Liability for Unpaid Claims and Claim Adjustment Expenses - Liability for Unpaid Claims and Claim Adjustment Expenses (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Liability For Unpaid Claims And Claims Adjustment Expense Net
Unpaid claims balance, beginning	$ 1,489,979
Paid claims related to
Unpaid claims balance, ending	1,470,080
Property and Casualty Accident and Health
Liability For Unpaid Claims And Claims Adjustment Expense Net
Unpaid claims balance, beginning	1,322,837	$ 1,305,225
Less: Reinsurance recoverables	246,447	254,466
Net beginning balance	1,076,390	1,050,759
Incurred related to
Current	260,025	278,864
Prior years	4,172	(17,296)
Total incurred claims	264,197	261,568
Paid claims related to
Current	95,635	93,273
Prior years	174,986	168,879
Total paid claims	270,621	262,152
Net balance	1,069,966	1,050,175
Plus: Reinsurance recoverables	244,230	244,098
Unpaid claims balance, ending	$ 1,314,196	$ 1,294,273