Reserve for Known and Incurred but Not Reported Claims (Activity in Reserve for Known and Incurred but Not Reported Claims) (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]
Balance at beginning of period	$ 1,042,679	$ 1,028,933
Provision related to current year	88,603	90,970
Provision related to prior years	9,109	9,610
Total Provision	97,712	100,580
Payments, net of recoveries, related to: Current year	30,446	32,285
Payments, net of recoveries, related to: Prior years	69,546	72,329
Total Payments, net of recoveries	99,992	104,614
Other	(6,765)	(3,553)
Balance at end of period	$ 1,033,634	$ 1,021,346