| Document and Entity Information | Oct. 21, 2020 |
| Document And Entity Information [Line Items] | |
| Entity Address, Country | BM |
| Amendment Flag | false |
| Entity Central Index Key | 0001091748 |
| Document Type | 8-K |
| Document Period End Date | Oct. 21, 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 | 110 Pitts Bay Road |
| Entity Address, Address Line Two | 110 Pitts Bay Road |
| Entity Address, City or Town | Pembroke |
| Entity Address, Postal Zip Code | HM 08 |
| 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 |
| Guaranteeof Argo Group U . S . Inc .6.500 Senior Notesdue 2042 [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 |
| Depositary Shares Each Representing A 11000th Interest In A 7.00 Resettable Fixed Rate Preference Share Series A Par Value 1.00 Per Share [Member] | |
| Document And Entity Information [Line Items] | |
| Security 12b Title | Depositary Shares, Each Representing a 1/1,000th Interest in a 7.00% Resettable Fixed Rate Preference Share, Series A, Par Value $1.00 Per Share |
| Trading Symbol | ARGOPrA |
| Security Exchange Name | NYSE |
