Valuation and Qualifying Accounts (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Allowance for Uncollectable Reinsurance
Valuation and Qualifying Accounts Disclosure [Line Items]
Beginning Balance	$ 12,597	$ 12,078	$ 6,921
Charged (Credited) to Costs and Expenses	770	519	5,157
Charged to Other Accounts	0	0	0
Deductions (Describe)	0	0	0
Ending Balance	13,367	12,597	12,078
Valuation Allowance in Deferred Taxes
Valuation and Qualifying Accounts Disclosure [Line Items]
Beginning Balance	1,798	699	721
Charged (Credited) to Costs and Expenses	3,897	1,099	(22)
Charged to Other Accounts	0	0	0
Deductions (Describe)	(1,328)	0	0
Ending Balance	$ 4,367	$ 1,798	$ 699