Reinsurance - 2023-2024 Reinsurance Tower - Catastrophe Excess of Loss Reinsurance - Segmented into Layers of Coverage - SE 1st Event - (Detail) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2023	Jun. 30, 2023
Reinsurance Premiums For Insurance Companies By Product Segment [Line Items]
Excess retention percentage		67.50%
Heritage [Member] \| Layer 4 FL/SE 100% of $60M xs $470M 1@100% [Member] \| First Catastrophe
Reinsurance Premiums For Insurance Companies By Product Segment [Line Items]
Reinsured risk percentage	100.00%
Retention amount reinsured	$ 60.0
Excess retention amount reinsured	$ 470.0
Excess retention percentage	100.00%
Heritage [Member] \| Layer 4 FL/SE 100% of $60M xs $470M 1@100% [Member] \| First Catastrophe \| Maximum [Member]
Reinsurance Premiums For Insurance Companies By Product Segment [Line Items]
Retention under program to provide reinsurance coverage	$ 1,120.3
Heritage [Member] \| Layer 3 Ex- HI 100% of $80M xs $390M 1@100% [Member] \| First Catastrophe
Reinsurance Premiums For Insurance Companies By Product Segment [Line Items]
Reinsured risk percentage	100.00%
Retention amount reinsured	$ 80.0
Excess retention amount reinsured	$ 390.0
Excess retention percentage	100.00%
Heritage [Member] \| Layer 3 Ex- HI 100% of $80M xs $390M 1@100% [Member] \| First Catastrophe \| Minimum [Member]
Reinsurance Premiums For Insurance Companies By Product Segment [Line Items]
Retention under program to provide reinsurance coverage	$ 1,060.3
Heritage [Member] \| FHCF Layer 90% of $564.3M xs $274.5M($507.9M) [Member] \| First Catastrophe
Reinsurance Premiums For Insurance Companies By Product Segment [Line Items]
Retention under program to provide reinsurance coverage	$ 838.8
Reinsured risk percentage	90.00%
Retention amount reinsured	$ 564.3
Excess retention amount reinsured	274.5
Additional excess retention amount reinsured	507.9
Heritage [Member] \| FHCF Layer 90% of $564.3M xs $274.5M($507.9M) [Member] \| First Catastrophe \| Maximum [Member]
Reinsurance Premiums For Insurance Companies By Product Segment [Line Items]
Retention under program to provide reinsurance coverage	980.3
Heritage [Member] \| FHCF Layer 90% of $564.3M xs $274.5M($507.9M) [Member] \| First Catastrophe \| Minimum [Member]
Reinsurance Premiums For Insurance Companies By Product Segment [Line Items]
Retention under program to provide reinsurance coverage	$ 274.5
Heritage [Member] \| Layer 2 100% of $250M xs $140M 1@100% w/RPP [Member] \| First Catastrophe
Reinsurance Premiums For Insurance Companies By Product Segment [Line Items]
Reinsured risk percentage	100.00%
Retention amount reinsured	$ 250.0
Excess retention amount reinsured	$ 140.0
Excess retention percentage	100.00%
Heritage [Member] \| Layer 2 100% of $250M xs $140M 1@100% w/RPP [Member] \| First Catastrophe \| Minimum [Member]
Reinsurance Premiums For Insurance Companies By Product Segment [Line Items]
Retention under program to provide reinsurance coverage	$ 192.1
Heritage [Member] \| RAP Layer 90% of $91.6M xs $192.1M ($82.4M) [Member] \| First Catastrophe
Reinsurance Premiums For Insurance Companies By Product Segment [Line Items]
Reinsured risk percentage	90.00%
Retention amount reinsured	$ 91.6
Excess retention amount reinsured	192.1
Additional excess retention amount reinsured	82.4
Heritage [Member] \| RAP Layer 90% of $91.6M xs $192.1M ($82.4M) [Member] \| First Catastrophe \| Minimum [Member]
Reinsurance Premiums For Insurance Companies By Product Segment [Line Items]
Retention under program to provide reinsurance coverage	283.7
Heritage [Member] \| Layer 1 100% of $100M xs $40M 1@100% w/ RPP [Member] \| First Catastrophe
Reinsurance Premiums For Insurance Companies By Product Segment [Line Items]
Retention under program to provide reinsurance coverage	$ 140.0
Reinsured risk percentage	100.00%
Retention amount reinsured	$ 100.0
Excess retention amount reinsured	$ 40.0
Excess retention percentage	100.00%
Heritage [Member] \| Retention [Member] \| First Catastrophe
Reinsurance Premiums For Insurance Companies By Product Segment [Line Items]
Retention under program to provide reinsurance coverage	$ 40.0
Reinsurance retention policy, description	Retention

Reinsurance retention policy additional excess retention amount reinsured.

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Reinsurance retention policy, retention, amount reinsured.

+ References

No definition available.

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- Definition

Retention policy description.

+ References

No definition available.

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name Regulation S-X (SX)
-Number 210
-Section 12
-Subsection 17
-Publisher SEC

Reference 2: 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 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 B))
-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 C))
-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 D))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480149/944-235-S99-2

Reference 6: 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 7: 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 F))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480149/944-235-S99-2

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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

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

+ References

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- Definition

Percentage of risk ceded to reinsurer in excess of risk undertaken originally by insurer that is not ceded to reinsurer.

+ References

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- Definition

Percentage of risk undertaken originally by insurer ceded to reinsurer.

+ References

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