Reinsurance - Current Ratings from Rating Agencies and Unsecured Net Amounts Due from Reinsurers Whose Aggregate Balance Exceeded 3% of Stockholders' Equity (Detail) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Ceded Credit Risk [Line Items]
Reinsurance unsecured amounts due from reinsurers total	$ 114,107	$ 773,345
Florida Hurricane Catastrophe Fund “FHCF”
Ceded Credit Risk [Line Items]
Reinsurance unsecured amounts due from reinsurers total	91,275	134,411
Allianz Risk Transfer (Bermuda) Ltd.
Ceded Credit Risk [Line Items]
Reinsurance unsecured amounts due from reinsurers total	0	285,323
Chubb Tempest Reinsurance Ltd.
Ceded Credit Risk [Line Items]
Reinsurance unsecured amounts due from reinsurers total	0	51,319
Markel Bermuda Ltd.
Ceded Credit Risk [Line Items]
Reinsurance unsecured amounts due from reinsurers total	0	50,981
DaVinci Reinsurance Ltd.
Ceded Credit Risk [Line Items]
Reinsurance unsecured amounts due from reinsurers total	0	48,115
Renaissance Reinsurance Ltd.
Ceded Credit Risk [Line Items]
Reinsurance unsecured amounts due from reinsurers total	0	38,768
D E Shaw Re (Bermuda) Ltd.
Ceded Credit Risk [Line Items]
Reinsurance unsecured amounts due from reinsurers total	0	16,680
Munich Reinsurance America Inc.
Ceded Credit Risk [Line Items]
Reinsurance unsecured amounts due from reinsurers total	0	14,616
Everest Reinsurance Co
Ceded Credit Risk [Line Items]
Reinsurance unsecured amounts due from reinsurers total	0	11,536
Upsilon RFO Re Ltd.
Ceded Credit Risk [Line Items]
Reinsurance unsecured amounts due from reinsurers total	0	11,201
Lumen Re Ltd.
Ceded Credit Risk [Line Items]
Reinsurance unsecured amounts due from reinsurers total	0	8,913
AM Best, A Rating | Standard & Poor's, A Plus Rating | Various Lloyd’s Of London Syndicates
Ceded Credit Risk [Line Items]
Reinsurance unsecured amounts due from reinsurers total	$ 22,832	$ 101,482