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, 2019	Dec. 31, 2018
Ceded Credit Risk [Line Items]
Reinsurance unsecured amounts due from reinsurers total	$ 218,916	$ 360,254
Florida Hurricane Catastrophe Fund [Member]
Ceded Credit Risk [Line Items]
Reinsurance unsecured amounts due from reinsurers total	199,647	165,022
Allianz Risk Transfer [Member] | AM Best Company A Plus Rating [Member] | Standard & Poor's, AA Rating [Member] | Moody's, Aa3 Rating [Member]
Ceded Credit Risk [Line Items]
Reinsurance unsecured amounts due from reinsurers total	19,269	139,565
Renaissance Reinsurance Ltd [Member]
Ceded Credit Risk [Line Items]
Reinsurance unsecured amounts due from reinsurers total	0
Renaissance Reinsurance Ltd [Member] | AM Best Company A Plus Rating [Member] | Standard & Poor's, A Plus Rating [Member] | Moody's A1 Rating [Member]
Ceded Credit Risk [Line Items]
Reinsurance unsecured amounts due from reinsurers total		39,459
Chubb Tempest Reinsurance Ltd [Member]
Ceded Credit Risk [Line Items]
Reinsurance unsecured amounts due from reinsurers total	$ 0	$ 16,208