Reinsurance - 2023 - 2024 Reinsurance Program - Catastrophe Excess of Loss Reinsurance - Additional information - (Detail) $ in Millions	9 Months Ended
Sep. 30, 2023 USD ($)
FHCF [Member]
SEC Schedule, 12-17, Insurance Companies, Reinsurance [Line Items]
Reinsured risk percentage	90.00%
2023 - 2024 Reinsurance Program [Member]
SEC Schedule, 12-17, Insurance Companies, Reinsurance [Line Items]
Reinsurance purchase limit	$ 2,900.0
First Catastrophe [Member] \| 2023 - 2024 Reinsurance Program [Member] \| NBIC [Member] \| Maximum [Member]
SEC Schedule, 12-17, Insurance Companies, Reinsurance [Line Items]
Retention under program to provide reinsurance coverage	1,300.0
First event retention for insurance company subsidiary	30.0
First Catastrophe [Member] \| 2023 - 2024 Reinsurance Program [Member] \| Heritage P&C [Member] \| Maximum [Member]
SEC Schedule, 12-17, Insurance Companies, Reinsurance [Line Items]
Retention under program to provide reinsurance coverage	1,100.0
First event retention for insurance company subsidiary	40.0
First Catastrophe [Member] \| 2023 - 2024 Reinsurance Program [Member] \| Zephyr [Member] \| Maximum [Member]
SEC Schedule, 12-17, Insurance Companies, Reinsurance [Line Items]
Retention under program to provide reinsurance coverage	870.0
First event retention for insurance company subsidiary	40.0
First Catastrophe [Member] \| 2023 - 2024 Reinsurance Program [Member] \| Osprey And Zephyr [Member] \| Maximum [Member]
SEC Schedule, 12-17, Insurance Companies, Reinsurance [Line Items]
First event retention for insurance company subsidiary	30.0
First Catastrophe [Member] \| 2023 - 2024 Reinsurance Program [Member] \| Osprey And NBIC [Member] \| Maximum [Member]
SEC Schedule, 12-17, Insurance Companies, Reinsurance [Line Items]
First event retention for insurance company subsidiary	30.0
Osprey [Member] \| First Catastrophe [Member] \| 2023 - 2024 Reinsurance Program [Member] \| Maximum [Member]
SEC Schedule, 12-17, Insurance Companies, Reinsurance [Line Items]
First event retention for insurance company subsidiary	$ 40.0

Liability for claims and claims for purchase limit.

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- References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 944
-SubTopic 235
-Name Accounting Standards Codification
-Section S99
-Paragraph 2
-Subparagraph (SX 210.12-17(Column A))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480149/944-235-S99-2

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 944
-SubTopic 235
-Name Accounting Standards Codification
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-Paragraph 2
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-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480149/944-235-S99-2

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 944
-SubTopic 235
-Name Accounting Standards Codification
-Section S99
-Paragraph 2
-Subparagraph (SX 210.12-17(Column C))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480149/944-235-S99-2

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Topic 944
-SubTopic 235
-Name Accounting Standards Codification
-Section S99
-Paragraph 2
-Subparagraph (SX 210.12-17(Column D))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480149/944-235-S99-2

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Topic 944
-SubTopic 235
-Name Accounting Standards Codification
-Section S99
-Paragraph 2
-Subparagraph (SX 210.12-17(Column E))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480149/944-235-S99-2

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Topic 944
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-Section S99
-Paragraph 2
-Subparagraph (SX 210.12-17(Column F))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480149/944-235-S99-2

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- Definition

Liability as of the balance sheet date for the estimated ultimate cost of settling claims and claim adjustment expense relating to insured events that have occurred on or before the balance sheet date for those liabilities owed to another party as a result of assuming another insurer's primary obligation.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Topic 944
-SubTopic 40
-Name Accounting Standards Codification
-Section 50
-Paragraph 3
-Subparagraph (cc)
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- 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

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- Definition

Percentage of risk undertaken originally by insurer ceded to reinsurer.

+ References

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