Local Phone Number | 625-8100 |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Title of 12(b) Security | Common Stock, $1 par value |
| Trading Symbol | STC |
| Security Exchange Name | NYSE |
| Entity Emerging Growth Company | false |
