Liability for Unpaid Claims and Claim Adjustment Expenses - Liability for Unpaid Claims and Claim Adjustment Expenses (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Liability For Unpaid Claims And Claims Adjustment Expense Net
Unpaid claims balance, beginning	$ 1,390,561
Less reinsurance recoverables	(418,589)
Paid claims related to
Net balance	963,752
Plus reinsurance recoverables	(427,475)	$ (418,589)
Unpaid claims balance, ending	1,481,294	1,390,561
Property and Casualty Accident and Health
Liability For Unpaid Claims And Claims Adjustment Expense Net
Unpaid claims balance, beginning	1,199,233	1,140,723	$ 1,104,302
Less reinsurance recoverables	237,439	216,903	217,337
Net beginning balance	961,794	923,820	886,965
Incurred related to
Current	1,193,216	1,097,730	1,055,796
Prior years	(19,852)	(77,296)	(36,788)
Total incurred claims	1,173,364	1,020,434	1,019,008
Paid claims related to
Current	688,493	661,662	654,175
Prior years	411,463	320,798	327,978
Total paid claims	1,099,956	982,460	982,153
Net balance	1,035,373	961,794	923,820
Plus reinsurance recoverables	254,466	237,439	216,903
Unpaid claims balance, ending	$ 1,289,839	$ 1,199,233	$ 1,140,723