Investments - Schedule of Loans by Maturity (Details) $ in Millions	Mar. 31, 2025 USD ($) loan	Dec. 31, 2024 USD ($) loan
Cost
Cost	$ 836.1	$ 787.4
Mortgage Loans
Cost
One year or less	95.4	34.9
Greater than one year and less than three	48.3	103.5
Greater than three years and less than five years	17.9	17.7
Greater than seven years and less than ten years	56.7	54.0
Cost	$ 218.3	$ 210.1
Loan Count
One year or less \| loan	8	3
Greater than one year and less than three \| loan	5	7
Greater than three years and less than five years \| loan	2	2
Greater than seven years and less than ten years \| loan	8	5
Loan Count \| loan	23	17

Financing Receivable, before Allowance for Credit Loss, Maturity, Greater than One Year and Less than Three

No definition available.

Name:	argo_FinancingReceivableBeforeAllowanceForCreditLossMaturityGreaterThanOneYearAndLessThanThree
Namespace Prefix:	argo_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Financing Receivable, before Allowance for Credit Loss, Maturity, Greater than One Year and Less than Three, Number of Loans

+ References

No definition available.

+ Details

Name:	argo_FinancingReceivableBeforeAllowanceForCreditLossMaturityGreaterThanOneYearAndLessThanThreeNumberOfLoans
Namespace Prefix:	argo_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

Financing Receivable, before Allowance for Credit Loss, Maturity, Greater than Seven Years and Less than Ten Years

+ References

No definition available.

+ Details

Name:	argo_FinancingReceivableBeforeAllowanceForCreditLossMaturityGreaterThanSevenYearsAndLessThanTenYears
Namespace Prefix:	argo_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Financing Receivable, before Allowance for Credit Loss, Maturity, Greater than Seven Years and Less than Ten Years, Number of Loans

+ References

No definition available.

+ Details

Name:	argo_FinancingReceivableBeforeAllowanceForCreditLossMaturityGreaterThanSevenYearsAndLessThanTenYearsNumberOfLoans
Namespace Prefix:	argo_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

Financing Receivable, before Allowance for Credit Loss, Maturity, Greater than Three Years and Less than Five Years

+ References

No definition available.

+ Details

Name:	argo_FinancingReceivableBeforeAllowanceForCreditLossMaturityGreaterThanThreeYearsAndLessThanFiveYears
Namespace Prefix:	argo_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Financing Receivable, before Allowance for Credit Loss, Maturity, Greater than Three Years and Less than Five Years, Number of Loans

+ References

No definition available.

+ Details

Name:	argo_FinancingReceivableBeforeAllowanceForCreditLossMaturityGreaterThanThreeYearsAndLessThanFiveYearsNumberOfLoans
Namespace Prefix:	argo_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

Financing Receivable, before Allowance for Credit Loss, Maturity, One Year or Less

+ References

No definition available.

+ Details

Name:	argo_FinancingReceivableBeforeAllowanceForCreditLossMaturityOneYearOrLess
Namespace Prefix:	argo_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Financing Receivable, before Allowance for Credit Loss, Maturity, One Year or Less, Number of Loans

+ References

No definition available.

+ Details

Name:	argo_FinancingReceivableBeforeAllowanceForCreditLossMaturityOneYearOrLessNumberOfLoans
Namespace Prefix:	argo_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

Financing Receivable, before Allowance for Credit Loss, Number of Loans

+ References

No definition available.

+ Details

Name:	argo_FinancingReceivableBeforeAllowanceForCreditLossNumberOfLoans
Namespace Prefix:	argo_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

Financing Receivable, Loan Count

+ References

No definition available.

+ Details

Name:	argo_FinancingReceivableLoanCountAbstract
Namespace Prefix:	argo_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Amortized cost excluding accrued interest, before allowance for credit loss, of financing receivable. Excludes net investment in lease.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 326
-SubTopic 20
-Name Accounting Standards Codification
-Section 45
-Paragraph 1
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479344/326-20-45-1

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 326
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 3B
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479319/326-20-50-3B

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 326
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 5
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479319/326-20-50-5

+ Details

Name:	us-gaap_FinancingReceivableExcludingAccruedInterestBeforeAllowanceForCreditLoss
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- References

No definition available.

+ Details

Name:	us-gaap_FinancingReceivableUnamortizedLoanFeeCostAndPurchasePremiumDiscountAbstract
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=argo_MortgageLoansMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: