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Third-Party Reinsurance - Remaining Gross and Net Reinsurance Recoverables (Details) $ in Millions	Jun. 30, 2023 USD ($)
All Entities Except TCP Providers
Reinsurance [Line Items]
Reinsurance recoverables	$ 386.0
Reinsurance Recoverables, Collateral	100.5
Net Reinsurance Recoverables	$ 285.5
Percent of reinsurance recoverables from insurers that are collateralized	100.00%
P&C Insurance and Reinsurance (Ark/WM Outrigger)
Reinsurance [Line Items]
Reinsurance recoverables on unpaid losses	$ 0.6
A+ or better | All Entities Except TCP Providers
Reinsurance [Line Items]
Reinsurance recoverables	197.5
Reinsurance Recoverables, Collateral	0.0
Net Reinsurance Recoverables	$ 197.5
Percent of reinsurance recoverables from insurers that are collateralized	69.20%
A- to A | All Entities Except TCP Providers
Reinsurance [Line Items]
Reinsurance recoverables	$ 78.3
Reinsurance Recoverables, Collateral	0.0
Net Reinsurance Recoverables	$ 78.3
Percent of reinsurance recoverables from insurers that are collateralized	27.40%
B++ or lower and not rated | All Entities Except TCP Providers
Reinsurance [Line Items]
Reinsurance recoverables	$ 110.2
Reinsurance Recoverables, Collateral	100.5
Net Reinsurance Recoverables	$ 9.7
Percent of reinsurance recoverables from insurers that are collateralized	3.40%

X

- Definition

Amount, after valuation allowance, recoverable under reinsurance contracts including premium paid under reinsurance contracts. Examples include, but are not limited to, settled and unsettled claims, incurred but not reported losses, loss adjustment expense, premium paid, policy benefits and policy reserves.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 944
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 5
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147479838/944-20-50-5

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 944
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-Name Accounting Standards Codification
-Section 45
-Paragraph 5
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147479616/944-310-45-5

Reference 3: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 944
-SubTopic 210
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03(a)(6))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147479440/944-210-S99-1

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- Definition

Amount before valuation allowance recoverable under reinsurance contracts. Examples include, but are not limited to, settled and unsettled claims, incurred but not reported losses, loss adjustment expense, premium paid, policy benefits and policy reserves.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 944
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 5
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147479838/944-20-50-5

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
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-Section S99
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-Publisher FASB
-URI https://asc.fasb.org//1943274/2147479440/944-210-S99-1

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 944
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-Section 45
-Paragraph 5
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147479616/944-310-45-5

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Topic 326
-SubTopic 20
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-Section 50
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Reference 5: http://www.xbrl.org/2003/role/disclosureRef
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-Topic 310
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Amount before valuation allowance of reinsurance recoverables for losses reported to the ceding insurer but not yet paid, and for amounts expected based upon statistical projections and other measures of incurred losses and loss settlement expenses which have not yet been reported to the ceding insurer.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 944
-SubTopic 310
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147479584/944-310-50-2

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
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-Publisher FASB
-URI https://asc.fasb.org//1943274/2147479838/944-20-50-5

Reference 3: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 944
-SubTopic 310
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-Section 45
-Paragraph 6
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147479616/944-310-45-6

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- Definition

Percentage of Reinsurance Recoverables from Insurers, Collateralized

+ References

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