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		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]
Balance at beginning of period			$ 1,025,863	$ 983,880
Provision related to current year			330,342	345,556
Provision related to prior years			3,353	20,917
Total Provision	$ 120,349	$ 137,015	333,695	366,473
Payments, net of recoveries, related to: Current year			165,914	160,693
Payments, net of recoveries, related to: Prior years			185,483	190,656
Total Payments, net of recoveries			351,397	351,349
Other			13,487	19,036
Balance at end of period	$ 1,021,648	$ 1,018,040	$ 1,021,648	$ 1,018,040