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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, 2021
Dec. 31, 2020
Dec. 31, 2019
Premiums Written And Earned [Abstract]      
Written, Direct $ 30.9 $ 37.7 $ 44.6
Written, Assumed 0.2 0.1 1.0
Written, Ceded (31.1) (37.8) (45.6)
Earned, Direct 35.9 40.7 59.1
Earned, Assumed 0.2 0.9 1.9
Earned, Ceded $ (36.1) $ (41.6) $ (61.0)