Valuation and Qualifying Accounts (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Allowance for uncollectable reinsurance
Valuation and Qualifying Accounts Disclosure [Line Items]
Beginning Balance	$ 6,921	$ 11,332	$ 11,332
Charged (Credited) to Costs and Expenses	5,157	(4,411)
Charged to Other Accounts	0	0	0
Deductions (Describe)	0	0	0
Ending Balance	12,078	6,921	11,332
Valuation allowance in deferred taxes
Valuation and Qualifying Accounts Disclosure [Line Items]
Beginning Balance	721	776	554
Charged (Credited) to Costs and Expenses	(22)	(55)	222
Charged to Other Accounts	0	0	0
Deductions (Describe)	0	0	0
Ending Balance	$ 699	$ 721	$ 776