Loss and Loss Adjustment Expenses - Summary Exposures to Various Asbestos Related Claims (Detail) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Asbestos Claims [Line Items]
Balance, beginning of period	$ 798,409	$ 771,845	$ 742,776
Incurred losses and LAE during the current year	176,342	204,891	209,324
Loss and LAE payments	(58,883)	(62,061)	(56,951)
Balance, end of period	772,887	798,409	771,845
Asbestos Issue [Member]
Asbestos Claims [Line Items]
Balance, beginning of period	1,555	1,748	1,487
Incurred losses and LAE during the current year	(183)	108	556
Loss and LAE payments	(49)	(301)	(295)
Balance, end of period	$ 1,323	$ 1,555	$ 1,748

Asbestos Claims [Line Items]

No definition available.

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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://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 40
-Section 50
-Paragraph 3
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=116884095&loc=d3e14764-158437

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 40
-Section 50
-Paragraph 3
-Subparagraph (cc)
-URI http://asc.fasb.org/extlink&oid=116884095&loc=d3e14764-158437

+ Details

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- Definition

Amount, after effects of reinsurance, of payments to settle claims incurred in the current period and related claims settlement costs.

+ References

+ Details

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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

+ Details

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- Details

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