Reinsurance - Current Ratings from Rating Agencies and Unsecured Net Amounts Due from Insurance Entities' Reinsurers Whose Aggregate Balance Exceeded 3% of Stockholders' Equity (Detail) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Ceded Credit Risk [Line Items]
Reinsurance unsecured amounts due from reinsurers	$ 97,694	$ 218,916
Florida Hurricane Catastrophe Fund [Member]
Ceded Credit Risk [Line Items]
Reinsurance unsecured amounts due from reinsurers	97,694	199,647
Allianz Risk Transfer [Member]
Ceded Credit Risk [Line Items]
Reinsurance unsecured amounts due from reinsurers	$ 0
Allianz Risk Transfer [Member] | AM Best Company A+ [Member] | Standard and Poor's AA [Member] | Moody's Investors Service Aa3 [Member]
Ceded Credit Risk [Line Items]
Reinsurance unsecured amounts due from reinsurers		$ 19,269