Amount of catastrophe bonds.

No definition available.

Name:	aii_AmountOfCatastropheBonds
Namespace Prefix:	aii_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Catastrophe Bond Limit

+ References

No definition available.

+ Details

Name:	aii_CatastropheBondLimit
Namespace Prefix:	aii_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Percentage of third party insurance coverage.

+ References

No definition available.

+ Details

Name:	aii_PercentageOfThirdPartyInsuranceCoverage
Namespace Prefix:	aii_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Reinsurance Agreement Limit

+ References

No definition available.

+ Details

Name:	aii_ReinsuranceAgreementLimit
Namespace Prefix:	aii_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Reinsurance, Ceded Commission Rate

+ References

No definition available.

+ Details

Name:	aii_ReinsuranceCededCommissionRate
Namespace Prefix:	aii_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Reinsurance, Ceded Premiums, Maximum Inuring Reinsurance Coverage, Percentage Of Gross Earned Premiums

+ References

No definition available.

+ Details

Name:	aii_ReinsuranceCededPremiumsMaximumInuringReinsuranceCoveragePercentageOfGrossEarnedPremiums
Namespace Prefix:	aii_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Reinsurance, Ceded Proportional Coverage, Percentage

+ References

No definition available.

+ Details

Name:	aii_ReinsuranceCededProportionalCoveragePercentage
Namespace Prefix:	aii_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Reinsurance contracts recoveries received.

+ References

No definition available.

+ Details

Name:	aii_ReinsuranceContractsRecoveriesReceived
Namespace Prefix:	aii_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Reinsurance Disclosures [Line Items]

+ References

No definition available.

+ Details

Name:	aii_ReinsuranceDisclosuresLineItems
Namespace Prefix:	aii_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Percentage reinsurance participate hurricane season.

+ References

No definition available.

+ Details

Name:	aii_ReinsuranceHurricaneSeasonParticipationPercentage
Namespace Prefix:	aii_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Reinsurance, Loss Coverage, Net Of Reinsurance Coverages, Maximum Percentage Of Net Ceded Premiums Earned

+ References

No definition available.

+ Details

Name:	aii_ReinsuranceLossCoverageNetOfReinsuranceCoveragesMaximumPercentageOfNetCededPremiumsEarned
Namespace Prefix:	aii_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Reinsurance, Net Liability On Catastrophe Losses, Maximum Percentage Of Gross Earned Premium, Net Of Inuring Reinsurance Premium

+ References

No definition available.

+ Details

Name:	aii_ReinsuranceNetLiabilityOnCatastropheLossesMaximumPercentageOfGrossEarnedPremiumNetOfInuringReinsurancePremium
Namespace Prefix:	aii_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Reinsurance premium coverage.

+ References

No definition available.

+ Details

Name:	aii_ReinsurancePremiumCoverage
Namespace Prefix:	aii_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Reinsurance Premiums Earned, Expected

+ References

No definition available.

+ Details

Name:	aii_ReinsurancePremiumsEarnedExpected
Namespace Prefix:	aii_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Reinsurance Return Period

+ References

No definition available.

+ Details

Name:	aii_ReinsuranceReturnPeriod
Namespace Prefix:	aii_
Data Type:	xbrli:pureItemType
Balance Type:	na
Period Type:	duration

- Definition

Reinsurance third party coverage.

+ References

No definition available.

+ Details

Name:	aii_ReinsuranceThirdPartyCoverage
Namespace Prefix:	aii_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Amount per policy of risk undertaken originally by insurer that is not ceded to reinsurer.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 944
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 3
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479838/944-20-50-3

+ Details

Name:	us-gaap_ReinsuranceRetentionAmountRetainedPerPolicy
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Details

Name:	us-gaap_ReinsuranceContractAxis=Quota Share Reinsurance, Net Quota Share Reinsurance
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_SubsequentEventTypeAxis=us-gaap_SubsequentEventMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_ReinsuranceContractAxis=Quota Share Reinsurance, Net Quota Share Reinsurance A
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_RangeAxis=srt_MaximumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_RangeAxis=srt_MinimumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_CededCreditRiskAxis=aii_FirstEventMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_CededCreditRiskAxis=aii_SecondEventMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Reinsurance - Narrative (Details) $ in Thousands		3 Months Ended		6 Months Ended		12 Months Ended
Reinsurance - Narrative (Details) $ in Thousands	Jun. 01, 2026 USD ($)	Jun. 30, 2026 USD ($)	Jun. 30, 2025 USD ($)	Jun. 30, 2026 USD ($)	Jun. 30, 2025 USD ($)	Dec. 31, 2026	Dec. 31, 2025 USD ($)
Reinsurance Disclosures [Line Items]
Third-party reinsurance coverage for single event	$ 2,250,000
Third-party reinsurance coverage across all occurences	$ 2,990,000
Percentage of increase in treaty limit	15.80%
Reinsurance retention policy description period	0.007692
Net retention for events	$ 10,000
Percentage of participated reinsurance for hurricane season	90.00%
Reinsurance agreement	$ 572,700
Catastrophe bond limit	825,000
Catastrophe bonds	260,000						$ 565,000
Recoveries received under reinsurance contracts		$ 24,563	$ 30,041	$ 30,183	$ 67,631,000
Reinsurance Contract [Axis]: Quota Share Reinsurance, Net Quota Share Reinsurance \| Subsequent Event
Reinsurance Disclosures [Line Items]
Ceded coverage percentage						25.00%
Ceded loss limit percentage						116.60%
Catastrophe loss limit percentage						2.50%
Injuring reinsurance limit, percentage						31.00%
Reinsurance Contract [Axis]: Quota Share Reinsurance, Net Quota Share Reinsurance A \| Subsequent Event
Reinsurance Disclosures [Line Items]
Ceded commission rate						68.25%
Reinsurance Contract [Axis]: Quota Share Reinsurance, Net Quota Share Reinsurance B \| Subsequent Event
Reinsurance Disclosures [Line Items]
Ceded commission rate						69.00%
Maximum
Reinsurance Disclosures [Line Items]
Reinsurance premiums earned, expected	440,000
Minimum
Reinsurance Disclosures [Line Items]
Reinsurance premiums earned, expected	430,000
First Event
Reinsurance Disclosures [Line Items]
Net retention for events	35,000
Second Event
Reinsurance Disclosures [Line Items]
Net retention for events	$ 20,000