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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, 2022
Dec. 31, 2021
Dec. 31, 2020
Premiums Written and Earned [Abstract]      
Written, Direct $ 24.4 $ 30.9 $ 37.7
Written, Assumed 0.4 0.2 0.1
Written, Ceded (24.8) (31.1) (37.8)
Earned, Direct 28.7 35.9 40.7
Earned, Assumed 0.2 0.2 0.9
Earned, Ceded $ (28.9) $ (36.1) $ (41.6)