Cover - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Mar. 09, 2021	Jun. 30, 2020
Document Information [Line Items]
Document Type	10-K
Document Annual Report	true
Document Period End Date	Dec. 31, 2020
Document Transition Report	false
Entity File Number	1-15259
Entity Registrant Name	ARGO GROUP INTERNATIONAL HOLDINGS, LTD.
Entity Incorporation, State or Country Code	D0
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
Entity Well-known Seasoned Issuer	No
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
ICFR Auditor Attestation Flag	true
Entity Shell Company	false
Entity Public Float			$ 1,151.6
Entity Common Stock, Shares Outstanding		34,706,786
Documents Incorporated by Reference	Part III of this report incorporates by reference specific portions of the Registrant's Proxy Statement relating to the 2021 Annual General Meeting of Shareholders.
Entity Central Index Key	0001091748
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	FY
Amendment Flag	false
Common Shares
Document Information [Line Items]
Title of 12(b) Security	Common Stock, par value of $1.00 per share
Trading Symbol	ARGO
Security Exchange Name	NYSE
Guarantee of Argo Group U.S., Inc. 6.500% Senior Notes due 2042
Document Information [Line Items]
Title of 12(b) Security	Argo Group U.S., Inc. 6.500% Senior Notes due 2042 and the Guarantee with respects thereto
Trading Symbol	ARGD
Security Exchange Name	NYSE
Depositary Shares
Document Information [Line Items]
Title of 12(b) Security	Depositary Shares, each representing a 1/1000th Interest in a shareof Series A 7.00% Non-Cumulative Preference Shares, par value $1.00 per share
Trading Symbol	ARGOPrA
Security Exchange Name	NYSE