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		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 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			194,000	199,165
Provision related to prior years			12,842	15,034
Total Provision	$ 109,130	$ 113,619	206,842	214,199
Payments, net of recoveries, related to: Current year			85,811	90,752
Payments, net of recoveries, related to: Prior years			114,084	122,786
Total Payments, net of recoveries			199,895	213,538
Other			(7,418)	(6,666)
Balance at end of period	$ 1,042,208	$ 1,022,928	$ 1,042,208	$ 1,022,928