Transactions with Related Parties - Additional Information (Detail) - Kinetica [Member] $ in Millions	Dec. 31, 2016 USD ($)
Schedule Of Other Related Party Transactions [Line Items]
Surety bonds issued	$ 13
Percentage of investment ownership	10.00%

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

No definition available.

Name:	agii_OwnershipPercentageByDirectorRelatedPartyTransaction
Namespace Prefix:	agii_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant