Investments - Schedule of Changes in Assets Measured at Fair Value on a Recurring Basis Using Significant Unobservable Inputs (Level 3) (Detail) - USD ($) $ in Thousands	9 Months Ended
Sep. 30, 2022	Sep. 30, 2021
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation
Beginning Balance	$ 705,193	$ 798,973
Included in realized gains/losses	0	(4,136)
Included in other comprehensive income	(127,688)	(2,801)
Acquisitions	0	25,000
Sales	0	(26,064)
Amortization	3,388	3,396
Other	(45,733)	(77,037)
Transfers into Level 3	0	0
Transfers out of Level 3	0	0
Ending Balance	$ 535,160	$ 717,331
Percentage of total	3.00%	3.00%
Asset- backed Securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation
Beginning Balance	$ 0	$ 12,870
Included in realized gains/losses	0	(82)
Included in other comprehensive income	0	63
Acquisitions	0	0
Sales	0	(12,851)
Amortization	0	0
Other	0	0
Transfers into Level 3	0	0
Transfers out of Level 3	0	0
Ending Balance	$ 0	$ 0
Percentage of total	0.00%	0.00%
Collateralized debt obligations
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation
Beginning Balance	$ 63,505	$ 71,598
Included in realized gains/losses	0	(6,787)
Included in other comprehensive income	(13,163)	12,482
Acquisitions	0	0
Sales	0	(13,213)
Amortization	3,382	3,388
Other	(3,129)	(4,307)
Transfers into Level 3	0	0
Transfers out of Level 3	0	0
Ending Balance	$ 50,595	$ 63,161
Percentage of total	0.00%	0.00%
Corporates
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation
Beginning Balance	$ 641,688	$ 714,505
Included in realized gains/losses	0	2,733
Included in other comprehensive income	(114,525)	(15,346)
Acquisitions	0	25,000
Sales	0	0
Amortization	6	8
Other	(42,604)	(72,730)
Transfers into Level 3	0	0
Transfers out of Level 3	0	0
Ending Balance	$ 484,565	$ 654,170
Percentage of total	3.00%	3.00%

Fair value, measurement with unobservable inputs reconciliation, recurring basis, asset, amortization.

No definition available.

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- Definition

Other adjustments, including capitalized interest and foreign exchange.

+ References

No definition available.

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- Definition

Percent Of Available For Sale Securities At Fair Value By Valuation Level

+ References

No definition available.

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- Definition

A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

+ References

No definition available.

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- Definition

Amount of gain (loss) recognized in income from asset measured at fair value on recurring basis using unobservable input (level 3).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(1)
-URI https://asc.fasb.org/extlink&oid=126976982&loc=d3e19207-110258

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- Definition

Amount of gain (loss) recognized in other comprehensive income (OCI) from asset measured at fair value on recurring basis using unobservable input (level 3).

+ References

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-Publisher FASB
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-Section 50
-Paragraph 2
-Subparagraph (c)(1a)
-URI https://asc.fasb.org/extlink&oid=126976982&loc=d3e19207-110258

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- Definition

Amount of purchases of financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

+ References

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-Publisher FASB
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-SubTopic 10
-Section 50
-Paragraph 2
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-URI https://asc.fasb.org/extlink&oid=126976982&loc=d3e19207-110258

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- Definition

Amount of sale of financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

+ References

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- Definition

Amount of transfer of financial instrument classified as an asset into level 3 of the fair value hierarchy.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(3)
-URI https://asc.fasb.org/extlink&oid=126976982&loc=d3e19207-110258

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- Definition

Amount of transfers of financial instrument classified as an asset out of level 3 of the fair value hierarchy.

+ References

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(3)
-URI https://asc.fasb.org/extlink&oid=126976982&loc=d3e19207-110258

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- Definition

Fair value of financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

+ References

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-SubTopic 10
-Section 50
-Paragraph 2
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