Transactions with Related Parties Transactions with Related Parties (Detail) - Kinetica - Affiliated Entity - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2013
Schedule Of Other Related Party Transactions [Line Items]
Surety bonds issued		$ 13
Percentage of investment ownership		10.00%
Surety bonds outstanding	$ 12

Percentage ownership by Board of Directors member in entity with which the company has a related party transaction.

No definition available.

Name:	argo_OwnershipPercentageByDirectorRelatedPartyTransaction
Namespace Prefix:	argo_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant