Insurance Operations - Summary of Reconciliations of Direct to Net premiums on Written and Earned Basis Related to Wholly Owned Underwriting Enterprise Subsidiary (Detail) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Premiums Written and Earned [Abstract]
Written, Direct	$ 19.8	$ 24.4	$ 30.9
Written, Assumed		0.4	0.2
Written, Ceded	(19.8)	(24.8)	(31.1)
Earned, Direct	24.8	28.7	35.9
Earned, Assumed	0.4	0.2	0.2
Earned, Ceded	$ (25.2)	$ (28.9)	$ (36.1)

Amount of earned premiums assumed from other entities.

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Amount of written premiums assumed from other entities.

+ References

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-Topic 944
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Amount of earned premiums ceded to other entities.

+ References

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Amount of written premiums ceded to other entities.

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Amount, before premiums ceded to other entities and premiums assumed by the entity, of premiums earned.

+ References

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Amount, before premiums ceded to other entities and premiums assumed by the entity, of premiums written.

+ References

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