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Loss and Loss Adjustment Expenses - Summary Exposures to Various Asbestos Related Claims (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Asbestos Claims [Line Items]
Balance, beginning of period	$ 673,994	$ 696,037	$ 745,278
Incurred losses and LAE during the current year	157,267	148,263	152,316
Balance, end of period	651,309	673,994	696,037
Asbestos Issue [Member]
Asbestos Claims [Line Items]
Balance, beginning of period	310	248	260
Incurred losses and LAE during the current year	14	15	(2)
Loss and LAE payments	(11)	47	(10)
Balance, end of period	$ 313	$ 310	$ 248

X

- Definition

Asbestos Claims [Line Items]

+ References

No definition available.

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- Definition

Loss and loss adjustment expenses payments or recoveries.

+ References

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- Definition

The amount needed to reflect the estimated ultimate cost of settling claims relating to insured events that have occurred on or before the balance sheet date, whether or not reported to the insurer at that date.

+ References

Reference 1: http://www.xbrl.org/2003/role/exampleRef
-Topic 944
-SubTopic 40
-Name Accounting Standards Codification
-Section 55
-Paragraph 7
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480046/944-40-55-7

Reference 2: http://www.xbrl.org/2003/role/exampleRef
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Reference 3: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 944
-SubTopic 40
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-Section 50
-Paragraph 3
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-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480081/944-40-50-3

Reference 4: http://www.xbrl.org/2009/role/commonPracticeRef
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-Name Accounting Standards Codification
-Section S99
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-Subparagraph (SX 210.7-03(a)(13)(a)(1))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147478777/944-210-S99-1

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- Definition

Amount, after effects of reinsurance, of expense (reversal of expense) for claims incurred and costs incurred in the claim settlement process.

+ References

Reference 1: http://www.xbrl.org/2003/role/exampleRef
-Topic 944
-SubTopic 40
-Name Accounting Standards Codification
-Section 55
-Paragraph 7
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480046/944-40-55-7

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-URI https://asc.fasb.org/1943274/2147480081/944-40-50-3

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