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, 2019	Dec. 31, 2018	Dec. 31, 2017
Liability For Unpaid Claims And Claims Adjustment Expense Net
Unpaid claims balance, beginning	$ 1,481,294
Less reinsurance recoverables	(427,475)
Paid claims related to
Net balance	995,986
Plus reinsurance recoverables	(411,830)	$ (427,475)
Unpaid claims balance, ending	1,489,979	1,481,294
Property and Casualty Accident and Health
Liability For Unpaid Claims And Claims Adjustment Expense Net
Unpaid claims balance, beginning	1,305,225	1,218,652	$ 1,156,681
Less reinsurance recoverables	254,466	241,301	219,832
Net beginning balance	1,050,759	977,351	936,849
Incurred related to
Current	1,207,796	1,193,216	1,107,381
Prior years	(57,979)	(19,852)	(75,632)
Total incurred claims	1,149,817	1,173,364	1,031,749
Paid claims related to
Current	688,544	688,493	653,136
Prior years	435,642	411,463	338,111
Total paid claims	1,124,186	1,099,956	991,247
Net balance	1,076,390	1,050,759	977,351
Plus reinsurance recoverables	246,447	254,466	241,301
Unpaid claims balance, ending	$ 1,322,837	$ 1,305,225	$ 1,218,652