| Document and Entity Information | Jul. 07, 2020 |
| Document And Entity Information [Line Items] | |
| Amendment Flag | false |
| Entity Central Index Key | 0001091748 |
| Current Fiscal Year End Date | --12-31 |
| Document Type | 8-K |
| Document Period End Date | Jul. 7, 2020 |
| Entity Registrant Name | ARGO GROUP INTERNATIONAL HOLDINGS, LTD. |
| Entity Incorporation State Country Code | D0 |
| Entity File Number | 001-15259 |
| Entity Tax Identification Number | 98-0214719 |
| Entity Address, Address Line One | 90 Pitts Bay Road |
| Entity Address, City or Town | Pembroke |
| Entity Address, Postal Zip Code | HM08 |
| Entity Address, Country | BM |
| City Area Code | (441) |
| Local Phone Number | 296-5858 |
| 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 And Entity Information [Line Items] | |
| Security 12b Title | Common Stock, par value of $1.00 per share |
| Trading Symbol | ARGO |
| Security Exchange Name | NYSE |
| Senior Notes [Member] | |
| Document And Entity Information [Line Items] | |
| Security 12b Title | Guarantee of Argo Group U.S., Inc. 6.500% Senior Notes due 2042 |
| Trading Symbol | ARGD |
| Security Exchange Name | NYSE |
