Segment and Related Information - Additional Information (Detail) $ in Millions	12 Months Ended
Dec. 31, 2023 USD ($) Segment	Dec. 31, 2022 USD ($)	Dec. 31, 2021 USD ($)
Segment Reporting Information [Line Items]
Reportable segments \| Segment	3
Investment income (expense)	$ 292.2	$ 61.0	$ 15.5
Other Segments \| Intersegment
Segment Reporting Information [Line Items]
Investment income (expense)	$ 12.4	$ (1.9)	$ 0.4

Amount after accretion (amortization) of discount (premium), and investment expense, of interest income and dividend income on nonoperating securities.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Topic 220
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03.8)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147483621/220-10-S99-2

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Topic 220
-SubTopic 10
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-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03.7(a),(b))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147483621/220-10-S99-2

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Number of segments reported by the entity. A reportable segment is a component of an entity for which there is an accounting requirement to report separate financial information on that component in the entity's financial statements.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 280
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 18
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482810/280-10-50-18

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